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28 \title Developer documentation for Simon Tatham's puzzle collection
30 This is a guide to the internal structure of Simon Tatham's Portable
31 Puzzle Collection (henceforth referred to simply as \q{Puzzles}),
32 for use by anyone attempting to implement a new puzzle or port to a
35 This guide is believed correct as of r6190. Hopefully it will be
36 updated along with the code in future, but if not, I've at least
37 left this version number in here so you can figure out what's
38 changed by tracking commit comments from there onwards.
40 \C{intro} Introduction
42 The Puzzles code base is divided into four parts: a set of
43 interchangeable front ends, a set of interchangeable back ends, a
44 universal \q{middle end} which acts as a buffer between the two, and
45 a bunch of miscellaneous utility functions. In the following
46 sections I give some general discussion of each of these parts.
48 \H{intro-frontend} Front end
50 The front end is the non-portable part of the code: it's the bit
51 that you replace completely when you port to a different platform.
52 So it's responsible for all system calls, all GUI interaction, and
53 anything else platform-specific.
55 The current front ends in the main code base are for Windows, GTK
56 and MacOS X; I also know of a third-party front end for PalmOS.
58 The front end contains \cw{main()} or the local platform's
59 equivalent. Top-level control over the application's execution flow
60 belongs to the front end (it isn't, for example, a set of functions
61 called by a universal \cw{main()} somewhere else).
63 The front end has complete freedom to design the GUI for any given
64 port of Puzzles. There is no centralised mechanism for maintaining
65 the menu layout, for example. This has a cost in consistency (when I
66 \e{do} want the same menu layout on more than one platform, I have
67 to edit two pieces of code in parallel every time I make a change),
68 but the advantage is that local GUI conventions can be conformed to
69 and local constraints adapted to. For example, MacOS X has strict
70 human interface guidelines which specify a different menu layout
71 from the one I've used on Windows and GTK; there's nothing stopping
72 the OS X front end from providing a menu layout consistent with
75 Although the front end is mostly caller rather than the callee in
76 its interactions with other parts of the code, it is required to
77 implement a small API for other modules to call, mostly of drawing
78 functions for games to use when drawing their graphics. The drawing
79 API is documented in \k{drawing}; the other miscellaneous front end
80 API functions are documented in \k{frontend-api}.
82 \H{intro-backend} Back end
84 A \q{back end}, in this collection, is synonymous with a \q{puzzle}.
85 Each back end implements a different game.
87 At the top level, a back end is simply a data structure, containing
88 a few constants (flag words, preferred pixel size) and a large
89 number of function pointers. Back ends are almost invariably callee
90 rather than caller, which means there's a limitation on what a back
91 end can do on its own initiative.
93 The persistent state in a back end is divided into a number of data
94 structures, which are used for different purposes and therefore
95 likely to be switched around, changed without notice, and otherwise
96 updated by the rest of the code. It is important when designing a
97 back end to put the right pieces of data into the right structures,
98 or standard midend-provided features (such as Undo) may fail to
101 The functions and variables provided in the back end data structure
102 are documented in \k{backend}.
104 \H{intro-midend} Middle end
106 Puzzles has a single and universal \q{middle end}. This code is
107 common to all platforms and all games; it sits in between the front
108 end and the back end and provides standard functionality everywhere.
110 People adding new back ends or new front ends should generally not
111 need to edit the middle end. On rare occasions there might be a
112 change that can be made to the middle end to permit a new game to do
113 something not currently anticipated by the middle end's present
114 design; however, this is terribly easy to get wrong and should
115 probably not be undertaken without consulting the primary maintainer
116 (me). Patch submissions containing unannounced mid-end changes will
117 be treated on their merits like any other patch; this is just a
118 friendly warning that mid-end changes will need quite a lot of
119 merits to make them acceptable.
121 Functionality provided by the mid-end includes:
123 \b Maintaining a list of game state structures and moving back and
124 forth along that list to provide Undo and Redo.
126 \b Handling timers (for move animations, flashes on completion, and
127 in some cases actually timing the game).
129 \b Handling the container format of game IDs: receiving them,
130 picking them apart into parameters, description and/or random seed,
131 and so on. The game back end need only handle the individual parts
132 of a game ID (encoded parameters and encoded game description);
133 everything else is handled centrally by the mid-end.
135 \b Handling standard keystrokes and menu commands, such as \q{New
136 Game}, \q{Restart Game} and \q{Quit}.
138 \b Pre-processing mouse events so that the game back ends can rely
139 on them arriving in a sensible order (no missing button-release
140 events, no sudden changes of which button is currently pressed,
143 \b Handling the dialog boxes which ask the user for a game ID.
145 \b Handling serialisation of entire games (for loading and saving a
146 half-finished game to a disk file, or for handling application
147 shutdown and restart on platforms such as PalmOS where state is
148 expected to be saved).
150 Thus, there's a lot of work done once by the mid-end so that
151 individual back ends don't have to worry about it. All the back end
152 has to do is cooperate in ensuring the mid-end can do its work
155 The API of functions provided by the mid-end to be called by the
156 front end is documented in \k{midend}.
158 \H{intro-utils} Miscellaneous utilities
160 In addition to these three major structural components, the Puzzles
161 code also contains a variety of utility modules usable by all of the
162 above components. There is a set of functions to provide
163 platform-independent random number generation; functions to make
164 memory allocation easier; functions which implement a balanced tree
165 structure to be used as necessary in complex algorithms; and a few
166 other miscellaneous functions. All of these are documented in
169 \H{intro-structure} Structure of this guide
171 There are a number of function call interfaces within Puzzles, and
172 this guide will discuss each one in a chapter of its own. After
173 that, \k{writing} discusses how to design new games, with some
174 general design thoughts and tips.
176 \C{backend} Interface to the back end
178 This chapter gives a detailed discussion of the interface that each
179 back end must implement.
181 At the top level, each back end source file exports a single global
182 symbol, which is a \c{const struct game} containing a large number
183 of function pointers and a small amount of constant data. This
184 structure is called by different names depending on what kind of
185 platform the puzzle set is being compiled on:
187 \b On platforms such as Windows and GTK, which build a separate
188 binary for each puzzle, the game structure in every back end has the
189 same name, \cq{thegame}; the front end refers directly to this name,
190 so that compiling the same front end module against a different back
191 end module builds a different puzzle.
193 \b On platforms such as MacOS X and PalmOS, which build all the
194 puzzles into a single monolithic binary, the game structure in each
195 back end must have a different name, and there's a helper module
196 \c{list.c} (constructed automatically by the same Perl script that
197 builds the \cw{Makefile}s) which contains a complete list of those
200 On the latter type of platform, source files may assume that the
201 preprocessor symbol \c{COMBINED} has been defined. Thus, the usual
202 code to declare the game structure looks something like this:
205 \c #define thegame net /* or whatever this game is called */
206 \e iii iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii
209 \c const struct game thegame = {
210 \c /* lots of structure initialisation in here */
211 \e iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii
214 Game back ends must also internally define a number of data
215 structures, for storing their various persistent state. This chapter
216 will first discuss the nature and use of those structures, and then
217 go on to give details of every element of the game structure.
219 \H{backend-structs} Data structures
221 Each game is required to define four separate data structures. This
222 section discusses each one and suggests what sorts of things need to
225 \S{backend-game-params} \c{game_params}
227 The \c{game_params} structure contains anything which affects the
228 automatic generation of new puzzles. So if puzzle generation is
229 parametrised in any way, those parameters need to be stored in
232 Most puzzles currently in this collection are played on a grid of
233 squares, meaning that the most obvious parameter is the grid size.
234 Many puzzles have additional parameters; for example, Mines allows
235 you to control the number of mines in the grid independently of its
236 size, Net can be wrapping or non-wrapping, Solo has difficulty
237 levels and symmetry settings, and so on.
239 A simple rule for deciding whether a data item needs to go in
240 \c{game_params} is: would the user expect to be able to control this
241 data item from either the preset-game-types menu or the \q{Custom}
242 game type configuration? If so, it's part of \c{game_params}.
244 \c{game_params} structures are permitted to contain pointers to
245 subsidiary data if they need to. The back end is required to provide
246 functions to create and destroy \c{game_params}, and those functions
247 can allocate and free additional memory if necessary. (It has not
248 yet been necessary to do this in any puzzle so far, but the
249 capability is there just in case.)
251 \c{game_params} is also the only structure which the game's
252 \cw{compute_size()} function may refer to; this means that any
253 aspect of the game which affects the size of the window it needs to
254 be drawn in must be stored in \c{game_params}. In particular, this
255 imposes the fundamental limitation that random game generation may
256 not have a random effect on the window size: game generation
257 algorithms are constrained to work by starting from the grid size
258 rather than generating it as an emergent phenomenon. (Although this
259 is a restriction in theory, it has not yet seemed to be a problem.)
261 \S{backend-game-state} \c{game_state}
263 While the user is actually playing a puzzle, the \c{game_state}
264 structure stores all the data corresponding to the current state of
267 The mid-end keeps \c{game_state}s in a list, and adds to the list
268 every time the player makes a move; the Undo and Redo functions step
269 back and forth through that list.
271 Therefore, a good means of deciding whether a data item needs to go
272 in \c{game_state} is: would a player expect that data item to be
273 restored on undo? If so, put it in \c{game_state}, and this will
274 automatically happen without you having to lift a finger. If not
275 \dash for example, the deaths counter in Mines is precisely
276 something that does \e{not} want to be reset to its previous state
277 on an undo \dash then you might have found a data item that needs to
278 go in \c{game_ui} instead.
280 During play, \c{game_state}s are often passed around without an
281 accompanying \c{game_params} structure. Therefore, any information
282 in \c{game_params} which is important during play (such as the grid
283 size) must be duplicated within the \c{game_state}. One simple
284 method of doing this is to have the \c{game_state} structure
285 \e{contain} a \c{game_params} structure as one of its members,
286 although this isn't obligatory if you prefer to do it another way.
288 \S{backend-game-drawstate} \c{game_drawstate}
290 \c{game_drawstate} carries persistent state relating to the current
291 graphical contents of the puzzle window. The same \c{game_drawstate}
292 is passed to every call to the game redraw function, so that it can
293 remember what it has already drawn and what needs redrawing.
295 A typical use for a \c{game_drawstate} is to have an array mirroring
296 the array of grid squares in the \c{game_state}; then every time the
297 redraw function was passed a \c{game_state}, it would loop over all
298 the squares, and physically redraw any whose description in the
299 \c{game_state} (i.e. what the square needs to look like when the
300 redraw is completed) did not match its description in the
301 \c{game_drawstate} (i.e. what the square currently looks like).
303 \c{game_drawstate} is occasionally completely torn down and
304 reconstructed by the mid-end, if the user somehow forces a full
305 redraw. Therefore, no data should be stored in \c{game_drawstate}
306 which is \e{not} related to the state of the puzzle window, because
307 it might be unexpectedly destroyed.
309 The back end provides functions to create and destroy
310 \c{game_drawstate}, which means it can contain pointers to
311 subsidiary allocated data if it needs to. A common thing to want to
312 allocate in a \c{game_drawstate} is a \c{blitter}; see
313 \k{drawing-blitter} for more on this subject.
315 \S{backend-game-ui} \c{game_ui}
317 \c{game_ui} contains whatever doesn't fit into the above three
320 A new \c{game_ui} is created when the user begins playing a new
321 instance of a puzzle (i.e. during \q{New Game} or after entering a
322 game ID etc). It persists until the user finishes playing that game
323 and begins another one (or closes the window); in particular,
324 \q{Restart Game} does \e{not} destroy the \c{game_ui}.
326 \c{game_ui} is useful for implementing user-interface state which is
327 not part of \c{game_state}. Common examples are keyboard control
328 (you wouldn't want to have to separately Undo through every cursor
329 motion) and mouse dragging. See \k{writing-keyboard-cursor} and
330 \k{writing-howto-dragging}, respectively, for more details.
332 Another use for \c{game_ui} is to store highly persistent data such
333 as the Mines death counter. This is conceptually rather different:
334 where the Net cursor position was \e{not important enough} to
335 preserve for the player to restore by Undo, the Mines death counter
336 is \e{too important} to permit the player to revert by Undo!
338 A final use for \c{game_ui} is to pass information to the redraw
339 function about recent changes to the game state. This is used in
340 Mines, for example, to indicate whether a requested \q{flash} should
341 be a white flash for victory or a red flash for defeat; see
342 \k{writing-flash-types}.
344 \H{backend-simple} Simple data in the back end
346 In this section I begin to discuss each individual element in the
347 back end structure. To begin with, here are some simple
348 self-contained data elements.
350 \S{backend-name} \c{name}
354 This is a simple ASCII string giving the name of the puzzle. This
355 name will be used in window titles, in game selection menus on
356 monolithic platforms, and anywhere else that the front end needs to
357 know the name of a game.
359 \S{backend-winhelp} \c{winhelp_topic}
361 \c const char *winhelp_topic;
363 This member is used on Windows only, to provide online help.
364 Although the Windows front end provides a separate binary for each
365 puzzle, it has a single monolithic help file; so when a user selects
366 \q{Help} from the menu, the program needs to open the help file and
367 jump to the chapter describing that particular puzzle.
369 Therefore, each chapter in \c{puzzles.but} is labelled with a
370 \e{help topic} name, similar to this:
372 \c \cfg{winhelp-topic}{games.net}
374 And then the corresponding game back end encodes the topic string
375 (here \cq{games.net}) in the \c{winhelp_topic} element of the game
378 \H{backend-params} Handling game parameter sets
380 In this section I present the various functions which handle the
381 \c{game_params} structure.
383 \S{backend-default-params} \cw{default_params()}
385 \c game_params *(*default_params)(void);
387 This function allocates a new \c{game_params} structure, fills it
388 with the default values, and returns a pointer to it.
390 \S{backend-fetch-preset} \cw{fetch_preset()}
392 \c int (*fetch_preset)(int i, char **name, game_params **params);
394 This function is used to populate the \q{Type} menu, which provides
395 a list of conveniently accessible preset parameters for most games.
397 The function is called with \c{i} equal to the index of the preset
398 required (numbering from zero). It returns \cw{FALSE} if that preset
399 does not exist (if \c{i} is less than zero or greater than the
400 largest preset index). Otherwise, it sets \c{*params} to point at a
401 newly allocated \c{game_params} structure containing the preset
402 information, sets \c{*name} to point at a newly allocated C string
403 containing the preset title (to go on the \q{Type} menu), and
406 If the game does not wish to support any presets at all, this
407 function is permitted to return \cw{FALSE} always.
409 \S{backend-encode-params} \cw{encode_params()}
411 \c char *(*encode_params)(game_params *params, int full);
413 The job of this function is to take a \c{game_params}, and encode it
414 in a string form for use in game IDs. The return value must be a
415 newly allocated C string, and \e{must} not contain a colon or a hash
416 (since those characters are used to mark the end of the parameter
417 section in a game ID).
419 Ideally, it should also not contain any other potentially
420 controversial punctuation; bear in mind when designing a string
421 parameter format that it will probably be used on both Windows and
422 Unix command lines under a variety of exciting shell quoting and
423 metacharacter rules. Sticking entirely to alphanumerics is the
424 safest thing; if you really need punctuation, you can probably get
425 away with commas, periods or underscores without causing anybody any
426 major inconvenience. If you venture far beyond that, you're likely
427 to irritate \e{somebody}.
429 (At the time of writing this, all existing games have purely
430 alphanumeric string parameter formats. Usually these involve a
431 letter denoting a parameter, followed optionally by a number giving
432 the value of that parameter, with a few mandatory parts at the
433 beginning such as numeric width and height separated by \cq{x}.)
435 If the \c{full} parameter is \cw{TRUE}, this function should encode
436 absolutely everything in the \c{game_params}, such that a subsequent
437 call to \cw{decode_params()} (\k{backend-decode-params}) will yield
438 an identical structure. If \c{full} is \cw{FALSE}, however, you
439 should leave out anything which is not necessary to describe a
440 \e{specific puzzle instance}, i.e. anything which only takes effect
441 when a new puzzle is \e{generated}. For example, the Solo
442 \c{game_params} includes a difficulty rating used when constructing
443 new puzzles; but a Solo game ID need not explicitly include the
444 difficulty, since to describe a puzzle once generated it's
445 sufficient to give the grid dimensions and the location and contents
446 of the clue squares. (Indeed, one might very easily type in a puzzle
447 out of a newspaper without \e{knowing} what its difficulty level is
448 in Solo's terminology.) Therefore, Solo's \cw{encode_params()} only
449 encodes the difficulty level if \c{full} is set.
451 \S{backend-decode-params} \cw{decode_params()}
453 \c void (*decode_params)(game_params *params, char const *string);
455 This function is the inverse of \cw{encode_params()}
456 (\k{backend-encode-params}). It parses the supplied string and fills
457 in the supplied \c{game_params} structure. Note that the structure
458 will \e{already} have been allocated: this function is not expected
459 to create a \e{new} \c{game_params}, but to modify an existing one.
461 This function can receive a string which only encodes a subset of
462 the parameters. The most obvious way in which this can happen is if
463 the string was constructed by \cw{encode_params()} with its \c{full}
464 parameter set to \cw{FALSE}; however, it could also happen if the
465 user typed in a parameter set manually and missed something out. Be
466 prepared to deal with a wide range of possibilities.
468 When dealing with a parameter which is not specified in the input
469 string, what to do requires a judgment call on the part of the
470 programmer. Sometimes it makes sense to adjust other parameters to
471 bring them into line with the new ones. In Mines, for example, you
472 would probably not want to keep the same mine count if the user
473 dropped the grid size and didn't specify one, since you might easily
474 end up with more mines than would actually fit in the grid! On the
475 other hand, sometimes it makes sense to leave the parameter alone: a
476 Solo player might reasonably expect to be able to configure size and
477 difficulty independently of one another.
479 This function currently has no direct means of returning an error if
480 the string cannot be parsed at all. However, the returned
481 \c{game_params} is almost always subsequently passed to
482 \cw{validate_params()} (\k{backend-validate-params}), so if you
483 really want to signal parse errors, you could always have a \c{char
484 *} in your parameters structure which stored an error message, and
485 have \cw{validate_params()} return it if it is non-\cw{NULL}.
487 \S{backend-free-params} \cw{free_params()}
489 \c void (*free_params)(game_params *params);
491 This function frees a \c{game_params} structure, and any subsidiary
492 allocations contained within it.
494 \S{backend-dup-params} \cw{dup_params()}
496 \c game_params *(*dup_params)(game_params *params);
498 This function allocates a new \c{game_params} structure and
499 initialises it with an exact copy of the information in the one
500 provided as input. It returns a pointer to the new duplicate.
502 \S{backend-can-configure} \c{can_configure}
504 \c int can_configure;
506 This boolean data element is set to \cw{TRUE} if the back end
507 supports custom parameter configuration via a dialog box. If it is
508 \cw{TRUE}, then the functions \cw{configure()} and
509 \cw{custom_params()} are expected to work. See \k{backend-configure}
510 and \k{backend-custom-params} for more details.
512 \S{backend-configure} \cw{configure()}
514 \c config_item *(*configure)(game_params *params);
516 This function is called when the user requests a dialog box for
517 custom parameter configuration. It returns a newly allocated array
518 of \cw{config_item} structures, describing the GUI elements required
519 in the dialog box. The array should have one more element than the
520 number of controls, since it is terminated with a \cw{C_END} marker
521 (see below). Each array element describes the control together with
522 its initial value; the front end will modify the value fields and
523 return the updated array to \cw{custom_params()} (see
524 \k{backend-custom-params}).
526 The \cw{config_item} structure contains the following elements:
533 \c{name} is an ASCII string giving the textual label for a GUI
534 control. It is \e{not} expected to be dynamically allocated.
536 \c{type} contains one of a small number of \c{enum} values defining
537 what type of control is being described. The meaning of the \c{sval}
538 and \c{ival} fields depends on the value in \c{type}. The valid
543 \dd Describes a text input box. (This is also used for numeric
544 input. The back end does not bother informing the front end that the
545 box is numeric rather than textual; some front ends do have the
546 capacity to take this into account, but I decided it wasn't worth
547 the extra complexity in the interface.) For this type, \c{ival} is
548 unused, and \c{sval} contains a dynamically allocated string
549 representing the contents of the input box.
553 \dd Describes a simple checkbox. For this type, \c{sval} is unused,
554 and \c{ival} is \cw{TRUE} or \cw{FALSE}.
558 \dd Describes a drop-down list presenting one of a small number of
559 fixed choices. For this type, \c{sval} contains a list of strings
560 describing the choices; the very first character of \c{sval} is used
561 as a delimiter when processing the rest (so that the strings
562 \cq{:zero:one:two}, \cq{!zero!one!two} and \cq{xzeroxonextwo} all
563 define a three-element list containing \cq{zero}, \cq{one} and
564 \cq{two}). \c{ival} contains the index of the currently selected
565 element, numbering from zero (so that in the above example, 0 would
566 mean \cq{zero} and 2 would mean \cq{two}).
570 Note that for this control type, \c{sval} is \e{not} dynamically
571 allocated, whereas it was for \c{C_STRING}.
577 \dd Marks the end of the array of \c{config_item}s. All other fields
580 The array returned from this function is expected to have filled in
581 the initial values of all the controls according to the input
582 \c{game_params} structure.
584 If the game's \c{can_configure} flag is set to \cw{FALSE}, this
585 function is never called and need not do anything at all.
587 \S{backend-custom-params} \cw{custom_params()}
589 \c game_params *(*custom_params)(config_item *cfg);
591 This function is the counterpart to \cw{configure()}
592 (\k{backend-configure}). It receives as input an array of
593 \c{config_item}s which was originally created by \cw{configure()},
594 but in which the control values have since been changed in
595 accordance with user input. Its function is to read the new values
596 out of the controls and return a newly allocated \c{game_params}
597 structure representing the user's chosen parameter set.
599 (The front end will have modified the controls' \e{values}, but
600 there will still always be the same set of controls, in the same
601 order, as provided by \cw{configure()}. It is not necessary to check
602 the \c{name} and \c{type} fields, although you could use
603 \cw{assert()} if you were feeling energetic.)
605 This function is not expected to (and indeed \e{must not}) free the
606 input \c{config_item} array. (If the parameters fail to validate,
607 the dialog box will stay open.)
609 If the game's \c{can_configure} flag is set to \cw{FALSE}, this
610 function is never called and need not do anything at all.
612 \S{backend-validate-params} \cw{validate_params()}
614 \c char *(*validate_params)(game_params *params, int full);
616 This function takes a \c{game_params} structure as input, and checks
617 that the parameters described in it fall within sensible limits. (At
618 the very least, grid dimensions should almost certainly be strictly
619 positive, for example.)
621 Return value is \cw{NULL} if no problems were found, or
622 alternatively a (non-dynamically-allocated) ASCII string describing
623 the error in human-readable form.
625 If the \c{full} parameter is set, full validation should be
626 performed: any set of parameters which would not permit generation
627 of a sensible puzzle should be faulted. If \c{full} is \e{not} set,
628 the implication is that these parameters are not going to be used
629 for \e{generating} a puzzle; so parameters which can't even sensibly
630 \e{describe} a valid puzzle should still be faulted, but parameters
631 which only affect puzzle generation should not be.
633 (The \c{full} option makes a difference when parameter combinations
634 are non-orthogonal. For example, Net has a boolean option
635 controlling whether it enforces a unique solution; it turns out that
636 it's impossible to generate a uniquely soluble puzzle with wrapping
637 walls and width 2, so \cw{validate_params()} will complain if you
638 ask for one. However, if the user had just been playing a unique
639 wrapping puzzle of a more sensible width, and then pastes in a game
640 ID acquired from somebody else which happens to describe a
641 \e{non}-unique wrapping width-2 puzzle, then \cw{validate_params()}
642 will be passed a \c{game_params} containing the width and wrapping
643 settings from the new game ID and the uniqueness setting from the
644 old one. This would be faulted, if it weren't for the fact that
645 \c{full} is not set during this call, so Net ignores the
646 inconsistency. The resulting \c{game_params} is never subsequently
647 used to generate a puzzle; this is a promise made by the mid-end
648 when it asks for a non-full validation.)
650 \H{backend-descs} Handling game descriptions
652 In this section I present the functions that deal with a textual
653 description of a puzzle, i.e. the part that comes after the colon in
654 a descriptive-format game ID.
656 \S{backend-new-desc} \cw{new_desc()}
658 \c char *(*new_desc)(game_params *params, random_state *rs,
659 \c char **aux, int interactive);
661 This function is where all the really hard work gets done. This is
662 the function whose job is to randomly generate a new puzzle,
663 ensuring solubility and uniqueness as appropriate.
665 As input it is given a \c{game_params} structure and a random state
666 (see \k{utils-random} for the random number API). It must invent a
667 puzzle instance, encode it in string form, and return a dynamically
668 allocated C string containing that encoding.
670 Additionally, it may return a second dynamically allocated string in
671 \c{*aux}. (If it doesn't want to, then it can leave that parameter
672 completely alone; it isn't required to set it to \cw{NULL}, although
673 doing so is harmless.) That string, if present, will be passed to
674 \cw{solve()} (\k{backend-solve}) later on; so if the puzzle is
675 generated in such a way that a solution is known, then information
676 about that solution can be saved in \c{*aux} for \cw{solve()} to
679 The \c{interactive} parameter should be ignored by almost all
680 puzzles. Its purpose is to distinguish between generating a puzzle
681 within a GUI context for immediate play, and generating a puzzle in
682 a command-line context for saving to be played later. The only
683 puzzle that currently uses this distinction (and, I fervently hope,
684 the only one which will \e{ever} need to use it) is Mines, which
685 chooses a random first-click location when generating puzzles
686 non-interactively, but which waits for the user to place the first
687 click when interactive. If you think you have come up with another
688 puzzle which needs to make use of this parameter, please think for
689 at least ten minutes about whether there is \e{any} alternative!
691 Note that game description strings are not required to contain an
692 encoding of parameters such as grid size; a game description is
693 never separated from the \c{game_params} it was generated with, so
694 any information contained in that structure need not be encoded
695 again in the game description.
697 \S{backend-validate-desc} \cw{validate_desc()}
699 \c char *(*validate_desc)(game_params *params, char *desc);
701 This function is given a game description, and its job is to
702 validate that it describes a puzzle which makes sense.
704 To some extent it's up to the user exactly how far they take the
705 phrase \q{makes sense}; there are no particularly strict rules about
706 how hard the user is permitted to shoot themself in the foot when
707 typing in a bogus game description by hand. (For example, Rectangles
708 will not verify that the sum of all the numbers in the grid equals
709 the grid's area. So a user could enter a puzzle which was provably
710 not soluble, and the program wouldn't complain; there just wouldn't
711 happen to be any sequence of moves which solved it.)
713 The one non-negotiable criterion is that any game description which
714 makes it through \cw{validate_desc()} \e{must not} subsequently
715 cause a crash or an assertion failure when fed to \cw{new_game()}
716 and thence to the rest of the back end.
718 The return value is \cw{NULL} on success, or a
719 non-dynamically-allocated C string containing an error message.
721 \S{backend-new-game} \cw{new_game()}
723 \c game_state *(*new_game)(midend *me, game_params *params,
726 This function takes a game description as input, together with its
727 accompanying \c{game_params}, and constructs a \c{game_state}
728 describing the initial state of the puzzle. It returns a newly
729 allocated \c{game_state} structure.
731 Almost all puzzles should ignore the \c{me} parameter. It is
732 required by Mines, which needs it for later passing to
733 \cw{midend_supersede_game_desc()} (see \k{backend-supersede}) once
734 the user has placed the first click. I fervently hope that no other
735 puzzle will be awkward enough to require it, so everybody else
736 should ignore it. As with the \c{interactive} parameter in
737 \cw{new_desc()} (\k{backend-new-desc}), if you think you have a
738 reason to need this parameter, please try very hard to think of an
739 alternative approach!
741 \H{backend-states} Handling game states
743 This section describes the functions which create and destroy
744 \c{game_state} structures.
746 (Well, except \cw{new_game()}, which is in \k{backend-new-game}
747 instead of under here; but it deals with game descriptions \e{and}
748 game states and it had to go in one section or the other.)
750 \S{backend-dup-game} \cw{dup_game()}
752 \c game_state *(*dup_game)(game_state *state);
754 This function allocates a new \c{game_state} structure and
755 initialises it with an exact copy of the information in the one
756 provided as input. It returns a pointer to the new duplicate.
758 \S{backend-free-game} \cw{free_game()}
760 \c void (*free_game)(game_state *state);
762 This function frees a \c{game_state} structure, and any subsidiary
763 allocations contained within it.
765 \H{backend-ui} Handling \c{game_ui}
767 \S{backend-new-ui} \cw{new_ui()}
769 \c game_ui *(*new_ui)(game_state *state);
771 This function allocates and returns a new \c{game_ui} structure for
772 playing a particular puzzle. It is passed a pointer to the initial
773 \c{game_state}, in case it needs to refer to that when setting up
774 the initial values for the new game.
776 \S{backend-free-ui} \cw{free_ui()}
778 \c void (*free_ui)(game_ui *ui);
780 This function frees a \c{game_ui} structure, and any subsidiary
781 allocations contained within it.
783 \S{backend-encode-ui} \cw{encode_ui()}
785 \c char *(*encode_ui)(game_ui *ui);
787 This function encodes any \e{important} data in a \c{game_ui}
788 structure in string form. It is only called when saving a
789 half-finished game to a file.
791 It should be used sparingly. Almost all data in a \c{game_ui} is not
792 important enough to save. The location of the keyboard-controlled
793 cursor, for example, can be reset to a default position on reloading
794 the game without impacting the user experience. If the user should
795 somehow manage to save a game while a mouse drag was in progress,
796 then discarding that mouse drag would be an outright \e{feature}.
798 A typical thing that \e{would} be worth encoding in this function is
799 the Mines death counter: it's in the \c{game_ui} rather than the
800 \c{game_state} because it's too important to allow the user to
801 revert it by using Undo, and therefore it's also too important to
802 allow the user to revert it by saving and reloading. (Of course, the
803 user could edit the save file by hand... But if the user is \e{that}
804 determined to cheat, they could just as easily modify the game's
807 \S{backend-decode-ui} \cw{decode_ui()}
809 \c void (*decode_ui)(game_ui *ui, char *encoding);
811 This function parses a string previously output by \cw{encode_ui()},
812 and writes the decoded data back into the provided \c{game_ui}
815 \S{backend-changed-state} \cw{changed_state()}
817 \c void (*changed_state)(game_ui *ui, game_state *oldstate,
818 \c game_state *newstate);
820 This function is called by the mid-end whenever the current game
821 state changes, for any reason. Those reasons include:
823 \b a fresh move being made by \cw{interpret_move()} and
826 \b a solve operation being performed by \cw{solve()} and
829 \b the user moving back and forth along the undo list by means of
830 the Undo and Redo operations
832 \b the user selecting Restart to go back to the initial game state.
834 The job of \cw{changed_state()} is to update the \c{game_ui} for
835 consistency with the new game state, if any update is necessary. For
836 example, Same Game stores data about the currently selected tile
837 group in its \c{game_ui}, and this data is intrinsically related to
838 the game state it was derived from. So it's very likely to become
839 invalid when the game state changes; thus, Same Game's
840 \cw{changed_state()} function clears the current selection whenever
843 When \cw{anim_length()} or \cw{flash_length()} are called, you can
844 be sure that there has been a previous call to \cw{changed_state()}.
845 So \cw{changed_state()} can set up data in the \c{game_ui} which will
846 be read by \cw{anim_length()} and \cw{flash_length()}, and those
847 functions will not have to worry about being called without the data
848 having been initialised.
850 \H{backend-moves} Making moves
852 This section describes the functions which actually make moves in
853 the game: that is, the functions which process user input and end up
854 producing new \c{game_state}s.
856 \S{backend-interpret-move} \cw{interpret_move()}
858 \c char *(*interpret_move)(game_state *state, game_ui *ui,
859 \c game_drawstate *ds,
860 \c int x, int y, int button);
862 This function receives user input and processes it. Its input
863 parameters are the current \c{game_state}, the current \c{game_ui}
864 and the current \c{game_drawstate}, plus details of the input event.
865 \c{button} is either an ASCII value or a special code (listed below)
866 indicating an arrow or function key or a mouse event; when
867 \c{button} is a mouse event, \c{x} and \c{y} contain the pixel
868 coordinates of the mouse pointer relative to the top left of the
869 puzzle's drawing area.
871 \cw{interpret_move()} may return in three different ways:
873 \b Returning \cw{NULL} indicates that no action whatsoever occurred
874 in response to the input event; the puzzle was not interested in it
877 \b Returning the empty string (\cw{""}) indicates that the input
878 event has resulted in a change being made to the \c{game_ui} which
879 will require a redraw of the game window, but that no actual
880 \e{move} was made (i.e. no new \c{game_state} needs to be created).
882 \b Returning anything else indicates that a move was made and that a
883 new \c{game_state} must be created. However, instead of actually
884 constructing a new \c{game_state} itself, this function is required
885 to return a string description of the details of the move. This
886 string will be passed to \cw{execute_move()}
887 (\k{backend-execute-move}) to actually create the new
888 \c{game_state}. (Encoding moves as strings in this way means that
889 the mid-end can keep the strings as well as the game states, and the
890 strings can be written to disk when saving the game and fed to
891 \cw{execute_move()} again on reloading.)
893 The return value from \cw{interpret_move()} is expected to be
894 dynamically allocated if and only if it is not either \cw{NULL}
895 \e{or} the empty string.
897 After this function is called, the back end is permitted to rely on
898 some subsequent operations happening in sequence:
900 \b \cw{execute_move()} will be called to convert this move
901 description into a new \c{game_state}
903 \b \cw{changed_state()} will be called with the new \c{game_state}.
905 This means that if \cw{interpret_move()} needs to do updates to the
906 \c{game_ui} which are easier to perform by referring to the new
907 \c{game_state}, it can safely leave them to be done in
908 \cw{changed_state()} and not worry about them failing to happen.
910 (Note, however, that \cw{execute_move()} may \e{also} be called in
911 other circumstances. It is only \cw{interpret_move()} which can rely
912 on a subsequent call to \cw{changed_state()}.)
914 The special key codes supported by this function are:
916 \dt \cw{LEFT_BUTTON}, \cw{MIDDLE_BUTTON}, \cw{RIGHT_BUTTON}
918 \dd Indicate that one of the mouse buttons was pressed down.
920 \dt \cw{LEFT_DRAG}, \cw{MIDDLE_DRAG}, \cw{RIGHT_DRAG}
922 \dd Indicate that the mouse was moved while one of the mouse buttons
923 was still down. The mid-end guarantees that when one of these events
924 is received, it will always have been preceded by a button-down
925 event (and possibly other drag events) for the same mouse button,
926 and no event involving another mouse button will have appeared in
929 \dt \cw{LEFT_RELEASE}, \cw{MIDDLE_RELEASE}, \cw{RIGHT_RELEASE}
931 \dd Indicate that a mouse button was released. The mid-end
932 guarantees that when one of these events is received, it will always
933 have been preceded by a button-down event (and possibly some drag
934 events) for the same mouse button, and no event involving another
935 mouse button will have appeared in between.
937 \dt \cw{CURSOR_UP}, \cw{CURSOR_DOWN}, \cw{CURSOR_LEFT},
940 \dd Indicate that an arrow key was pressed.
942 \dt \cw{CURSOR_SELECT}
944 \dd On platforms which have a prominent \q{select} button alongside
945 their cursor keys, indicates that that button was pressed.
947 In addition, there are some modifiers which can be bitwise-ORed into
948 the \c{button} parameter:
950 \dt \cw{MOD_CTRL}, \cw{MOD_SHFT}
952 \dd These indicate that the Control or Shift key was pressed
953 alongside the key. They only apply to the cursor keys, not to mouse
954 buttons or anything else.
956 \dt \cw{MOD_NUM_KEYPAD}
958 \dd This applies to some ASCII values, and indicates that the key
959 code was input via the numeric keypad rather than the main keyboard.
960 Some puzzles may wish to treat this differently (for example, a
961 puzzle might want to use the numeric keypad as an eight-way
962 directional pad), whereas others might not (a game involving numeric
963 input probably just wants to treat the numeric keypad as numbers).
967 \dd This mask is the bitwise OR of all the available modifiers; you
968 can bitwise-AND with \cw{~MOD_MASK} to strip all the modifiers off
971 \S{backend-execute-move} \cw{execute_move()}
973 \c game_state *(*execute_move)(game_state *state, char *move);
975 This function takes an input \c{game_state} and a move string as
976 output from \cw{interpret_move()}. It returns a newly allocated
977 \c{game_state} which contains the result of applying the specified
978 move to the input game state.
980 This function may return \cw{NULL} if it cannot parse the move
981 string (and this is definitely preferable to crashing or failing an
982 assertion, since one way this can happen is if loading a corrupt
983 save file). However, it must not return \cw{NULL} for any move
984 string that really was output from \cw{interpret_move()}: this is
985 punishable by assertion failure in the mid-end.
987 \S{backend-can-solve} \c{can_solve}
991 This boolean field is set to \cw{TRUE} if the game's \cw{solve()}
992 function does something. If it's set to \cw{FALSE}, the game will
993 not even offer the \q{Solve} menu option.
995 \S{backend-solve} \cw{solve()}
997 \c char *(*solve)(game_state *orig, game_state *curr,
998 \c char *aux, char **error);
1000 This function is called when the user selects the \q{Solve} option
1003 It is passed two input game states: \c{orig} is the game state from
1004 the very start of the puzzle, and \c{curr} is the current one.
1005 (Different games find one or other or both of these convenient.) It
1006 is also passed the \c{aux} string saved by \cw{new_desc()}
1007 (\k{backend-new-desc}), in case that encodes important information
1008 needed to provide the solution.
1010 If this function is unable to produce a solution (perhaps, for
1011 example, the game has no in-built solver so it can only solve
1012 puzzles it invented internally and has an \c{aux} string for) then
1013 it may return \cw{NULL}. If it does this, it must also set
1014 \c{*error} to an error message to be presented to the user (such as
1015 \q{Solution not known for this puzzle}); that error message is not
1016 expected to be dynamically allocated.
1018 If this function \e{does} produce a solution, it returns a move
1019 string suitable for feeding to \cw{execute_move()}
1020 (\k{backend-execute-move}).
1022 \H{backend-drawing} Drawing the game graphics
1024 This section discusses the back end functions that deal with
1027 \S{backend-new-drawstate} \cw{new_drawstate()}
1029 \c game_drawstate *(*new_drawstate)(drawing *dr, game_state *state);
1031 This function allocates and returns a new \c{game_drawstate}
1032 structure for drawing a particular puzzle. It is passed a pointer to
1033 a \c{game_state}, in case it needs to refer to that when setting up
1036 This function may not rely on the puzzle having been newly started;
1037 a new draw state can be constructed at any time if the front end
1038 requests a forced redraw. For games like Pattern, in which initial
1039 game states are much simpler than general ones, this might be
1040 important to keep in mind.
1042 The parameter \c{dr} is a drawing object (see \k{drawing}) which the
1043 function might need to use to allocate blitters. (However, this
1044 isn't recommended; it's usually more sensible to wait to allocate a
1045 blitter until \cw{set_size()} is called, because that way you can
1046 tailor it to the scale at which the puzzle is being drawn.)
1048 \S{backend-free-drawstate} \cw{free_drawstate()}
1050 \c void (*free_drawstate)(drawing *dr, game_drawstate *ds);
1052 This function frees a \c{game_drawstate} structure, and any
1053 subsidiary allocations contained within it.
1055 The parameter \c{dr} is a drawing object (see \k{drawing}), which
1056 might be required if you are freeing a blitter.
1058 \S{backend-preferred-tilesize} \c{preferred_tilesize}
1060 \c int preferred_tilesize;
1062 Each game is required to define a single integer parameter which
1063 expresses, in some sense, the scale at which it is drawn. This is
1064 described in the APIs as \cq{tilesize}, since most puzzles are on a
1065 square (or possibly triangular or hexagonal) grid and hence a
1066 sensible interpretation of this parameter is to define it as the
1067 size of one grid tile in pixels; however, there's no actual
1068 requirement that the \q{tile size} be proportional to the game
1069 window size. Window size is required to increase monotonically with
1070 \q{tile size}, however.
1072 The data element \c{preferred_tilesize} indicates the tile size
1073 which should be used in the absence of a good reason to do otherwise
1074 (such as the screen being too small, or the user explicitly
1075 requesting a resize if that ever gets implemented).
1077 \S{backend-compute-size} \cw{compute_size()}
1079 \c void (*compute_size)(game_params *params, int tilesize,
1082 This function is passed a \c{game_params} structure and a tile size.
1083 It returns, in \c{*x} and \c{*y}, the size in pixels of the drawing
1084 area that would be required to render a puzzle with those parameters
1087 \S{backend-set-size} \cw{set_size()}
1089 \c void (*set_size)(drawing *dr, game_drawstate *ds,
1090 \c game_params *params, int tilesize);
1092 This function is responsible for setting up a \c{game_drawstate} to
1093 draw at a given tile size. Typically this will simply involve
1094 copying the supplied \c{tilesize} parameter into a \c{tilesize}
1095 field inside the draw state; for some more complex games it might
1096 also involve setting up other dimension fields, or possibly
1097 allocating a blitter (see \k{drawing-blitter}).
1099 The parameter \c{dr} is a drawing object (see \k{drawing}), which is
1100 required if a blitter needs to be allocated.
1102 Back ends may assume (and may enforce by assertion) that this
1103 function will be called at most once for any \c{game_drawstate}. If
1104 a puzzle needs to be redrawn at a different size, the mid-end will
1105 create a fresh drawstate.
1107 \S{backend-colours} \cw{colours()}
1109 \c float *(*colours)(frontend *fe, int *ncolours);
1111 This function is responsible for telling the front end what colours
1112 the puzzle will need to draw itself.
1114 It returns the number of colours required in \c{*ncolours}, and the
1115 return value from the function itself is a dynamically allocated
1116 array of three times that many \c{float}s, containing the red, green
1117 and blue components of each colour respectively as numbers in the
1120 The second parameter passed to this function is a front end handle.
1121 The only things it is permitted to do with this handle are to call
1122 the front-end function called \cw{frontend_default_colour()} (see
1123 \k{frontend-default-colour}) or the utility function called
1124 \cw{game_mkhighlight()} (see \k{utils-game-mkhighlight}). (The
1125 latter is a wrapper on the former, so front end implementors only
1126 need to provide \cw{frontend_default_colour()}.) This allows
1127 \cw{colours()} to take local configuration into account when
1128 deciding on its own colour allocations. Most games use the front
1129 end's default colour as their background, apart from a few which
1130 depend on drawing relief highlights so they adjust the background
1131 colour if it's too light for highlights to show up against it.
1133 Note that the colours returned from this function are for
1134 \e{drawing}, not for printing. Printing has an entirely different
1135 colour allocation policy.
1137 \S{backend-anim-length} \cw{anim_length()}
1139 \c float (*anim_length)(game_state *oldstate, game_state *newstate,
1140 \c int dir, game_ui *ui);
1142 This function is called when a move is made, undone or redone. It is
1143 given the old and the new \c{game_state}, and its job is to decide
1144 whether the transition between the two needs to be animated or can
1147 \c{oldstate} is the state that was current until this call;
1148 \c{newstate} is the state that will be current after it. \c{dir}
1149 specifies the chronological order of those states: if it is
1150 positive, then the transition is the result of a move or a redo (and
1151 so \c{newstate} is the later of the two moves), whereas if it is
1152 negative then the transition is the result of an undo (so that
1153 \c{newstate} is the \e{earlier} move).
1155 If this function decides the transition should be animated, it
1156 returns the desired length of the animation in seconds. If not, it
1159 State changes as a result of a Restart operation are never animated;
1160 the mid-end will handle them internally and never consult this
1161 function at all. State changes as a result of Solve operations are
1162 also not animated by default, although you can change this for a
1163 particular game by setting a flag in \c{flags} (\k{backend-flags}).
1165 The function is also passed a pointer to the local \c{game_ui}. It
1166 may refer to information in here to help with its decision (see
1167 \k{writing-conditional-anim} for an example of this), and/or it may
1168 \e{write} information about the nature of the animation which will
1169 be read later by \cw{redraw()}.
1171 When this function is called, it may rely on \cw{changed_state()}
1172 having been called previously, so if \cw{anim_length()} needs to
1173 refer to information in the \c{game_ui}, then \cw{changed_state()}
1174 is a reliable place to have set that information up.
1176 Move animations do not inhibit further input events. If the user
1177 continues playing before a move animation is complete, the animation
1178 will be abandoned and the display will jump straight to the final
1181 \S{backend-flash-length} \cw{flash_length()}
1183 \c float (*flash_length)(game_state *oldstate, game_state *newstate,
1184 \c int dir, game_ui *ui);
1186 This function is called when a move is completed. (\q{Completed}
1187 means that not only has the move been made, but any animation which
1188 accompanied it has finished.) It decides whether the transition from
1189 \c{oldstate} to \c{newstate} merits a \q{flash}.
1191 A flash is much like a move animation, but it is \e{not} interrupted
1192 by further user interface activity; it runs to completion in
1193 parallel with whatever else might be going on on the display. The
1194 only thing which will rush a flash to completion is another flash.
1196 The purpose of flashes is to indicate that the game has been
1197 completed. They were introduced as a separate concept from move
1198 animations because of Net: the habit of most Net players (and
1199 certainly me) is to rotate a tile into place and immediately lock
1200 it, then move on to another tile. When you make your last move, at
1201 the instant the final tile is rotated into place the screen starts
1202 to flash to indicate victory \dash but if you then press the lock
1203 button out of habit, then the move animation is cancelled, and the
1204 victory flash does not complete. (And if you \e{don't} press the
1205 lock button, the completed grid will look untidy because there will
1206 be one unlocked square.) Therefore, I introduced a specific concept
1207 of a \q{flash} which is separate from a move animation and can
1208 proceed in parallel with move animations and any other display
1209 activity, so that the victory flash in Net is not cancelled by that
1212 The input parameters to \cw{flash_length()} are exactly the same as
1213 the ones to \cw{anim_length()}.
1215 Just like \cw{anim_length()}, when this function is called, it may
1216 rely on \cw{changed_state()} having been called previously, so if it
1217 needs to refer to information in the \c{game_ui} then
1218 \cw{changed_state()} is a reliable place to have set that
1221 (Some games use flashes to indicate defeat as well as victory;
1222 Mines, for example, flashes in a different colour when you tread on
1223 a mine from the colour it uses when you complete the game. In order
1224 to achieve this, its \cw{flash_length()} function has to store a
1225 flag in the \c{game_ui} to indicate which flash type is required.)
1227 \S{backend-redraw} \cw{redraw()}
1229 \c void (*redraw)(drawing *dr, game_drawstate *ds,
1230 \c game_state *oldstate, game_state *newstate, int dir,
1231 \c game_ui *ui, float anim_time, float flash_time);
1233 This function is responsible for actually drawing the contents of
1234 the game window, and for redrawing every time the game state or the
1235 \c{game_ui} changes.
1237 The parameter \c{dr} is a drawing object which may be passed to the
1238 drawing API functions (see \k{drawing} for documentation of the
1239 drawing API). This function may not save \c{dr} and use it
1240 elsewhere; it must only use it for calling back to the drawing API
1241 functions within its own lifetime.
1243 \c{ds} is the local \c{game_drawstate}, of course, and \c{ui} is the
1246 \c{newstate} is the semantically-current game state, and is always
1247 non-\cw{NULL}. If \c{oldstate} is also non-\cw{NULL}, it means that
1248 a move has recently been made and the game is still in the process
1249 of displaying an animation linking the old and new states; in this
1250 situation, \c{anim_time} will give the length of time (in seconds)
1251 that the animation has already been running. If \c{oldstate} is
1252 \cw{NULL}, then \c{anim_time} is unused (and will hopefully be set
1253 to zero to avoid confusion).
1255 \c{flash_time}, if it is is non-zero, denotes that the game is in
1256 the middle of a flash, and gives the time since the start of the
1257 flash. See \k{backend-flash-length} for general discussion of
1260 The very first time this function is called for a new
1261 \c{game_drawstate}, it is expected to redraw the \e{entire} drawing
1262 area. Since this often involves drawing visual furniture which is
1263 never subsequently altered, it is often simplest to arrange this by
1264 having a special \q{first time} flag in the draw state, and
1265 resetting it after the first redraw.
1267 When this function (or any subfunction) calls the drawing API, it is
1268 expected to pass colour indices which were previously defined by the
1269 \cw{colours()} function.
1271 \H{backend-printing} Printing functions
1273 This section discusses the back end functions that deal with
1274 printing puzzles out on paper.
1276 \S{backend-can-print} \c{can_print}
1280 This flag is set to \cw{TRUE} if the puzzle is capable of printing
1281 itself on paper. (This makes sense for some puzzles, such as Solo,
1282 which can be filled in with a pencil. Other puzzles, such as
1283 Twiddle, inherently involve moving things around and so would not
1284 make sense to print.)
1286 If this flag is \cw{FALSE}, then the functions \cw{print_size()}
1287 and \cw{print()} will never be called.
1289 \S{backend-can-print-in-colour} \c{can_print_in_colour}
1291 \c int can_print_in_colour;
1293 This flag is set to \cw{TRUE} if the puzzle is capable of printing
1294 itself differently when colour is available. For example, Map can
1295 actually print coloured regions in different \e{colours} rather than
1296 resorting to cross-hatching.
1298 If the \c{can_print} flag is \cw{FALSE}, then this flag will be
1301 \S{backend-print-size} \cw{print_size()}
1303 \c void (*print_size)(game_params *params, float *x, float *y);
1305 This function is passed a \c{game_params} structure and a tile size.
1306 It returns, in \c{*x} and \c{*y}, the preferred size in
1307 \e{millimetres} of that puzzle if it were to be printed out on paper.
1309 If the \c{can_print} flag is \cw{FALSE}, this function will never be
1312 \S{backend-print} \cw{print()}
1314 \c void (*print)(drawing *dr, game_state *state, int tilesize);
1316 This function is called when a puzzle is to be printed out on paper.
1317 It should use the drawing API functions (see \k{drawing}) to print
1320 This function is separate from \cw{redraw()} because it is often
1323 \b The printing function may not depend on pixel accuracy, since
1324 printer resolution is variable. Draw as if your canvas had infinite
1327 \b The printing function sometimes needs to display things in a
1328 completely different style. Net, for example, is very different as
1329 an on-screen puzzle and as a printed one.
1331 \b The printing function is often much simpler since it has no need
1332 to deal with repeated partial redraws.
1334 However, there's no reason the printing and redraw functions can't
1335 share some code if they want to.
1337 When this function (or any subfunction) calls the drawing API, the
1338 colour indices it passes should be colours which have been allocated
1339 by the \cw{print_*_colour()} functions within this execution of
1340 \cw{print()}. This is very different from the fixed small number of
1341 colours used in \cw{redraw()}, because printers do not have a
1342 limitation on the total number of colours that may be used. Some
1343 puzzles' printing functions might wish to allocate only one \q{ink}
1344 colour and use it for all drawing; others might wish to allocate
1345 \e{more} colours than are used on screen.
1347 One possible colour policy worth mentioning specifically is that a
1348 puzzle's printing function might want to allocate the \e{same}
1349 colour indices as are used by the redraw function, so that code
1350 shared between drawing and printing does not have to keep switching
1351 its colour indices. In order to do this, the simplest thing is to
1352 make use of the fact that colour indices returned from
1353 \cw{print_*_colour()} are guaranteed to be in increasing order from
1354 zero. So if you have declared an \c{enum} defining three colours
1355 \cw{COL_BACKGROUND}, \cw{COL_THIS} and \cw{COL_THAT}, you might then
1359 \c c = print_mono_colour(dr, 1); assert(c == COL_BACKGROUND);
1360 \c c = print_mono_colour(dr, 0); assert(c == COL_THIS);
1361 \c c = print_mono_colour(dr, 0); assert(c == COL_THAT);
1363 If the \c{can_print} flag is \cw{FALSE}, this function will never be
1366 \H{backend-misc} Miscellaneous
1368 \S{backend-can-format-as-text-ever} \c{can_format_as_text_ever}
1370 \c int can_format_as_text_ever;
1372 This boolean field is \cw{TRUE} if the game supports formatting a
1373 game state as ASCII text (typically ASCII art) for copying to the
1374 clipboard and pasting into other applications. If it is \cw{FALSE},
1375 front ends will not offer the \q{Copy} command at all.
1377 If this field is \cw{TRUE}, the game does not necessarily have to
1378 support text formatting for \e{all} games: e.g. a game which can be
1379 played on a square grid or a triangular one might only support copy
1380 and paste for the former, because triangular grids in ASCII art are
1383 If this field is \cw{FALSE}, the functions
1384 \cw{can_format_as_text_now()} (\k{backend-can-format-as-text-now})
1385 and \cw{text_format()} (\k{backend-text-format}) are never called.
1387 \S{backend-can-format-as-text-now} \c{can_format_as_text_now()}
1389 \c int (*can_format_as_text_now)(game_params *params);
1391 This function is passed a \c{game_params} and returns a boolean,
1392 which is \cw{TRUE} if the game can support ASCII text output for
1393 this particular game type. If it returns \cw{FALSE}, front ends will
1394 grey out or otherwise disable the \q{Copy} command.
1396 Games may enable and disable the copy-and-paste function for
1397 different game \e{parameters}, but are currently constrained to
1398 return the same answer from this function for all game \e{states}
1399 sharing the same parameters. In other words, the \q{Copy} function
1400 may enable or disable itself when the player changes game preset,
1401 but will never change during play of a single game or when another
1402 game of exactly the same type is generated.
1404 This function should not take into account aspects of the game
1405 parameters which are not encoded by \cw{encode_params()}
1406 (\k{backend-encode-params}) when the \c{full} parameter is set to
1407 \cw{FALSE}. Such parameters will not necessarily match up between a
1408 call to this function and a subsequent call to \cw{text_format()}
1409 itself. (For instance, game \e{difficulty} should not affect whether
1410 the game can be copied to the clipboard. Only the actual visible
1411 \e{shape} of the game can affect that.)
1413 \S{backend-text-format} \cw{text_format()}
1415 \c char *(*text_format)(game_state *state);
1417 This function is passed a \c{game_state}, and returns a newly
1418 allocated C string containing an ASCII representation of that game
1419 state. It is used to implement the \q{Copy} operation in many front
1422 This function will only ever be called if the back end field
1423 \c{can_format_as_text_ever} (\k{backend-can-format-as-text-ever}) is
1424 \cw{TRUE} \e{and} the function \cw{can_format_as_text_now()}
1425 (\k{backend-can-format-as-text-now}) has returned \cw{TRUE} for the
1426 currently selected game parameters.
1428 The returned string may contain line endings (and will probably want
1429 to), using the normal C internal \cq{\\n} convention. For
1430 consistency between puzzles, all multi-line textual puzzle
1431 representations should \e{end} with a newline as well as containing
1432 them internally. (There are currently no puzzles which have a
1433 one-line ASCII representation, so there's no precedent yet for
1434 whether that should come with a newline or not.)
1436 \S{backend-wants-statusbar} \cw{wants_statusbar()}
1438 \c int wants_statusbar;
1440 This boolean field is set to \cw{TRUE} if the puzzle has a use for a
1441 textual status line (to display score, completion status, currently
1444 \S{backend-is-timed} \c{is_timed}
1448 This boolean field is \cw{TRUE} if the puzzle is time-critical. If
1449 so, the mid-end will maintain a game timer while the user plays.
1451 If this field is \cw{FALSE}, then \cw{timing_state()} will never be
1452 called and need not do anything.
1454 \S{backend-timing-state} \cw{timing_state()}
1456 \c int (*timing_state)(game_state *state, game_ui *ui);
1458 This function is passed the current \c{game_state} and the local
1459 \c{game_ui}; it returns \cw{TRUE} if the game timer should currently
1462 A typical use for the \c{game_ui} in this function is to note when
1463 the game was first completed (by setting a flag in
1464 \cw{changed_state()} \dash see \k{backend-changed-state}), and
1465 freeze the timer thereafter so that the user can undo back through
1466 their solution process without altering their time.
1468 \S{backend-flags} \c{flags}
1472 This field contains miscellaneous per-backend flags. It consists of
1473 the bitwise OR of some combination of the following:
1475 \dt \cw{BUTTON_BEATS(x,y)}
1477 \dd Given any \cw{x} and \cw{y} from the set \{\cw{LEFT_BUTTON},
1478 \cw{MIDDLE_BUTTON}, \cw{RIGHT_BUTTON}\}, this macro evaluates to a
1479 bit flag which indicates that when buttons \cw{x} and \cw{y} are
1480 both pressed simultaneously, the mid-end should consider \cw{x} to
1481 have priority. (In the absence of any such flags, the mid-end will
1482 always consider the most recently pressed button to have priority.)
1484 \dt \cw{SOLVE_ANIMATES}
1486 \dd This flag indicates that moves generated by \cw{solve()}
1487 (\k{backend-solve}) are candidates for animation just like any other
1488 move. For most games, solve moves should not be animated, so the
1489 mid-end doesn't even bother calling \cw{anim_length()}
1490 (\k{backend-anim-length}), thus saving some special-case code in
1491 each game. On the rare occasion that animated solve moves are
1492 actually required, you can set this flag.
1494 \dt \cw{REQUIRE_RBUTTON}
1496 \dd This flag indicates that the puzzle cannot be usefully played
1497 without the use of mouse buttons other than the left one. On some
1498 PDA platforms, this flag is used by the front end to enable
1499 right-button emulation through an appropriate gesture. Note that a
1500 puzzle is not required to set this just because it \e{uses} the
1501 right button, but only if its use of the right button is critical to
1502 playing the game. (Slant, for example, uses the right button to
1503 cycle through the three square states in the opposite order from the
1504 left button, and hence can manage fine without it.)
1506 \dt \cw{REQUIRE_NUMPAD}
1508 \dd This flag indicates that the puzzle cannot be usefully played
1509 without the use of number-key input. On some PDA platforms it causes
1510 an emulated number pad to appear on the screen. Similarly to
1511 \cw{REQUIRE_RBUTTON}, a puzzle need not specify this simply if its
1512 use of the number keys is not critical.
1514 \H{backend-initiative} Things a back end may do on its own initiative
1516 This section describes a couple of things that a back end may choose
1517 to do by calling functions elsewhere in the program, which would not
1518 otherwise be obvious.
1520 \S{backend-newrs} Create a random state
1522 If a back end needs random numbers at some point during normal play,
1523 it can create a fresh \c{random_state} by first calling
1524 \c{get_random_seed} (\k{frontend-get-random-seed}) and then passing
1525 the returned seed data to \cw{random_new()}.
1527 This is likely not to be what you want. If a puzzle needs randomness
1528 in the middle of play, it's likely to be more sensible to store some
1529 sort of random state within the \c{game_state}, so that the random
1530 numbers are tied to the particular game state and hence the player
1531 can't simply keep undoing their move until they get numbers they
1534 This facility is currently used only in Net, to implement the
1535 \q{jumble} command, which sets every unlocked tile to a new random
1536 orientation. This randomness \e{is} a reasonable use of the feature,
1537 because it's non-adversarial \dash there's no advantage to the user
1538 in getting different random numbers.
1540 \S{backend-supersede} Supersede its own game description
1542 In response to a move, a back end is (reluctantly) permitted to call
1543 \cw{midend_supersede_game_desc()}:
1545 \c void midend_supersede_game_desc(midend *me,
1546 \c char *desc, char *privdesc);
1548 When the user selects \q{New Game}, the mid-end calls
1549 \cw{new_desc()} (\k{backend-new-desc}) to get a new game
1550 description, and (as well as using that to generate an initial game
1551 state) stores it for the save file and for telling to the user. The
1552 function above overwrites that game description, and also splits it
1553 in two. \c{desc} becomes the new game description which is provided
1554 to the user on request, and is also the one used to construct a new
1555 initial game state if the user selects \q{Restart}. \c{privdesc} is
1556 a \q{private} game description, used to reconstruct the game's
1557 initial state when reloading.
1559 The distinction between the two, as well as the need for this
1560 function at all, comes from Mines. Mines begins with a blank grid
1561 and no idea of where the mines actually are; \cw{new_desc()} does
1562 almost no work in interactive mode, and simply returns a string
1563 encoding the \c{random_state}. When the user first clicks to open a
1564 tile, \e{then} Mines generates the mine positions, in such a way
1565 that the game is soluble from that starting point. Then it uses this
1566 function to supersede the random-state game description with a
1567 proper one. But it needs two: one containing the initial click
1568 location (because that's what you want to happen if you restart the
1569 game, and also what you want to send to a friend so that they play
1570 \e{the same game} as you), and one without the initial click
1571 location (because when you save and reload the game, you expect to
1572 see the same blank initial state as you had before saving).
1574 I should stress again that this function is a horrid hack. Nobody
1575 should use it if they're not Mines; if you think you need to use it,
1576 think again repeatedly in the hope of finding a better way to do
1577 whatever it was you needed to do.
1579 \C{drawing} The drawing API
1581 The back end function \cw{redraw()} (\k{backend-redraw}) is required
1582 to draw the puzzle's graphics on the window's drawing area, or on
1583 paper if the puzzle is printable. To do this portably, it is
1584 provided with a drawing API allowing it to talk directly to the
1585 front end. In this chapter I document that API, both for the benefit
1586 of back end authors trying to use it and for front end authors
1587 trying to implement it.
1589 The drawing API as seen by the back end is a collection of global
1590 functions, each of which takes a pointer to a \c{drawing} structure
1591 (a \q{drawing object}). These objects are supplied as parameters to
1592 the back end's \cw{redraw()} and \cw{print()} functions.
1594 In fact these global functions are not implemented directly by the
1595 front end; instead, they are implemented centrally in \c{drawing.c}
1596 and form a small piece of middleware. The drawing API as supplied by
1597 the front end is a structure containing a set of function pointers,
1598 plus a \cq{void *} handle which is passed to each of those
1599 functions. This enables a single front end to switch between
1600 multiple implementations of the drawing API if necessary. For
1601 example, the Windows API supplies a printing mechanism integrated
1602 into the same GDI which deals with drawing in windows, and therefore
1603 the same API implementation can handle both drawing and printing;
1604 but on Unix, the most common way for applications to print is by
1605 producing PostScript output directly, and although it would be
1606 \e{possible} to write a single (say) \cw{draw_rect()} function which
1607 checked a global flag to decide whether to do GTK drawing operations
1608 or output PostScript to a file, it's much nicer to have two separate
1609 functions and switch between them as appropriate.
1611 When drawing, the puzzle window is indexed by pixel coordinates,
1612 with the top left pixel defined as \cw{(0,0)} and the bottom right
1613 pixel \cw{(w-1,h-1)}, where \c{w} and \c{h} are the width and height
1614 values returned by the back end function \cw{compute_size()}
1615 (\k{backend-compute-size}).
1617 When printing, the puzzle's print area is indexed in exactly the
1618 same way (with an arbitrary tile size provided by the printing
1619 module \c{printing.c}), to facilitate sharing of code between the
1620 drawing and printing routines. However, when printing, puzzles may
1621 no longer assume that the coordinate unit has any relationship to a
1622 pixel; the printer's actual resolution might very well not even be
1623 known at print time, so the coordinate unit might be smaller or
1624 larger than a pixel. Puzzles' print functions should restrict
1625 themselves to drawing geometric shapes rather than fiddly pixel
1628 \e{Puzzles' redraw functions may assume that the surface they draw
1629 on is persistent}. It is the responsibility of every front end to
1630 preserve the puzzle's window contents in the face of GUI window
1631 expose issues and similar. It is not permissible to request that the
1632 back end redraw any part of a window that it has already drawn,
1633 unless something has actually changed as a result of making moves in
1636 Most front ends accomplish this by having the drawing routines draw
1637 on a stored bitmap rather than directly on the window, and copying
1638 the bitmap to the window every time a part of the window needs to be
1639 redrawn. Therefore, it is vitally important that whenever the back
1640 end does any drawing it informs the front end of which parts of the
1641 window it has accessed, and hence which parts need repainting. This
1642 is done by calling \cw{draw_update()} (\k{drawing-draw-update}).
1644 In the following sections I first discuss the drawing API as seen by
1645 the back end, and then the \e{almost} identical function-pointer
1646 form seen by the front end.
1648 \H{drawing-backend} Drawing API as seen by the back end
1650 This section documents the back-end drawing API, in the form of
1651 functions which take a \c{drawing} object as an argument.
1653 \S{drawing-draw-rect} \cw{draw_rect()}
1655 \c void draw_rect(drawing *dr, int x, int y, int w, int h,
1658 Draws a filled rectangle in the puzzle window.
1660 \c{x} and \c{y} give the coordinates of the top left pixel of the
1661 rectangle. \c{w} and \c{h} give its width and height. Thus, the
1662 horizontal extent of the rectangle runs from \c{x} to \c{x+w-1}
1663 inclusive, and the vertical extent from \c{y} to \c{y+h-1}
1666 \c{colour} is an integer index into the colours array returned by
1667 the back end function \cw{colours()} (\k{backend-colours}).
1669 There is no separate pixel-plotting function. If you want to plot a
1670 single pixel, the approved method is to use \cw{draw_rect()} with
1671 width and height set to 1.
1673 Unlike many of the other drawing functions, this function is
1674 guaranteed to be pixel-perfect: the rectangle will be sharply
1675 defined and not anti-aliased or anything like that.
1677 This function may be used for both drawing and printing.
1679 \S{drawing-draw-rect-outline} \cw{draw_rect_outline()}
1681 \c void draw_rect_outline(drawing *dr, int x, int y, int w, int h,
1684 Draws an outline rectangle in the puzzle window.
1686 \c{x} and \c{y} give the coordinates of the top left pixel of the
1687 rectangle. \c{w} and \c{h} give its width and height. Thus, the
1688 horizontal extent of the rectangle runs from \c{x} to \c{x+w-1}
1689 inclusive, and the vertical extent from \c{y} to \c{y+h-1}
1692 \c{colour} is an integer index into the colours array returned by
1693 the back end function \cw{colours()} (\k{backend-colours}).
1695 From a back end perspective, this function may be considered to be
1696 part of the drawing API. However, front ends are not required to
1697 implement it, since it is actually implemented centrally (in
1698 \cw{misc.c}) as a wrapper on \cw{draw_polygon()}.
1700 This function may be used for both drawing and printing.
1702 \S{drawing-draw-line} \cw{draw_line()}
1704 \c void draw_line(drawing *dr, int x1, int y1, int x2, int y2,
1707 Draws a straight line in the puzzle window.
1709 \c{x1} and \c{y1} give the coordinates of one end of the line.
1710 \c{x2} and \c{y2} give the coordinates of the other end. The line
1711 drawn includes both those points.
1713 \c{colour} is an integer index into the colours array returned by
1714 the back end function \cw{colours()} (\k{backend-colours}).
1716 Some platforms may perform anti-aliasing on this function.
1717 Therefore, do not assume that you can erase a line by drawing the
1718 same line over it in the background colour; anti-aliasing might
1719 lead to perceptible ghost artefacts around the vanished line.
1721 This function may be used for both drawing and printing.
1723 \S{drawing-draw-polygon} \cw{draw_polygon()}
1725 \c void draw_polygon(drawing *dr, int *coords, int npoints,
1726 \c int fillcolour, int outlinecolour);
1728 Draws an outlined or filled polygon in the puzzle window.
1730 \c{coords} is an array of \cw{(2*npoints)} integers, containing the
1731 \c{x} and \c{y} coordinates of \c{npoints} vertices.
1733 \c{fillcolour} and \c{outlinecolour} are integer indices into the
1734 colours array returned by the back end function \cw{colours()}
1735 (\k{backend-colours}). \c{fillcolour} may also be \cw{-1} to
1736 indicate that the polygon should be outlined only.
1738 The polygon defined by the specified list of vertices is first
1739 filled in \c{fillcolour}, if specified, and then outlined in
1742 \c{outlinecolour} may \e{not} be \cw{-1}; it must be a valid colour
1743 (and front ends are permitted to enforce this by assertion). This is
1744 because different platforms disagree on whether a filled polygon
1745 should include its boundary line or not, so drawing \e{only} a
1746 filled polygon would have non-portable effects. If you want your
1747 filled polygon not to have a visible outline, you must set
1748 \c{outlinecolour} to the same as \c{fillcolour}.
1750 Some platforms may perform anti-aliasing on this function.
1751 Therefore, do not assume that you can erase a polygon by drawing the
1752 same polygon over it in the background colour. Also, be prepared for
1753 the polygon to extend a pixel beyond its obvious bounding box as a
1754 result of this; if you really need it not to do this to avoid
1755 interfering with other delicate graphics, you should probably use
1756 \cw{clip()} (\k{drawing-clip}).
1758 This function may be used for both drawing and printing.
1760 \S{drawing-draw-circle} \cw{draw_circle()}
1762 \c void draw_circle(drawing *dr, int cx, int cy, int radius,
1763 \c int fillcolour, int outlinecolour);
1765 Draws an outlined or filled circle in the puzzle window.
1767 \c{cx} and \c{cy} give the coordinates of the centre of the circle.
1768 \c{radius} gives its radius. The total horizontal pixel extent of
1769 the circle is from \c{cx-radius+1} to \c{cx+radius-1} inclusive, and
1770 the vertical extent similarly around \c{cy}.
1772 \c{fillcolour} and \c{outlinecolour} are integer indices into the
1773 colours array returned by the back end function \cw{colours()}
1774 (\k{backend-colours}). \c{fillcolour} may also be \cw{-1} to
1775 indicate that the circle should be outlined only.
1777 The circle is first filled in \c{fillcolour}, if specified, and then
1778 outlined in \c{outlinecolour}.
1780 \c{outlinecolour} may \e{not} be \cw{-1}; it must be a valid colour
1781 (and front ends are permitted to enforce this by assertion). This is
1782 because different platforms disagree on whether a filled circle
1783 should include its boundary line or not, so drawing \e{only} a
1784 filled circle would have non-portable effects. If you want your
1785 filled circle not to have a visible outline, you must set
1786 \c{outlinecolour} to the same as \c{fillcolour}.
1788 Some platforms may perform anti-aliasing on this function.
1789 Therefore, do not assume that you can erase a circle by drawing the
1790 same circle over it in the background colour. Also, be prepared for
1791 the circle to extend a pixel beyond its obvious bounding box as a
1792 result of this; if you really need it not to do this to avoid
1793 interfering with other delicate graphics, you should probably use
1794 \cw{clip()} (\k{drawing-clip}).
1796 This function may be used for both drawing and printing.
1798 \S{drawing-draw-text} \cw{draw_text()}
1800 \c void draw_text(drawing *dr, int x, int y, int fonttype,
1801 \c int fontsize, int align, int colour, char *text);
1803 Draws text in the puzzle window.
1805 \c{x} and \c{y} give the coordinates of a point. The relation of
1806 this point to the location of the text is specified by \c{align},
1807 which is a bitwise OR of horizontal and vertical alignment flags:
1809 \dt \cw{ALIGN_VNORMAL}
1811 \dd Indicates that \c{y} is aligned with the baseline of the text.
1813 \dt \cw{ALIGN_VCENTRE}
1815 \dd Indicates that \c{y} is aligned with the vertical centre of the
1816 text. (In fact, it's aligned with the vertical centre of normal
1817 \e{capitalised} text: displaying two pieces of text with
1818 \cw{ALIGN_VCENTRE} at the same \cw{y}-coordinate will cause their
1819 baselines to be aligned with one another, even if one is an ascender
1820 and the other a descender.)
1822 \dt \cw{ALIGN_HLEFT}
1824 \dd Indicates that \c{x} is aligned with the left-hand end of the
1827 \dt \cw{ALIGN_HCENTRE}
1829 \dd Indicates that \c{x} is aligned with the horizontal centre of
1832 \dt \cw{ALIGN_HRIGHT}
1834 \dd Indicates that \c{x} is aligned with the right-hand end of the
1837 \c{fonttype} is either \cw{FONT_FIXED} or \cw{FONT_VARIABLE}, for a
1838 monospaced or proportional font respectively. (No more detail than
1839 that may be specified; it would only lead to portability issues
1840 between different platforms.)
1842 \c{fontsize} is the desired size, in pixels, of the text. This size
1843 corresponds to the overall point size of the text, not to any
1844 internal dimension such as the cap-height.
1846 \c{colour} is an integer index into the colours array returned by
1847 the back end function \cw{colours()} (\k{backend-colours}).
1849 This function may be used for both drawing and printing.
1851 \S{drawing-clip} \cw{clip()}
1853 \c void clip(drawing *dr, int x, int y, int w, int h);
1855 Establishes a clipping rectangle in the puzzle window.
1857 \c{x} and \c{y} give the coordinates of the top left pixel of the
1858 clipping rectangle. \c{w} and \c{h} give its width and height. Thus,
1859 the horizontal extent of the rectangle runs from \c{x} to \c{x+w-1}
1860 inclusive, and the vertical extent from \c{y} to \c{y+h-1}
1861 inclusive. (These are exactly the same semantics as
1864 After this call, no drawing operation will affect anything outside
1865 the specified rectangle. The effect can be reversed by calling
1866 \cw{unclip()} (\k{drawing-unclip}).
1868 Back ends should not assume that a clipping rectangle will be
1869 automatically cleared up by the front end if it's left lying around;
1870 that might work on current front ends, but shouldn't be relied upon.
1871 Always explicitly call \cw{unclip()}.
1873 This function may be used for both drawing and printing.
1875 \S{drawing-unclip} \cw{unclip()}
1877 \c void unclip(drawing *dr);
1879 Reverts the effect of a previous call to \cw{clip()}. After this
1880 call, all drawing operations will be able to affect the entire
1881 puzzle window again.
1883 This function may be used for both drawing and printing.
1885 \S{drawing-draw-update} \cw{draw_update()}
1887 \c void draw_update(drawing *dr, int x, int y, int w, int h);
1889 Informs the front end that a rectangular portion of the puzzle
1890 window has been drawn on and needs to be updated.
1892 \c{x} and \c{y} give the coordinates of the top left pixel of the
1893 update rectangle. \c{w} and \c{h} give its width and height. Thus,
1894 the horizontal extent of the rectangle runs from \c{x} to \c{x+w-1}
1895 inclusive, and the vertical extent from \c{y} to \c{y+h-1}
1896 inclusive. (These are exactly the same semantics as
1899 The back end redraw function \e{must} call this function to report
1900 any changes it has made to the window. Otherwise, those changes may
1901 not become immediately visible, and may then appear at an
1902 unpredictable subsequent time such as the next time the window is
1903 covered and re-exposed.
1905 This function is only important when drawing. It may be called when
1906 printing as well, but doing so is not compulsory, and has no effect.
1907 (So if you have a shared piece of code between the drawing and
1908 printing routines, that code may safely call \cw{draw_update()}.)
1910 \S{drawing-status-bar} \cw{status_bar()}
1912 \c void status_bar(drawing *dr, char *text);
1914 Sets the text in the game's status bar to \c{text}. The text is copied
1915 from the supplied buffer, so the caller is free to deallocate or
1916 modify the buffer after use.
1918 (This function is not exactly a \e{drawing} function, but it shares
1919 with the drawing API the property that it may only be called from
1920 within the back end redraw function, so this is as good a place as
1921 any to document it.)
1923 The supplied text is filtered through the mid-end for optional
1924 rewriting before being passed on to the front end; the mid-end will
1925 prepend the current game time if the game is timed (and may in
1926 future perform other rewriting if it seems like a good idea).
1928 This function is for drawing only; it must never be called during
1931 \S{drawing-blitter} Blitter functions
1933 This section describes a group of related functions which save and
1934 restore a section of the puzzle window. This is most commonly used
1935 to implement user interfaces involving dragging a puzzle element
1936 around the window: at the end of each call to \cw{redraw()}, if an
1937 object is currently being dragged, the back end saves the window
1938 contents under that location and then draws the dragged object, and
1939 at the start of the next \cw{redraw()} the first thing it does is to
1940 restore the background.
1942 The front end defines an opaque type called a \c{blitter}, which is
1943 capable of storing a rectangular area of a specified size.
1945 Blitter functions are for drawing only; they must never be called
1948 \S2{drawing-blitter-new} \cw{blitter_new()}
1950 \c blitter *blitter_new(drawing *dr, int w, int h);
1952 Creates a new blitter object which stores a rectangle of size \c{w}
1953 by \c{h} pixels. Returns a pointer to the blitter object.
1955 Blitter objects are best stored in the \c{game_drawstate}. A good
1956 time to create them is in the \cw{set_size()} function
1957 (\k{backend-set-size}), since it is at this point that you first
1958 know how big a rectangle they will need to save.
1960 \S2{drawing-blitter-free} \cw{blitter_free()}
1962 \c void blitter_free(drawing *dr, blitter *bl);
1964 Disposes of a blitter object. Best called in \cw{free_drawstate()}.
1965 (However, check that the blitter object is not \cw{NULL} before
1966 attempting to free it; it is possible that a draw state might be
1967 created and freed without ever having \cw{set_size()} called on it
1970 \S2{drawing-blitter-save} \cw{blitter_save()}
1972 \c void blitter_save(drawing *dr, blitter *bl, int x, int y);
1974 This is a true drawing API function, in that it may only be called
1975 from within the game redraw routine. It saves a rectangular portion
1976 of the puzzle window into the specified blitter object.
1978 \c{x} and \c{y} give the coordinates of the top left corner of the
1979 saved rectangle. The rectangle's width and height are the ones
1980 specified when the blitter object was created.
1982 This function is required to cope and do the right thing if \c{x}
1983 and \c{y} are out of range. (The right thing probably means saving
1984 whatever part of the blitter rectangle overlaps with the visible
1985 area of the puzzle window.)
1987 \S2{drawing-blitter-load} \cw{blitter_load()}
1989 \c void blitter_load(drawing *dr, blitter *bl, int x, int y);
1991 This is a true drawing API function, in that it may only be called
1992 from within the game redraw routine. It restores a rectangular
1993 portion of the puzzle window from the specified blitter object.
1995 \c{x} and \c{y} give the coordinates of the top left corner of the
1996 rectangle to be restored. The rectangle's width and height are the
1997 ones specified when the blitter object was created.
1999 Alternatively, you can specify both \c{x} and \c{y} as the special
2000 value \cw{BLITTER_FROMSAVED}, in which case the rectangle will be
2001 restored to exactly where it was saved from. (This is probably what
2002 you want to do almost all the time, if you're using blitters to
2003 implement draggable puzzle elements.)
2005 This function is required to cope and do the right thing if \c{x}
2006 and \c{y} (or the equivalent ones saved in the blitter) are out of
2007 range. (The right thing probably means restoring whatever part of
2008 the blitter rectangle overlaps with the visible area of the puzzle
2011 If this function is called on a blitter which had previously been
2012 saved from a partially out-of-range rectangle, then the parts of the
2013 saved bitmap which were not visible at save time are undefined. If
2014 the blitter is restored to a different position so as to make those
2015 parts visible, the effect on the drawing area is undefined.
2017 \S{print-mono-colour} \cw{print_mono_colour()}
2019 \c int print_mono_colour(drawing *dr, int grey);
2021 This function allocates a colour index for a simple monochrome
2022 colour during printing.
2024 \c{grey} must be 0 or 1. If \c{grey} is 0, the colour returned is
2025 black; if \c{grey} is 1, the colour is white.
2027 \S{print-grey-colour} \cw{print_grey_colour()}
2029 \c int print_grey_colour(drawing *dr, float grey);
2031 This function allocates a colour index for a grey-scale colour
2034 \c{grey} may be any number between 0 (black) and 1 (white); for
2035 example, 0.5 indicates a medium grey.
2037 The chosen colour will be rendered to the limits of the printer's
2038 halftoning capability.
2040 \S{print-hatched-colour} \cw{print_hatched_colour()}
2042 \c int print_hatched_colour(drawing *dr, int hatch);
2044 This function allocates a colour index which does not represent a
2045 literal \e{colour}. Instead, regions shaded in this colour will be
2046 hatched with parallel lines. The \c{hatch} parameter defines what
2047 type of hatching should be used in place of this colour:
2049 \dt \cw{HATCH_SLASH}
2051 \dd This colour will be hatched by lines slanting to the right at 45
2054 \dt \cw{HATCH_BACKSLASH}
2056 \dd This colour will be hatched by lines slanting to the left at 45
2059 \dt \cw{HATCH_HORIZ}
2061 \dd This colour will be hatched by horizontal lines.
2065 \dd This colour will be hatched by vertical lines.
2069 \dd This colour will be hatched by criss-crossing horizontal and
2074 \dd This colour will be hatched by criss-crossing diagonal lines.
2076 Colours defined to use hatching may not be used for drawing lines or
2077 text; they may only be used for filling areas. That is, they may be
2078 used as the \c{fillcolour} parameter to \cw{draw_circle()} and
2079 \cw{draw_polygon()}, and as the colour parameter to
2080 \cw{draw_rect()}, but may not be used as the \c{outlinecolour}
2081 parameter to \cw{draw_circle()} or \cw{draw_polygon()}, or with
2082 \cw{draw_line()} or \cw{draw_text()}.
2084 \S{print-rgb-mono-colour} \cw{print_rgb_mono_colour()}
2086 \c int print_rgb_mono_colour(drawing *dr, float r, float g,
2087 \c float b, float grey);
2089 This function allocates a colour index for a fully specified RGB
2090 colour during printing.
2092 \c{r}, \c{g} and \c{b} may each be anywhere in the range from 0 to 1.
2094 If printing in black and white only, these values will be ignored,
2095 and either pure black or pure white will be used instead, according
2096 to the \q{grey} parameter. (The fallback colour is the same as the
2097 one which would be allocated by \cw{print_mono_colour(grey)}.)
2099 \S{print-rgb-grey-colour} \cw{print_rgb_grey_colour()}
2101 \c int print_rgb_grey_colour(drawing *dr, float r, float g,
2102 \c float b, float grey);
2104 This function allocates a colour index for a fully specified RGB
2105 colour during printing.
2107 \c{r}, \c{g} and \c{b} may each be anywhere in the range from 0 to 1.
2109 If printing in black and white only, these values will be ignored,
2110 and a shade of grey given by the \c{grey} parameter will be used
2111 instead. (The fallback colour is the same as the one which would be
2112 allocated by \cw{print_grey_colour(grey)}.)
2114 \S{print-rgb-hatched-colour} \cw{print_rgb_hatched_colour()}
2116 \c int print_rgb_hatched_colour(drawing *dr, float r, float g,
2117 \c float b, float hatched);
2119 This function allocates a colour index for a fully specified RGB
2120 colour during printing.
2122 \c{r}, \c{g} and \c{b} may each be anywhere in the range from 0 to 1.
2124 If printing in black and white only, these values will be ignored,
2125 and a form of cross-hatching given by the \c{hatch} parameter will
2126 be used instead; see \k{print-hatched-colour} for the possible
2127 values of this parameter. (The fallback colour is the same as the
2128 one which would be allocated by \cw{print_hatched_colour(hatch)}.)
2130 \S{print-line-width} \cw{print_line_width()}
2132 \c void print_line_width(drawing *dr, int width);
2134 This function is called to set the thickness of lines drawn during
2135 printing. It is meaningless in drawing: all lines drawn by
2136 \cw{draw_line()}, \cw{draw_circle} and \cw{draw_polygon()} are one
2137 pixel in thickness. However, in printing there is no clear
2138 definition of a pixel and so line widths must be explicitly
2141 The line width is specified in the usual coordinate system. Note,
2142 however, that it is a hint only: the central printing system may
2143 choose to vary line thicknesses at user request or due to printer
2146 \S{print-line-dotted} \cw{print_line_dotted()}
2148 \c void print_line_dotted(drawing *dr, int dotted);
2150 This function is called to toggle the drawing of dotted lines during
2151 printing. It is not supported during drawing.
2153 The parameter \cq{dotted} is a boolean; \cw{TRUE} means that future
2154 lines drawn by \cw{draw_line()}, \cw{draw_circle} and
2155 \cw{draw_polygon()} will be dotted, and \cw{FALSE} means that they
2158 Some front ends may impose restrictions on the width of dotted
2159 lines. Asking for a dotted line via this front end will override any
2160 line width request if the front end requires it.
2162 \H{drawing-frontend} The drawing API as implemented by the front end
2164 This section describes the drawing API in the function-pointer form
2165 in which it is implemented by a front end.
2167 (It isn't only platform-specific front ends which implement this
2168 API; the platform-independent module \c{ps.c} also provides an
2169 implementation of it which outputs PostScript. Thus, any platform
2170 which wants to do PS printing can do so with minimum fuss.)
2172 The following entries all describe function pointer fields in a
2173 structure called \c{drawing_api}. Each of the functions takes a
2174 \cq{void *} context pointer, which it should internally cast back to
2175 a more useful type. Thus, a drawing \e{object} (\c{drawing *)}
2176 suitable for passing to the back end redraw or printing functions
2177 is constructed by passing a \c{drawing_api} and a \cq{void *} to the
2178 function \cw{drawing_new()} (see \k{drawing-new}).
2180 \S{drawingapi-draw-text} \cw{draw_text()}
2182 \c void (*draw_text)(void *handle, int x, int y, int fonttype,
2183 \c int fontsize, int align, int colour, char *text);
2185 This function behaves exactly like the back end \cw{draw_text()}
2186 function; see \k{drawing-draw-text}.
2188 \S{drawingapi-draw-rect} \cw{draw_rect()}
2190 \c void (*draw_rect)(void *handle, int x, int y, int w, int h,
2193 This function behaves exactly like the back end \cw{draw_rect()}
2194 function; see \k{drawing-draw-rect}.
2196 \S{drawingapi-draw-line} \cw{draw_line()}
2198 \c void (*draw_line)(void *handle, int x1, int y1, int x2, int y2,
2201 This function behaves exactly like the back end \cw{draw_line()}
2202 function; see \k{drawing-draw-line}.
2204 \S{drawingapi-draw-polygon} \cw{draw_polygon()}
2206 \c void (*draw_polygon)(void *handle, int *coords, int npoints,
2207 \c int fillcolour, int outlinecolour);
2209 This function behaves exactly like the back end \cw{draw_polygon()}
2210 function; see \k{drawing-draw-polygon}.
2212 \S{drawingapi-draw-circle} \cw{draw_circle()}
2214 \c void (*draw_circle)(void *handle, int cx, int cy, int radius,
2215 \c int fillcolour, int outlinecolour);
2217 This function behaves exactly like the back end \cw{draw_circle()}
2218 function; see \k{drawing-draw-circle}.
2220 \S{drawingapi-draw-update} \cw{draw_update()}
2222 \c void (*draw_update)(void *handle, int x, int y, int w, int h);
2224 This function behaves exactly like the back end \cw{draw_update()}
2225 function; see \k{drawing-draw-update}.
2227 An implementation of this API which only supports printing is
2228 permitted to define this function pointer to be \cw{NULL} rather
2229 than bothering to define an empty function. The middleware in
2230 \cw{drawing.c} will notice and avoid calling it.
2232 \S{drawingapi-clip} \cw{clip()}
2234 \c void (*clip)(void *handle, int x, int y, int w, int h);
2236 This function behaves exactly like the back end \cw{clip()}
2237 function; see \k{drawing-clip}.
2239 \S{drawingapi-unclip} \cw{unclip()}
2241 \c void (*unclip)(void *handle);
2243 This function behaves exactly like the back end \cw{unclip()}
2244 function; see \k{drawing-unclip}.
2246 \S{drawingapi-start-draw} \cw{start_draw()}
2248 \c void (*start_draw)(void *handle);
2250 This function is called at the start of drawing. It allows the front
2251 end to initialise any temporary data required to draw with, such as
2254 Implementations of this API which do not provide drawing services
2255 may define this function pointer to be \cw{NULL}; it will never be
2256 called unless drawing is attempted.
2258 \S{drawingapi-end-draw} \cw{end_draw()}
2260 \c void (*end_draw)(void *handle);
2262 This function is called at the end of drawing. It allows the front
2263 end to do cleanup tasks such as deallocating device contexts and
2264 scheduling appropriate GUI redraw events.
2266 Implementations of this API which do not provide drawing services
2267 may define this function pointer to be \cw{NULL}; it will never be
2268 called unless drawing is attempted.
2270 \S{drawingapi-status-bar} \cw{status_bar()}
2272 \c void (*status_bar)(void *handle, char *text);
2274 This function behaves exactly like the back end \cw{status_bar()}
2275 function; see \k{drawing-status-bar}.
2277 Front ends implementing this function need not worry about it being
2278 called repeatedly with the same text; the middleware code in
2279 \cw{status_bar()} will take care of this.
2281 Implementations of this API which do not provide drawing services
2282 may define this function pointer to be \cw{NULL}; it will never be
2283 called unless drawing is attempted.
2285 \S{drawingapi-blitter-new} \cw{blitter_new()}
2287 \c blitter *(*blitter_new)(void *handle, int w, int h);
2289 This function behaves exactly like the back end \cw{blitter_new()}
2290 function; see \k{drawing-blitter-new}.
2292 Implementations of this API which do not provide drawing services
2293 may define this function pointer to be \cw{NULL}; it will never be
2294 called unless drawing is attempted.
2296 \S{drawingapi-blitter-free} \cw{blitter_free()}
2298 \c void (*blitter_free)(void *handle, blitter *bl);
2300 This function behaves exactly like the back end \cw{blitter_free()}
2301 function; see \k{drawing-blitter-free}.
2303 Implementations of this API which do not provide drawing services
2304 may define this function pointer to be \cw{NULL}; it will never be
2305 called unless drawing is attempted.
2307 \S{drawingapi-blitter-save} \cw{blitter_save()}
2309 \c void (*blitter_save)(void *handle, blitter *bl, int x, int y);
2311 This function behaves exactly like the back end \cw{blitter_save()}
2312 function; see \k{drawing-blitter-save}.
2314 Implementations of this API which do not provide drawing services
2315 may define this function pointer to be \cw{NULL}; it will never be
2316 called unless drawing is attempted.
2318 \S{drawingapi-blitter-load} \cw{blitter_load()}
2320 \c void (*blitter_load)(void *handle, blitter *bl, int x, int y);
2322 This function behaves exactly like the back end \cw{blitter_load()}
2323 function; see \k{drawing-blitter-load}.
2325 Implementations of this API which do not provide drawing services
2326 may define this function pointer to be \cw{NULL}; it will never be
2327 called unless drawing is attempted.
2329 \S{drawingapi-begin-doc} \cw{begin_doc()}
2331 \c void (*begin_doc)(void *handle, int pages);
2333 This function is called at the beginning of a printing run. It gives
2334 the front end an opportunity to initialise any required printing
2335 subsystem. It also provides the number of pages in advance.
2337 Implementations of this API which do not provide printing services
2338 may define this function pointer to be \cw{NULL}; it will never be
2339 called unless printing is attempted.
2341 \S{drawingapi-begin-page} \cw{begin_page()}
2343 \c void (*begin_page)(void *handle, int number);
2345 This function is called during printing, at the beginning of each
2346 page. It gives the page number (numbered from 1 rather than 0, so
2347 suitable for use in user-visible contexts).
2349 Implementations of this API which do not provide printing services
2350 may define this function pointer to be \cw{NULL}; it will never be
2351 called unless printing is attempted.
2353 \S{drawingapi-begin-puzzle} \cw{begin_puzzle()}
2355 \c void (*begin_puzzle)(void *handle, float xm, float xc,
2356 \c float ym, float yc, int pw, int ph, float wmm);
2358 This function is called during printing, just before printing a
2359 single puzzle on a page. It specifies the size and location of the
2362 \c{xm} and \c{xc} specify the horizontal position of the puzzle on
2363 the page, as a linear function of the page width. The front end is
2364 expected to multiply the page width by \c{xm}, add \c{xc} (measured
2365 in millimetres), and use the resulting x-coordinate as the left edge
2368 Similarly, \c{ym} and \c{yc} specify the vertical position of the
2369 puzzle as a function of the page height: the page height times
2370 \c{ym}, plus \c{yc} millimetres, equals the desired distance from
2371 the top of the page to the top of the puzzle.
2373 (This unwieldy mechanism is required because not all printing
2374 systems can communicate the page size back to the software. The
2375 PostScript back end, for example, writes out PS which determines the
2376 page size at print time by means of calling \cq{clippath}, and
2377 centres the puzzles within that. Thus, exactly the same PS file
2378 works on A4 or on US Letter paper without needing local
2379 configuration, which simplifies matters.)
2381 \cw{pw} and \cw{ph} give the size of the puzzle in drawing API
2382 coordinates. The printing system will subsequently call the puzzle's
2383 own print function, which will in turn call drawing API functions in
2384 the expectation that an area \cw{pw} by \cw{ph} units is available
2385 to draw the puzzle on.
2387 Finally, \cw{wmm} gives the desired width of the puzzle in
2388 millimetres. (The aspect ratio is expected to be preserved, so if
2389 the desired puzzle height is also needed then it can be computed as
2392 Implementations of this API which do not provide printing services
2393 may define this function pointer to be \cw{NULL}; it will never be
2394 called unless printing is attempted.
2396 \S{drawingapi-end-puzzle} \cw{end_puzzle()}
2398 \c void (*end_puzzle)(void *handle);
2400 This function is called after the printing of a specific puzzle is
2403 Implementations of this API which do not provide printing services
2404 may define this function pointer to be \cw{NULL}; it will never be
2405 called unless printing is attempted.
2407 \S{drawingapi-end-page} \cw{end_page()}
2409 \c void (*end_page)(void *handle, int number);
2411 This function is called after the printing of a page is finished.
2413 Implementations of this API which do not provide printing services
2414 may define this function pointer to be \cw{NULL}; it will never be
2415 called unless printing is attempted.
2417 \S{drawingapi-end-doc} \cw{end_doc()}
2419 \c void (*end_doc)(void *handle);
2421 This function is called after the printing of the entire document is
2422 finished. This is the moment to close files, send things to the
2423 print spooler, or whatever the local convention is.
2425 Implementations of this API which do not provide printing services
2426 may define this function pointer to be \cw{NULL}; it will never be
2427 called unless printing is attempted.
2429 \S{drawingapi-line-width} \cw{line_width()}
2431 \c void (*line_width)(void *handle, float width);
2433 This function is called to set the line thickness, during printing
2434 only. Note that the width is a \cw{float} here, where it was an
2435 \cw{int} as seen by the back end. This is because \cw{drawing.c} may
2436 have scaled it on the way past.
2438 However, the width is still specified in the same coordinate system
2439 as the rest of the drawing.
2441 Implementations of this API which do not provide printing services
2442 may define this function pointer to be \cw{NULL}; it will never be
2443 called unless printing is attempted.
2445 \H{drawingapi-frontend} The drawing API as called by the front end
2447 There are a small number of functions provided in \cw{drawing.c}
2448 which the front end needs to \e{call}, rather than helping to
2449 implement. They are described in this section.
2451 \S{drawing-new} \cw{drawing_new()}
2453 \c drawing *drawing_new(const drawing_api *api, midend *me,
2456 This function creates a drawing object. It is passed a
2457 \c{drawing_api}, which is a structure containing nothing but
2458 function pointers; and also a \cq{void *} handle. The handle is
2459 passed back to each function pointer when it is called.
2461 The \c{midend} parameter is used for rewriting the status bar
2462 contents: \cw{status_bar()} (see \k{drawing-status-bar}) has to call
2463 a function in the mid-end which might rewrite the status bar text.
2464 If the drawing object is to be used only for printing, or if the
2465 game is known not to call \cw{status_bar()}, this parameter may be
2468 \S{drawing-free} \cw{drawing_free()}
2470 \c void drawing_free(drawing *dr);
2472 This function frees a drawing object. Note that the \cq{void *}
2473 handle is not freed; if that needs cleaning up it must be done by
2476 \S{drawing-print-get-colour} \cw{print_get_colour()}
2478 \c void print_get_colour(drawing *dr, int colour, int printincolour,
2479 \c int *hatch, float *r, float *g, float *b)
2481 This function is called by the implementations of the drawing API
2482 functions when they are called in a printing context. It takes a
2483 colour index as input, and returns the description of the colour as
2484 requested by the back end.
2486 \c{printincolour} is \cw{TRUE} iff the implementation is printing in
2487 colour. This will alter the results returned if the colour in
2488 question was specified with a black-and-white fallback value.
2490 If the colour should be rendered by hatching, \c{*hatch} is filled
2491 with the type of hatching desired. See \k{print-grey-colour} for
2492 details of the values this integer can take.
2494 If the colour should be rendered as solid colour, \c{*hatch} is
2495 given a negative value, and \c{*r}, \c{*g} and \c{*b} are filled
2496 with the RGB values of the desired colour (if printing in colour),
2497 or all filled with the grey-scale value (if printing in black and
2500 \C{midend} The API provided by the mid-end
2502 This chapter documents the API provided by the mid-end to be called
2503 by the front end. You probably only need to read this if you are a
2504 front end implementor, i.e. you are porting Puzzles to a new
2505 platform. If you're only interested in writing new puzzles, you can
2506 safely skip this chapter.
2508 All the persistent state in the mid-end is encapsulated within a
2509 \c{midend} structure, to facilitate having multiple mid-ends in any
2510 port which supports multiple puzzle windows open simultaneously.
2511 Each \c{midend} is intended to handle the contents of a single
2514 \H{midend-new} \cw{midend_new()}
2516 \c midend *midend_new(frontend *fe, const game *ourgame,
2517 \c const drawing_api *drapi, void *drhandle)
2519 Allocates and returns a new mid-end structure.
2521 The \c{fe} argument is stored in the mid-end. It will be used when
2522 calling back to functions such as \cw{activate_timer()}
2523 (\k{frontend-activate-timer}), and will be passed on to the back end
2524 function \cw{colours()} (\k{backend-colours}).
2526 The parameters \c{drapi} and \c{drhandle} are passed to
2527 \cw{drawing_new()} (\k{drawing-new}) to construct a drawing object
2528 which will be passed to the back end function \cw{redraw()}
2529 (\k{backend-redraw}). Hence, all drawing-related function pointers
2530 defined in \c{drapi} can expect to be called with \c{drhandle} as
2531 their first argument.
2533 The \c{ourgame} argument points to a container structure describing
2534 a game back end. The mid-end thus created will only be capable of
2535 handling that one game. (So even in a monolithic front end
2536 containing all the games, this imposes the constraint that any
2537 individual puzzle window is tied to a single game. Unless, of
2538 course, you feel brave enough to change the mid-end for the window
2539 without closing the window...)
2541 \H{midend-free} \cw{midend_free()}
2543 \c void midend_free(midend *me);
2545 Frees a mid-end structure and all its associated data.
2549 \c int midend_tilesize(midend *me);
2551 Returns the \cq{tilesize} parameter being used to display the
2554 \k{backend-preferred-tilesize}
2556 \H{midend-set-params} \cw{midend_set_params()}
2558 \c void midend_set_params(midend *me, game_params *params);
2560 Sets the current game parameters for a mid-end. Subsequent games
2561 generated by \cw{midend_new_game()} (\k{midend-new-game}) will use
2562 these parameters until further notice.
2564 The usual way in which the front end will have an actual
2565 \c{game_params} structure to pass to this function is if it had
2566 previously got it from \cw{midend_fetch_preset()}
2567 (\k{midend-fetch-preset}). Thus, this function is usually called in
2568 response to the user making a selection from the presets menu.
2570 \H{midend-get-params} \cw{midend_get_params()}
2572 \c game_params *midend_get_params(midend *me);
2574 Returns the current game parameters stored in this mid-end.
2576 The returned value is dynamically allocated, and should be freed
2577 when finished with by passing it to the game's own
2578 \cw{free_params()} function (see \k{backend-free-params}).
2580 \H{midend-size} \cw{midend_size()}
2582 \c void midend_size(midend *me, int *x, int *y, int user_size);
2584 Tells the mid-end to figure out its window size.
2586 On input, \c{*x} and \c{*y} should contain the maximum or requested
2587 size for the window. (Typically this will be the size of the screen
2588 that the window has to fit on, or similar.) The mid-end will
2589 repeatedly call the back end function \cw{compute_size()}
2590 (\k{backend-compute-size}), searching for a tile size that best
2591 satisfies the requirements. On exit, \c{*x} and \c{*y} will contain
2592 the size needed for the puzzle window's drawing area. (It is of
2593 course up to the front end to adjust this for any additional window
2594 furniture such as menu bars and window borders, if necessary. The
2595 status bar is also not included in this size.)
2597 Use \c{user_size} to indicate whether \c{*x} and \c{*y} are a
2598 requested size, or just a maximum size.
2600 If \c{user_size} is set to \cw{TRUE}, the mid-end will treat the
2601 input size as a request, and will pick a tile size which
2602 approximates it \e{as closely as possible}, going over the game's
2603 preferred tile size if necessary to achieve this. The mid-end will
2604 also use the resulting tile size as its preferred one until further
2605 notice, on the assumption that this size was explicitly requested
2606 by the user. Use this option if you want your front end to support
2607 dynamic resizing of the puzzle window with automatic scaling of the
2610 If \c{user_size} is set to \cw{FALSE}, then the game's tile size
2611 will never go over its preferred one, although it may go under in
2612 order to fit within the maximum bounds specified by \c{*x} and
2613 \c{*y}. This is the recommended approach when opening a new window
2614 at default size: the game will use its preferred size unless it has
2615 to use a smaller one to fit on the screen. If the tile size is
2616 shrunk for this reason, the change will not persist; if a smaller
2617 grid is subsequently chosen, the tile size will recover.
2619 The mid-end will try as hard as it can to return a size which is
2620 less than or equal to the input size, in both dimensions. In extreme
2621 circumstances it may fail (if even the lowest possible tile size
2622 gives window dimensions greater than the input), in which case it
2623 will return a size greater than the input size. Front ends should be
2624 prepared for this to happen (i.e. don't crash or fail an assertion),
2625 but may handle it in any way they see fit: by rejecting the game
2626 parameters which caused the problem, by opening a window larger than
2627 the screen regardless of inconvenience, by introducing scroll bars
2628 on the window, by drawing on a large bitmap and scaling it into a
2629 smaller window, or by any other means you can think of. It is likely
2630 that when the tile size is that small the game will be unplayable
2631 anyway, so don't put \e{too} much effort into handling it
2634 If your platform has no limit on window size (or if you're planning
2635 to use scroll bars for large puzzles), you can pass dimensions of
2636 \cw{INT_MAX} as input to this function. You should probably not do
2637 that \e{and} set the \c{user_size} flag, though!
2639 \H{midend-new-game} \cw{midend_new_game()}
2641 \c void midend_new_game(midend *me);
2643 Causes the mid-end to begin a new game. Normally the game will be a
2644 new randomly generated puzzle. However, if you have previously
2645 called \cw{midend_game_id()} or \cw{midend_set_config()}, the game
2646 generated might be dictated by the results of those functions. (In
2647 particular, you \e{must} call \cw{midend_new_game()} after calling
2648 either of those functions, or else no immediate effect will be
2651 You will probably need to call \cw{midend_size()} after calling this
2652 function, because if the game parameters have been changed since the
2653 last new game then the window size might need to change. (If you
2654 know the parameters \e{haven't} changed, you don't need to do this.)
2656 This function will create a new \c{game_drawstate}, but does not
2657 actually perform a redraw (since you often need to call
2658 \cw{midend_size()} before the redraw can be done). So after calling
2659 this function and after calling \cw{midend_size()}, you should then
2660 call \cw{midend_redraw()}. (It is not necessary to call
2661 \cw{midend_force_redraw()}; that will discard the draw state and
2662 create a fresh one, which is unnecessary in this case since there's
2663 a fresh one already. It would work, but it's usually excessive.)
2665 \H{midend-restart-game} \cw{midend_restart_game()}
2667 \c void midend_restart_game(midend *me);
2669 This function causes the current game to be restarted. This is done
2670 by placing a new copy of the original game state on the end of the
2671 undo list (so that an accidental restart can be undone).
2673 This function automatically causes a redraw, i.e. the front end can
2674 expect its drawing API to be called from \e{within} a call to this
2677 \H{midend-force-redraw} \cw{midend_force_redraw()}
2679 \c void midend_force_redraw(midend *me);
2681 Forces a complete redraw of the puzzle window, by means of
2682 discarding the current \c{game_drawstate} and creating a new one
2683 from scratch before calling the game's \cw{redraw()} function.
2685 The front end can expect its drawing API to be called from within a
2686 call to this function.
2688 \H{midend-redraw} \cw{midend_redraw()}
2690 \c void midend_redraw(midend *me);
2692 Causes a partial redraw of the puzzle window, by means of simply
2693 calling the game's \cw{redraw()} function. (That is, the only things
2694 redrawn will be things that have changed since the last redraw.)
2696 The front end can expect its drawing API to be called from within a
2697 call to this function.
2699 \H{midend-process-key} \cw{midend_process_key()}
2701 \c int midend_process_key(midend *me, int x, int y, int button);
2703 The front end calls this function to report a mouse or keyboard
2704 event. The parameters \c{x}, \c{y} and \c{button} are almost
2705 identical to the ones passed to the back end function
2706 \cw{interpret_move()} (\k{backend-interpret-move}), except that the
2707 front end is \e{not} required to provide the guarantees about mouse
2708 event ordering. The mid-end will sort out multiple simultaneous
2709 button presses and changes of button; the front end's responsibility
2710 is simply to pass on the mouse events it receives as accurately as
2713 (Some platforms may need to emulate absent mouse buttons by means of
2714 using a modifier key such as Shift with another mouse button. This
2715 tends to mean that if Shift is pressed or released in the middle of
2716 a mouse drag, the mid-end will suddenly stop receiving, say,
2717 \cw{LEFT_DRAG} events and start receiving \cw{RIGHT_DRAG}s, with no
2718 intervening button release or press events. This too is something
2719 which the mid-end will sort out for you; the front end has no
2720 obligation to maintain sanity in this area.)
2722 The front end \e{should}, however, always eventually send some kind
2723 of button release. On some platforms this requires special effort:
2724 Windows, for example, requires a call to the system API function
2725 \cw{SetCapture()} in order to ensure that your window receives a
2726 mouse-up event even if the pointer has left the window by the time
2727 the mouse button is released. On any platform that requires this
2728 sort of thing, the front end \e{is} responsible for doing it.
2730 Calling this function is very likely to result in calls back to the
2731 front end's drawing API and/or \cw{activate_timer()}
2732 (\k{frontend-activate-timer}).
2734 The return value from \cw{midend_process_key()} is non-zero, unless
2735 the effect of the keypress was to request termination of the
2736 program. A front end should shut down the puzzle in response to a
2739 \H{midend-colours} \cw{midend_colours()}
2741 \c float *midend_colours(midend *me, int *ncolours);
2743 Returns an array of the colours required by the game, in exactly the
2744 same format as that returned by the back end function \cw{colours()}
2745 (\k{backend-colours}). Front ends should call this function rather
2746 than calling the back end's version directly, since the mid-end adds
2747 standard customisation facilities. (At the time of writing, those
2748 customisation facilities are implemented hackily by means of
2749 environment variables, but it's not impossible that they may become
2750 more full and formal in future.)
2752 \H{midend-timer} \cw{midend_timer()}
2754 \c void midend_timer(midend *me, float tplus);
2756 If the mid-end has called \cw{activate_timer()}
2757 (\k{frontend-activate-timer}) to request regular callbacks for
2758 purposes of animation or timing, this is the function the front end
2759 should call on a regular basis. The argument \c{tplus} gives the
2760 time, in seconds, since the last time either this function was
2761 called or \cw{activate_timer()} was invoked.
2763 One of the major purposes of timing in the mid-end is to perform
2764 move animation. Therefore, calling this function is very likely to
2765 result in calls back to the front end's drawing API.
2767 \H{midend-num-presets} \cw{midend_num_presets()}
2769 \c int midend_num_presets(midend *me);
2771 Returns the number of game parameter presets supplied by this game.
2772 Front ends should use this function and \cw{midend_fetch_preset()}
2773 to configure their presets menu rather than calling the back end
2774 directly, since the mid-end adds standard customisation facilities.
2775 (At the time of writing, those customisation facilities are
2776 implemented hackily by means of environment variables, but it's not
2777 impossible that they may become more full and formal in future.)
2779 \H{midend-fetch-preset} \cw{midend_fetch_preset()}
2781 \c void midend_fetch_preset(midend *me, int n,
2782 \c char **name, game_params **params);
2784 Returns one of the preset game parameter structures for the game. On
2785 input \c{n} must be a non-negative integer and less than the value
2786 returned from \cw{midend_num_presets()}. On output, \c{*name} is set
2787 to an ASCII string suitable for entering in the game's presets menu,
2788 and \c{*params} is set to the corresponding \c{game_params}
2791 Both of the two output values are dynamically allocated, but they
2792 are owned by the mid-end structure: the front end should not ever
2793 free them directly, because they will be freed automatically during
2796 \H{midend-which-preset} \cw{midend_which_preset()}
2798 \c int midend_which_preset(midend *me);
2800 Returns the numeric index of the preset game parameter structure
2801 which matches the current game parameters, or a negative number if
2802 no preset matches. Front ends could use this to maintain a tick
2803 beside one of the items in the menu (or tick the \q{Custom} option
2804 if the return value is less than zero).
2806 \H{midend-wants-statusbar} \cw{midend_wants_statusbar()}
2808 \c int midend_wants_statusbar(midend *me);
2810 This function returns \cw{TRUE} if the puzzle has a use for a
2811 textual status line (to display score, completion status, currently
2812 active tiles, time, or anything else).
2814 Front ends should call this function rather than talking directly to
2817 \H{midend-get-config} \cw{midend_get_config()}
2819 \c config_item *midend_get_config(midend *me, int which,
2820 \c char **wintitle);
2822 Returns a dialog box description for user configuration.
2824 On input, \cw{which} should be set to one of three values, which
2825 select which of the various dialog box descriptions is returned:
2827 \dt \cw{CFG_SETTINGS}
2829 \dd Requests the GUI parameter configuration box generated by the
2830 puzzle itself. This should be used when the user selects \q{Custom}
2831 from the game types menu (or equivalent). The mid-end passes this
2832 request on to the back end function \cw{configure()}
2833 (\k{backend-configure}).
2837 \dd Requests a box suitable for entering a descriptive game ID (and
2838 viewing the existing one). The mid-end generates this dialog box
2839 description itself. This should be used when the user selects
2840 \q{Specific} from the game menu (or equivalent).
2844 \dd Requests a box suitable for entering a random-seed game ID (and
2845 viewing the existing one). The mid-end generates this dialog box
2846 description itself. This should be used when the user selects
2847 \q{Random Seed} from the game menu (or equivalent).
2849 The returned value is an array of \cw{config_item}s, exactly as
2850 described in \k{backend-configure}. Another returned value is an
2851 ASCII string giving a suitable title for the configuration window,
2854 Both returned values are dynamically allocated and will need to be
2855 freed. The window title can be freed in the obvious way; the
2856 \cw{config_item} array is a slightly complex structure, so a utility
2857 function \cw{free_cfg()} is provided to free it for you. See
2860 (Of course, you will probably not want to free the \cw{config_item}
2861 array until the dialog box is dismissed, because before then you
2862 will probably need to pass it to \cw{midend_set_config}.)
2864 \H{midend-set-config} \cw{midend_set_config()}
2866 \c char *midend_set_config(midend *me, int which,
2867 \c config_item *cfg);
2869 Passes the mid-end the results of a configuration dialog box.
2870 \c{which} should have the same value which it had when
2871 \cw{midend_get_config()} was called; \c{cfg} should be the array of
2872 \c{config_item}s returned from \cw{midend_get_config()}, modified to
2873 contain the results of the user's editing operations.
2875 This function returns \cw{NULL} on success, or otherwise (if the
2876 configuration data was in some way invalid) an ASCII string
2877 containing an error message suitable for showing to the user.
2879 If the function succeeds, it is likely that the game parameters will
2880 have been changed and it is certain that a new game will be
2881 requested. The front end should therefore call
2882 \cw{midend_new_game()}, and probably also re-think the window size
2883 using \cw{midend_size()} and eventually perform a refresh using
2884 \cw{midend_redraw()}.
2886 \H{midend-game-id} \cw{midend_game_id()}
2888 \c char *midend_game_id(midend *me, char *id);
2890 Passes the mid-end a string game ID (of any of the valid forms
2891 \cq{params}, \cq{params:description} or \cq{params#seed}) which the
2892 mid-end will process and use for the next generated game.
2894 This function returns \cw{NULL} on success, or otherwise (if the
2895 configuration data was in some way invalid) an ASCII string
2896 containing an error message (not dynamically allocated) suitable for
2897 showing to the user. In the event of an error, the mid-end's
2898 internal state will be left exactly as it was before the call.
2900 If the function succeeds, it is likely that the game parameters will
2901 have been changed and it is certain that a new game will be
2902 requested. The front end should therefore call
2903 \cw{midend_new_game()}, and probably also re-think the window size
2904 using \cw{midend_size()} and eventually case a refresh using
2905 \cw{midend_redraw()}.
2907 \H{midend-get-game-id} \cw{midend_get_game_id()}
2909 \c char *midend_get_game_id(midend *me)
2911 Returns a descriptive game ID (i.e. one in the form
2912 \cq{params:description}) describing the game currently active in the
2913 mid-end. The returned string is dynamically allocated.
2915 \H{midend-can-format-as-text-now} \cw{midend_can_format_as_text_now()}
2917 \c int midend_can_format_as_text_now(midend *me);
2919 Returns \cw{TRUE} if the game code is capable of formatting puzzles
2920 of the currently selected game type as ASCII.
2922 If this returns \cw{FALSE}, then \cw{midend_text_format()}
2923 (\k{midend-text-format}) will return \cw{NULL}.
2925 \H{midend-text-format} \cw{midend_text_format()}
2927 \c char *midend_text_format(midend *me);
2929 Formats the current game's current state as ASCII text suitable for
2930 copying to the clipboard. The returned string is dynamically
2933 If the game's \c{can_format_as_text_ever} flag is \cw{FALSE}, or if
2934 its \cw{can_format_as_text_now()} function returns \cw{FALSE}, then
2935 this function will return \cw{NULL}.
2937 If the returned string contains multiple lines (which is likely), it
2938 will use the normal C line ending convention (\cw{\\n} only). On
2939 platforms which use a different line ending convention for data in
2940 the clipboard, it is the front end's responsibility to perform the
2943 \H{midend-solve} \cw{midend_solve()}
2945 \c char *midend_solve(midend *me);
2947 Requests the mid-end to perform a Solve operation.
2949 On success, \cw{NULL} is returned. On failure, an error message (not
2950 dynamically allocated) is returned, suitable for showing to the
2953 The front end can expect its drawing API and/or
2954 \cw{activate_timer()} to be called from within a call to this
2957 \H{midend-serialise} \cw{midend_serialise()}
2959 \c void midend_serialise(midend *me,
2960 \c void (*write)(void *ctx, void *buf, int len),
2963 Calling this function causes the mid-end to convert its entire
2964 internal state into a long ASCII text string, and to pass that
2965 string (piece by piece) to the supplied \c{write} function.
2967 Desktop implementations can use this function to save a game in any
2968 state (including half-finished) to a disk file, by supplying a
2969 \c{write} function which is a wrapper on \cw{fwrite()} (or local
2970 equivalent). Other implementations may find other uses for it, such
2971 as compressing the large and sprawling mid-end state into a
2972 manageable amount of memory when a palmtop application is suspended
2973 so that another one can run; in this case \cw{write} might want to
2974 write to a memory buffer rather than a file. There may be other uses
2977 This function will call back to the supplied \c{write} function a
2978 number of times, with the first parameter (\c{ctx}) equal to
2979 \c{wctx}, and the other two parameters pointing at a piece of the
2982 \H{midend-deserialise} \cw{midend_deserialise()}
2984 \c char *midend_deserialise(midend *me,
2985 \c int (*read)(void *ctx, void *buf, int len),
2988 This function is the counterpart to \cw{midend_serialise()}. It
2989 calls the supplied \cw{read} function repeatedly to read a quantity
2990 of data, and attempts to interpret that data as a serialised mid-end
2991 as output by \cw{midend_serialise()}.
2993 The \cw{read} function is called with the first parameter (\c{ctx})
2994 equal to \c{rctx}, and should attempt to read \c{len} bytes of data
2995 into the buffer pointed to by \c{buf}. It should return \cw{FALSE}
2996 on failure or \cw{TRUE} on success. It should not report success
2997 unless it has filled the entire buffer; on platforms which might be
2998 reading from a pipe or other blocking data source, \c{read} is
2999 responsible for looping until the whole buffer has been filled.
3001 If the de-serialisation operation is successful, the mid-end's
3002 internal data structures will be replaced by the results of the
3003 load, and \cw{NULL} will be returned. Otherwise, the mid-end's state
3004 will be completely unchanged and an error message (typically some
3005 variation on \q{save file is corrupt}) will be returned. As usual,
3006 the error message string is not dynamically allocated.
3008 If this function succeeds, it is likely that the game parameters
3009 will have been changed. The front end should therefore probably
3010 re-think the window size using \cw{midend_size()}, and probably
3011 cause a refresh using \cw{midend_redraw()}.
3013 Because each mid-end is tied to a specific game back end, this
3014 function will fail if you attempt to read in a save file generated
3015 by a different game from the one configured in this mid-end, even if
3016 your application is a monolithic one containing all the puzzles. (It
3017 would be pretty easy to write a function which would look at a save
3018 file and determine which game it was for; any front end implementor
3019 who needs such a function can probably be accommodated.)
3021 \H{frontend-backend} Direct reference to the back end structure by
3024 Although \e{most} things the front end needs done should be done by
3025 calling the mid-end, there are a few situations in which the front
3026 end needs to refer directly to the game back end structure.
3028 The most obvious of these is
3030 \b passing the game back end as a parameter to \cw{midend_new()}.
3032 There are a few other back end features which are not wrapped by the
3033 mid-end because there didn't seem much point in doing so:
3035 \b fetching the \c{name} field to use in window titles and similar
3037 \b reading the \c{can_configure}, \c{can_solve} and
3038 \c{can_format_as_text_ever} fields to decide whether to add those
3039 items to the menu bar or equivalent
3041 \b reading the \c{winhelp_topic} field (Windows only)
3043 \b the GTK front end provides a \cq{--generate} command-line option
3044 which directly calls the back end to do most of its work. This is
3045 not really part of the main front end code, though, and I'm not sure
3048 In order to find the game back end structure, the front end does one
3051 \b If the particular front end is compiling a separate binary per
3052 game, then the back end structure is a global variable with the
3053 standard name \cq{thegame}:
3057 \c extern const game thegame;
3061 \b If the front end is compiled as a monolithic application
3062 containing all the puzzles together (in which case the preprocessor
3063 symbol \cw{COMBINED} must be defined when compiling most of the code
3064 base), then there will be two global variables defined:
3068 \c extern const game *gamelist[];
3069 \c extern const int gamecount;
3071 \c{gamelist} will be an array of \c{gamecount} game structures,
3072 declared in the automatically constructed source module \c{list.c}.
3073 The application should search that array for the game it wants,
3074 probably by reaching into each game structure and looking at its
3079 \H{frontend-api} Mid-end to front-end calls
3081 This section describes the small number of functions which a front
3082 end must provide to be called by the mid-end or other standard
3085 \H{frontend-get-random-seed} \cw{get_random_seed()}
3087 \c void get_random_seed(void **randseed, int *randseedsize);
3089 This function is called by a new mid-end, and also occasionally by
3090 game back ends. Its job is to return a piece of data suitable for
3091 using as a seed for initialisation of a new \c{random_state}.
3093 On exit, \c{*randseed} should be set to point at a newly allocated
3094 piece of memory containing some seed data, and \c{*randseedsize}
3095 should be set to the length of that data.
3097 A simple and entirely adequate implementation is to return a piece
3098 of data containing the current system time at the highest
3099 conveniently available resolution.
3101 \H{frontend-activate-timer} \cw{activate_timer()}
3103 \c void activate_timer(frontend *fe);
3105 This is called by the mid-end to request that the front end begin
3106 calling it back at regular intervals.
3108 The timeout interval is left up to the front end; the finer it is,
3109 the smoother move animations will be, but the more CPU time will be
3110 used. Current front ends use values around 20ms (i.e. 50Hz).
3112 After this function is called, the mid-end will expect to receive
3113 calls to \cw{midend_timer()} on a regular basis.
3115 \H{frontend-deactivate-timer} \cw{deactivate_timer()}
3117 \c void deactivate_timer(frontend *fe);
3119 This is called by the mid-end to request that the front end stop
3120 calling \cw{midend_timer()}.
3122 \H{frontend-fatal} \cw{fatal()}
3124 \c void fatal(char *fmt, ...);
3126 This is called by some utility functions if they encounter a
3127 genuinely fatal error such as running out of memory. It is a
3128 variadic function in the style of \cw{printf()}, and is expected to
3129 show the formatted error message to the user any way it can and then
3130 terminate the application. It must not return.
3132 \H{frontend-default-colour} \cw{frontend_default_colour()}
3134 \c void frontend_default_colour(frontend *fe, float *output);
3136 This function expects to be passed a pointer to an array of three
3137 \cw{float}s. It returns the platform's local preferred background
3138 colour in those three floats, as red, green and blue values (in that
3139 order) ranging from \cw{0.0} to \cw{1.0}.
3141 This function should only ever be called by the back end function
3142 \cw{colours()} (\k{backend-colours}). (Thus, it isn't a
3143 \e{midend}-to-frontend function as such, but there didn't seem to be
3144 anywhere else particularly good to put it. Sorry.)
3146 \C{utils} Utility APIs
3148 This chapter documents a variety of utility APIs provided for the
3149 general use of the rest of the Puzzles code.
3151 \H{utils-random} Random number generation
3153 Platforms' local random number generators vary widely in quality and
3154 seed size. Puzzles therefore supplies its own high-quality random
3155 number generator, with the additional advantage of giving the same
3156 results if fed the same seed data on different platforms. This
3157 allows game random seeds to be exchanged between different ports of
3158 Puzzles and still generate the same games.
3160 Unlike the ANSI C \cw{rand()} function, the Puzzles random number
3161 generator has an \e{explicit} state object called a
3162 \c{random_state}. One of these is managed by each mid-end, for
3163 example, and passed to the back end to generate a game with.
3165 \S{utils-random-init} \cw{random_new()}
3167 \c random_state *random_new(char *seed, int len);
3169 Allocates, initialises and returns a new \c{random_state}. The input
3170 data is used as the seed for the random number stream (i.e. using
3171 the same seed at a later time will generate the same stream).
3173 The seed data can be any data at all; there is no requirement to use
3174 printable ASCII, or NUL-terminated strings, or anything like that.
3176 \S{utils-random-copy} \cw{random_copy()}
3178 \c random_state *random_copy(random_state *tocopy);
3180 Allocates a new \c{random_state}, copies the contents of another
3181 \c{random_state} into it, and returns the new state. If exactly the
3182 same sequence of functions is subseqently called on both the copy and
3183 the original, the results will be identical. This may be useful for
3184 speculatively performing some operation using a given random state,
3185 and later replaying that operation precisely.
3187 \S{utils-random-free} \cw{random_free()}
3189 \c void random_free(random_state *state);
3191 Frees a \c{random_state}.
3193 \S{utils-random-bits} \cw{random_bits()}
3195 \c unsigned long random_bits(random_state *state, int bits);
3197 Returns a random number from 0 to \cw{2^bits-1} inclusive. \c{bits}
3198 should be between 1 and 32 inclusive.
3200 \S{utils-random-upto} \cw{random_upto()}
3202 \c unsigned long random_upto(random_state *state, unsigned long limit);
3204 Returns a random number from 0 to \cw{limit-1} inclusive.
3206 \S{utils-random-state-encode} \cw{random_state_encode()}
3208 \c char *random_state_encode(random_state *state);
3210 Encodes the entire contents of a \c{random_state} in printable
3211 ASCII. Returns a dynamically allocated string containing that
3212 encoding. This can subsequently be passed to
3213 \cw{random_state_decode()} to reconstruct the same \c{random_state}.
3215 \S{utils-random-state-decode} \cw{random_state_decode()}
3217 \c random_state *random_state_decode(char *input);
3219 Decodes a string generated by \cw{random_state_encode()} and
3220 reconstructs an equivalent \c{random_state} to the one encoded, i.e.
3221 it should produce the same stream of random numbers.
3223 This function has no error reporting; if you pass it an invalid
3224 string it will simply generate an arbitrary random state, which may
3225 turn out to be noticeably non-random.
3227 \S{utils-shuffle} \cw{shuffle()}
3229 \c void shuffle(void *array, int nelts, int eltsize, random_state *rs);
3231 Shuffles an array into a random order. The interface is much like
3232 ANSI C \cw{qsort()}, except that there's no need for a compare
3235 \c{array} is a pointer to the first element of the array. \c{nelts}
3236 is the number of elements in the array; \c{eltsize} is the size of a
3237 single element (typically measured using \c{sizeof}). \c{rs} is a
3238 \c{random_state} used to generate all the random numbers for the
3241 \H{utils-alloc} Memory allocation
3243 Puzzles has some central wrappers on the standard memory allocation
3244 functions, which provide compile-time type checking, and run-time
3245 error checking by means of quitting the application if it runs out
3246 of memory. This doesn't provide the best possible recovery from
3247 memory shortage, but on the other hand it greatly simplifies the
3248 rest of the code, because nothing else anywhere needs to worry about
3249 \cw{NULL} returns from allocation.
3251 \S{utils-snew} \cw{snew()}
3253 \c var = snew(type);
3256 This macro takes a single argument which is a \e{type name}. It
3257 allocates space for one object of that type. If allocation fails it
3258 will call \cw{fatal()} and not return; so if it does return, you can
3259 be confident that its return value is non-\cw{NULL}.
3261 The return value is cast to the specified type, so that the compiler
3262 will type-check it against the variable you assign it into. Thus,
3263 this ensures you don't accidentally allocate memory the size of the
3264 wrong type and assign it into a variable of the right one (or vice
3267 \S{utils-snewn} \cw{snewn()}
3269 \c var = snewn(n, type);
3272 This macro is the array form of \cw{snew()}. It takes two arguments;
3273 the first is a number, and the second is a type name. It allocates
3274 space for that many objects of that type, and returns a type-checked
3275 non-\cw{NULL} pointer just as \cw{snew()} does.
3277 \S{utils-sresize} \cw{sresize()}
3279 \c var = sresize(var, n, type);
3282 This macro is a type-checked form of \cw{realloc()}. It takes three
3283 arguments: an input memory block, a new size in elements, and a
3284 type. It re-sizes the input memory block to a size sufficient to
3285 contain that many elements of that type. It returns a type-checked
3286 non-\cw{NULL} pointer, like \cw{snew()} and \cw{snewn()}.
3288 The input memory block can be \cw{NULL}, in which case this function
3289 will behave exactly like \cw{snewn()}. (In principle any
3290 ANSI-compliant \cw{realloc()} implementation ought to cope with
3291 this, but I've never quite trusted it to work everywhere.)
3293 \S{utils-sfree} \cw{sfree()}
3295 \c void sfree(void *p);
3297 This function is pretty much equivalent to \cw{free()}. It is
3298 provided with a dynamically allocated block, and frees it.
3300 The input memory block can be \cw{NULL}, in which case this function
3301 will do nothing. (In principle any ANSI-compliant \cw{free()}
3302 implementation ought to cope with this, but I've never quite trusted
3303 it to work everywhere.)
3305 \S{utils-dupstr} \cw{dupstr()}
3307 \c char *dupstr(const char *s);
3309 This function dynamically allocates a duplicate of a C string. Like
3310 the \cw{snew()} functions, it guarantees to return non-\cw{NULL} or
3313 (Many platforms provide the function \cw{strdup()}. As well as
3314 guaranteeing never to return \cw{NULL}, my version has the advantage
3315 of being defined \e{everywhere}, rather than inconveniently not
3318 \S{utils-free-cfg} \cw{free_cfg()}
3320 \c void free_cfg(config_item *cfg);
3322 This function correctly frees an array of \c{config_item}s,
3323 including walking the array until it gets to the end and freeing
3324 precisely those \c{sval} fields which are expected to be dynamically
3327 (See \k{backend-configure} for details of the \c{config_item}
3330 \H{utils-tree234} Sorted and counted tree functions
3332 Many games require complex algorithms for generating random puzzles,
3333 and some require moderately complex algorithms even during play. A
3334 common requirement during these algorithms is for a means of
3335 maintaining sorted or unsorted lists of items, such that items can
3336 be removed and added conveniently.
3338 For general use, Puzzles provides the following set of functions
3339 which maintain 2-3-4 trees in memory. (A 2-3-4 tree is a balanced
3340 tree structure, with the property that all lookups, insertions,
3341 deletions, splits and joins can be done in \cw{O(log N)} time.)
3343 All these functions expect you to be storing a tree of \c{void *}
3344 pointers. You can put anything you like in those pointers.
3346 By the use of per-node element counts, these tree structures have
3347 the slightly unusual ability to look elements up by their numeric
3348 index within the list represented by the tree. This means that they
3349 can be used to store an unsorted list (in which case, every time you
3350 insert a new element, you must explicitly specify the position where
3351 you wish to insert it). They can also do numeric lookups in a sorted
3352 tree, which might be useful for (for example) tracking the median of
3353 a changing data set.
3355 As well as storing sorted lists, these functions can be used for
3356 storing \q{maps} (associative arrays), by defining each element of a
3357 tree to be a (key, value) pair.
3359 \S{utils-newtree234} \cw{newtree234()}
3361 \c tree234 *newtree234(cmpfn234 cmp);
3363 Creates a new empty tree, and returns a pointer to it.
3365 The parameter \c{cmp} determines the sorting criterion on the tree.
3368 \c typedef int (*cmpfn234)(void *, void *);
3370 If you want a sorted tree, you should provide a function matching
3371 this prototype, which returns like \cw{strcmp()} does (negative if
3372 the first argument is smaller than the second, positive if it is
3373 bigger, zero if they compare equal). In this case, the function
3374 \cw{addpos234()} will not be usable on your tree (because all
3375 insertions must respect the sorting order).
3377 If you want an unsorted tree, pass \cw{NULL}. In this case you will
3378 not be able to use either \cw{add234()} or \cw{del234()}, or any
3379 other function such as \cw{find234()} which depends on a sorting
3380 order. Your tree will become something more like an array, except
3381 that it will efficiently support insertion and deletion as well as
3382 lookups by numeric index.
3384 \S{utils-freetree234} \cw{freetree234()}
3386 \c void freetree234(tree234 *t);
3388 Frees a tree. This function will not free the \e{elements} of the
3389 tree (because they might not be dynamically allocated, or you might
3390 be storing the same set of elements in more than one tree); it will
3391 just free the tree structure itself. If you want to free all the
3392 elements of a tree, you should empty it before passing it to
3393 \cw{freetree234()}, by means of code along the lines of
3395 \c while ((element = delpos234(tree, 0)) != NULL)
3396 \c sfree(element); /* or some more complicated free function */
3397 \e iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii
3399 \S{utils-add234} \cw{add234()}
3401 \c void *add234(tree234 *t, void *e);
3403 Inserts a new element \c{e} into the tree \c{t}. This function
3404 expects the tree to be sorted; the new element is inserted according
3407 If an element comparing equal to \c{e} is already in the tree, then
3408 the insertion will fail, and the return value will be the existing
3409 element. Otherwise, the insertion succeeds, and \c{e} is returned.
3411 \S{utils-addpos234} \cw{addpos234()}
3413 \c void *addpos234(tree234 *t, void *e, int index);
3415 Inserts a new element into an unsorted tree. Since there is no
3416 sorting order to dictate where the new element goes, you must
3417 specify where you want it to go. Setting \c{index} to zero puts the
3418 new element right at the start of the list; setting \c{index} to the
3419 current number of elements in the tree puts the new element at the
3422 Return value is \c{e}, in line with \cw{add234()} (although this
3423 function cannot fail except by running out of memory, in which case
3424 it will bomb out and die rather than returning an error indication).
3426 \S{utils-index234} \cw{index234()}
3428 \c void *index234(tree234 *t, int index);
3430 Returns a pointer to the \c{index}th element of the tree, or
3431 \cw{NULL} if \c{index} is out of range. Elements of the tree are
3434 \S{utils-find234} \cw{find234()}
3436 \c void *find234(tree234 *t, void *e, cmpfn234 cmp);
3438 Searches for an element comparing equal to \c{e} in a sorted tree.
3440 If \c{cmp} is \cw{NULL}, the tree's ordinary comparison function
3441 will be used to perform the search. However, sometimes you don't
3442 want that; suppose, for example, each of your elements is a big
3443 structure containing a \c{char *} name field, and you want to find
3444 the element with a given name. You \e{could} achieve this by
3445 constructing a fake element structure, setting its name field
3446 appropriately, and passing it to \cw{find234()}, but you might find
3447 it more convenient to pass \e{just} a name string to \cw{find234()},
3448 supplying an alternative comparison function which expects one of
3449 its arguments to be a bare name and the other to be a large
3450 structure containing a name field.
3452 Therefore, if \c{cmp} is not \cw{NULL}, then it will be used to
3453 compare \c{e} to elements of the tree. The first argument passed to
3454 \c{cmp} will always be \c{e}; the second will be an element of the
3457 (See \k{utils-newtree234} for the definition of the \c{cmpfn234}
3458 function pointer type.)
3460 The returned value is the element found, or \cw{NULL} if the search
3463 \S{utils-findrel234} \cw{findrel234()}
3465 \c void *findrel234(tree234 *t, void *e, cmpfn234 cmp, int relation);
3467 This function is like \cw{find234()}, but has the additional ability
3468 to do a \e{relative} search. The additional parameter \c{relation}
3469 can be one of the following values:
3473 \dd Find only an element that compares equal to \c{e}. This is
3474 exactly the behaviour of \cw{find234()}.
3478 \dd Find the greatest element that compares strictly less than
3479 \c{e}. \c{e} may be \cw{NULL}, in which case it finds the greatest
3480 element in the whole tree (which could also be done by
3481 \cw{index234(t, count234(t)-1)}).
3485 \dd Find the greatest element that compares less than or equal to
3486 \c{e}. (That is, find an element that compares equal to \c{e} if
3487 possible, but failing that settle for something just less than it.)
3491 \dd Find the smallest element that compares strictly greater than
3492 \c{e}. \c{e} may be \cw{NULL}, in which case it finds the smallest
3493 element in the whole tree (which could also be done by
3494 \cw{index234(t, 0)}).
3498 \dd Find the smallest element that compares greater than or equal to
3499 \c{e}. (That is, find an element that compares equal to \c{e} if
3500 possible, but failing that settle for something just bigger than
3503 Return value, as before, is the element found or \cw{NULL} if no
3504 element satisfied the search criterion.
3506 \S{utils-findpos234} \cw{findpos234()}
3508 \c void *findpos234(tree234 *t, void *e, cmpfn234 cmp, int *index);
3510 This function is like \cw{find234()}, but has the additional feature
3511 of returning the index of the element found in the tree; that index
3512 is written to \c{*index} in the event of a successful search (a
3513 non-\cw{NULL} return value).
3515 \c{index} may be \cw{NULL}, in which case this function behaves
3516 exactly like \cw{find234()}.
3518 \S{utils-findrelpos234} \cw{findrelpos234()}
3520 \c void *findrelpos234(tree234 *t, void *e, cmpfn234 cmp, int relation,
3523 This function combines all the features of \cw{findrel234()} and
3526 \S{utils-del234} \cw{del234()}
3528 \c void *del234(tree234 *t, void *e);
3530 Finds an element comparing equal to \c{e} in the tree, deletes it,
3533 The input tree must be sorted.
3535 The element found might be \c{e} itself, or might merely compare
3538 Return value is \cw{NULL} if no such element is found.
3540 \S{utils-delpos234} \cw{delpos234()}
3542 \c void *delpos234(tree234 *t, int index);
3544 Deletes the element at position \c{index} in the tree, and returns
3547 Return value is \cw{NULL} if the index is out of range.
3549 \S{utils-count234} \cw{count234()}
3551 \c int count234(tree234 *t);
3553 Returns the number of elements currently in the tree.
3555 \S{utils-splitpos234} \cw{splitpos234()}
3557 \c tree234 *splitpos234(tree234 *t, int index, int before);
3559 Splits the input tree into two pieces at a given position, and
3560 creates a new tree containing all the elements on one side of that
3563 If \c{before} is \cw{TRUE}, then all the items at or after position
3564 \c{index} are left in the input tree, and the items before that
3565 point are returned in the new tree. Otherwise, the reverse happens:
3566 all the items at or after \c{index} are moved into the new tree, and
3567 those before that point are left in the old one.
3569 If \c{index} is equal to 0 or to the number of elements in the input
3570 tree, then one of the two trees will end up empty (and this is not
3571 an error condition). If \c{index} is further out of range in either
3572 direction, the operation will fail completely and return \cw{NULL}.
3574 This operation completes in \cw{O(log N)} time, no matter how large
3575 the tree or how balanced or unbalanced the split.
3577 \S{utils-split234} \cw{split234()}
3579 \c tree234 *split234(tree234 *t, void *e, cmpfn234 cmp, int rel);
3581 Splits a sorted tree according to its sort order.
3583 \c{rel} can be any of the relation constants described in
3584 \k{utils-findrel234}, \e{except} for \cw{REL234_EQ}. All the
3585 elements having that relation to \c{e} will be transferred into the
3586 new tree; the rest will be left in the old one.
3588 The parameter \c{cmp} has the same semantics as it does in
3589 \cw{find234()}: if it is not \cw{NULL}, it will be used in place of
3590 the tree's own comparison function when comparing elements to \c{e},
3591 in such a way that \c{e} itself is always the first of its two
3594 Again, this operation completes in \cw{O(log N)} time, no matter how
3595 large the tree or how balanced or unbalanced the split.
3597 \S{utils-join234} \cw{join234()}
3599 \c tree234 *join234(tree234 *t1, tree234 *t2);
3601 Joins two trees together by concatenating the lists they represent.
3602 All the elements of \c{t2} are moved into \c{t1}, in such a way that
3603 they appear \e{after} the elements of \c{t1}. The tree \c{t2} is
3604 freed; the return value is \c{t1}.
3606 If you apply this function to a sorted tree and it violates the sort
3607 order (i.e. the smallest element in \c{t2} is smaller than or equal
3608 to the largest element in \c{t1}), the operation will fail and
3611 This operation completes in \cw{O(log N)} time, no matter how large
3612 the trees being joined together.
3614 \S{utils-join234r} \cw{join234r()}
3616 \c tree234 *join234r(tree234 *t1, tree234 *t2);
3618 Joins two trees together in exactly the same way as \cw{join234()},
3619 but this time the combined tree is returned in \c{t2}, and \c{t1} is
3620 destroyed. The elements in \c{t1} still appear before those in
3623 Again, this operation completes in \cw{O(log N)} time, no matter how
3624 large the trees being joined together.
3626 \S{utils-copytree234} \cw{copytree234()}
3628 \c tree234 *copytree234(tree234 *t, copyfn234 copyfn,
3629 \c void *copyfnstate);
3631 Makes a copy of an entire tree.
3633 If \c{copyfn} is \cw{NULL}, the tree will be copied but the elements
3634 will not be; i.e. the new tree will contain pointers to exactly the
3635 same physical elements as the old one.
3637 If you want to copy each actual element during the operation, you
3638 can instead pass a function in \c{copyfn} which makes a copy of each
3639 element. That function has the prototype
3641 \c typedef void *(*copyfn234)(void *state, void *element);
3643 and every time it is called, the \c{state} parameter will be set to
3644 the value you passed in as \c{copyfnstate}.
3646 \H{utils-misc} Miscellaneous utility functions and macros
3648 This section contains all the utility functions which didn't
3649 sensibly fit anywhere else.
3651 \S{utils-truefalse} \cw{TRUE} and \cw{FALSE}
3653 The main Puzzles header file defines the macros \cw{TRUE} and
3654 \cw{FALSE}, which are used throughout the code in place of 1 and 0
3655 (respectively) to indicate that the values are in a boolean context.
3656 For code base consistency, I'd prefer it if submissions of new code
3657 followed this convention as well.
3659 \S{utils-maxmin} \cw{max()} and \cw{min()}
3661 The main Puzzles header file defines the pretty standard macros
3662 \cw{max()} and \cw{min()}, each of which is given two arguments and
3663 returns the one which compares greater or less respectively.
3665 These macros may evaluate their arguments multiple times. Avoid side
3668 \S{utils-pi} \cw{PI}
3670 The main Puzzles header file defines a macro \cw{PI} which expands
3671 to a floating-point constant representing pi.
3673 (I've never understood why ANSI's \cw{<math.h>} doesn't define this.
3676 \S{utils-obfuscate-bitmap} \cw{obfuscate_bitmap()}
3678 \c void obfuscate_bitmap(unsigned char *bmp, int bits, int decode);
3680 This function obscures the contents of a piece of data, by
3681 cryptographic methods. It is useful for games of hidden information
3682 (such as Mines, Guess or Black Box), in which the game ID
3683 theoretically reveals all the information the player is supposed to
3684 be trying to guess. So in order that players should be able to send
3685 game IDs to one another without accidentally spoiling the resulting
3686 game by looking at them, these games obfuscate their game IDs using
3689 Although the obfuscation function is cryptographic, it cannot
3690 properly be called encryption because it has no key. Therefore,
3691 anybody motivated enough can re-implement it, or hack it out of the
3692 Puzzles source, and strip the obfuscation off one of these game IDs
3693 to see what lies beneath. (Indeed, they could usually do it much
3694 more easily than that, by entering the game ID into their own copy
3695 of the puzzle and hitting Solve.) The aim is not to protect against
3696 a determined attacker; the aim is simply to protect people who
3697 wanted to play the game honestly from \e{accidentally} spoiling
3700 The input argument \c{bmp} points at a piece of memory to be
3701 obfuscated. \c{bits} gives the length of the data. Note that that
3702 length is in \e{bits} rather than bytes: if you ask for obfuscation
3703 of a partial number of bytes, then you will get it. Bytes are
3704 considered to be used from the top down: thus, for example, setting
3705 \c{bits} to 10 will cover the whole of \cw{bmp[0]} and the \e{top
3706 two} bits of \cw{bmp[1]}. The remainder of a partially used byte is
3707 undefined (i.e. it may be corrupted by the function).
3709 The parameter \c{decode} is \cw{FALSE} for an encoding operation,
3710 and \cw{TRUE} for a decoding operation. Each is the inverse of the
3711 other. (There's no particular reason you shouldn't obfuscate by
3712 decoding and restore cleartext by encoding, if you really wanted to;
3713 it should still work.)
3715 The input bitmap is processed in place.
3717 \S{utils-bin2hex} \cw{bin2hex()}
3719 \c char *bin2hex(const unsigned char *in, int inlen);
3721 This function takes an input byte array and converts it into an
3722 ASCII string encoding those bytes in (lower-case) hex. It returns a
3723 dynamically allocated string containing that encoding.
3725 This function is useful for encoding the result of
3726 \cw{obfuscate_bitmap()} in printable ASCII for use in game IDs.
3728 \S{utils-hex2bin} \cw{hex2bin()}
3730 \c unsigned char *hex2bin(const char *in, int outlen);
3732 This function takes an ASCII string containing hex digits, and
3733 converts it back into a byte array of length \c{outlen}. If there
3734 aren't enough hex digits in the string, the contents of the
3735 resulting array will be undefined.
3737 This function is the inverse of \cw{bin2hex()}.
3739 \S{utils-game-mkhighlight} \cw{game_mkhighlight()}
3741 \c void game_mkhighlight(frontend *fe, float *ret,
3742 \c int background, int highlight, int lowlight);
3744 It's reasonably common for a puzzle game's graphics to use
3745 highlights and lowlights to indicate \q{raised} or \q{lowered}
3746 sections. Fifteen, Sixteen and Twiddle are good examples of this.
3748 Puzzles using this graphical style are running a risk if they just
3749 use whatever background colour is supplied to them by the front end,
3750 because that background colour might be too light to see any
3751 highlights on at all. (In particular, it's not unheard of for the
3752 front end to specify a default background colour of white.)
3754 Therefore, such puzzles can call this utility function from their
3755 \cw{colours()} routine (\k{backend-colours}). You pass it your front
3756 end handle, a pointer to the start of your return array, and three
3757 colour indices. It will:
3759 \b call \cw{frontend_default_colour()} (\k{frontend-default-colour})
3760 to fetch the front end's default background colour
3762 \b alter the brightness of that colour if it's unsuitable
3764 \b define brighter and darker variants of the colour to be used as
3765 highlights and lowlights
3767 \b write those results into the relevant positions in the \c{ret}
3770 Thus, \cw{ret[background*3]} to \cw{ret[background*3+2]} will be set
3771 to RGB values defining a sensible background colour, and similary
3772 \c{highlight} and \c{lowlight} will be set to sensible colours.
3774 \C{writing} How to write a new puzzle
3776 This chapter gives a guide to how to actually write a new puzzle:
3777 where to start, what to do first, how to solve common problems.
3779 The previous chapters have been largely composed of facts. This one
3782 \H{writing-editorial} Choosing a puzzle
3784 Before you start writing a puzzle, you have to choose one. Your
3785 taste in puzzle games is up to you, of course; and, in fact, you're
3786 probably reading this guide because you've \e{already} thought of a
3787 game you want to write. But if you want to get it accepted into the
3788 official Puzzles distribution, then there's a criterion it has to
3791 The current Puzzles editorial policy is that all games should be
3792 \e{fair}. A fair game is one which a player can only fail to
3793 complete through demonstrable lack of skill \dash that is, such that
3794 a better player in the same situation would have \e{known} to do
3795 something different.
3797 For a start, that means every game presented to the user must have
3798 \e{at least one solution}. Giving the unsuspecting user a puzzle
3799 which is actually impossible is not acceptable. (There is an
3800 exception: if the user has selected some non-default option which is
3801 clearly labelled as potentially unfair, \e{then} you're allowed to
3802 generate possibly insoluble puzzles, because the user isn't
3803 unsuspecting any more. Same Game and Mines both have options of this
3806 Also, this actually \e{rules out} games such as Klondike, or the
3807 normal form of Mahjong Solitaire. Those games have the property that
3808 even if there is a solution (i.e. some sequence of moves which will
3809 get from the start state to the solved state), the player doesn't
3810 necessarily have enough information to \e{find} that solution. In
3811 both games, it is possible to reach a dead end because you had an
3812 arbitrary choice to make and made it the wrong way. This violates
3813 the fairness criterion, because a better player couldn't have known
3814 they needed to make the other choice.
3816 (GNOME has a variant on Mahjong Solitaire which makes it fair: there
3817 is a Shuffle operation which randomly permutes all the remaining
3818 tiles without changing their positions, which allows you to get out
3819 of a sticky situation. Using this operation adds a 60-second penalty
3820 to your solution time, so it's to the player's advantage to try to
3821 minimise the chance of having to use it. It's still possible to
3822 render the game uncompletable if you end up with only two tiles
3823 vertically stacked, but that's easy to foresee and avoid using a
3824 shuffle operation. This form of the game \e{is} fair. Implementing
3825 it in Puzzles would require an infrastructure change so that the
3826 back end could communicate time penalties to the mid-end, but that
3827 would be easy enough.)
3829 Providing a \e{unique} solution is a little more negotiable; it
3830 depends on the puzzle. Solo would have been of unacceptably low
3831 quality if it didn't always have a unique solution, whereas Twiddle
3832 inherently has multiple solutions by its very nature and it would
3833 have been meaningless to even \e{suggest} making it uniquely
3834 soluble. Somewhere in between, Flip could reasonably be made to have
3835 unique solutions (by enforcing a zero-dimension kernel in every
3836 generated matrix) but it doesn't seem like a serious quality problem
3839 Of course, you don't \e{have} to care about all this. There's
3840 nothing stopping you implementing any puzzle you want to if you're
3841 happy to maintain your puzzle yourself, distribute it from your own
3842 web site, fork the Puzzles code completely, or anything like that.
3843 It's free software; you can do what you like with it. But any game
3844 that you want to be accepted into \e{my} Puzzles code base has to
3845 satisfy the fairness criterion, which means all randomly generated
3846 puzzles must have a solution (unless the user has deliberately
3847 chosen otherwise) and it must be possible \e{in theory} to find that
3848 solution without having to guess.
3850 \H{writing-gs} Getting started
3852 The simplest way to start writing a new puzzle is to copy
3853 \c{nullgame.c}. This is a template puzzle source file which does
3854 almost nothing, but which contains all the back end function
3855 prototypes and declares the back end data structure correctly. It is
3856 built every time the rest of Puzzles is built, to ensure that it
3857 doesn't get out of sync with the code and remains buildable.
3859 So start by copying \c{nullgame.c} into your new source file. Then
3860 you'll gradually add functionality until the very boring Null Game
3861 turns into your real game.
3863 Next you'll need to add your puzzle to the Makefiles, in order to
3864 compile it conveniently. \e{Do not edit the Makefiles}: they are
3865 created automatically by the script \c{mkfiles.pl}, from the file
3866 called \c{Recipe}. Edit \c{Recipe}, and then re-run \c{mkfiles.pl}.
3868 Also, don't forget to add your puzzle to \c{list.c}: if you don't,
3869 then it will still run fine on platforms which build each puzzle
3870 separately, but Mac OS X and other monolithic platforms will not
3871 include your new puzzle in their single binary.
3873 Once your source file is building, you can move on to the fun bit.
3875 \S{writing-generation} Puzzle generation
3877 Randomly generating instances of your puzzle is almost certain to be
3878 the most difficult part of the code, and also the task with the
3879 highest chance of turning out to be completely infeasible. Therefore
3880 I strongly recommend doing it \e{first}, so that if it all goes
3881 horribly wrong you haven't wasted any more time than you absolutely
3882 had to. What I usually do is to take an unmodified \c{nullgame.c},
3883 and start adding code to \cw{new_game_desc()} which tries to
3884 generate a puzzle instance and print it out using \cw{printf()}.
3885 Once that's working, \e{then} I start connecting it up to the return
3886 value of \cw{new_game_desc()}, populating other structures like
3887 \c{game_params}, and generally writing the rest of the source file.
3889 There are many ways to generate a puzzle which is known to be
3890 soluble. In this section I list all the methods I currently know of,
3891 in case any of them can be applied to your puzzle. (Not all of these
3892 methods will work, or in some cases even make sense, for all
3895 Some puzzles are mathematically tractable, meaning you can work out
3896 in advance which instances are soluble. Sixteen, for example, has a
3897 parity constraint in some settings which renders exactly half the
3898 game space unreachable, but it can be mathematically proved that any
3899 position not in that half \e{is} reachable. Therefore, Sixteen's
3900 grid generation simply consists of selecting at random from a well
3901 defined subset of the game space. Cube in its default state is even
3902 easier: \e{every} possible arrangement of the blue squares and the
3903 cube's starting position is soluble!
3905 Another option is to redefine what you mean by \q{soluble}. Black
3906 Box takes this approach. There are layouts of balls in the box which
3907 are completely indistinguishable from one another no matter how many
3908 beams you fire into the box from which angles, which would normally
3909 be grounds for declaring those layouts unfair; but fortunately,
3910 detecting that indistinguishability is computationally easy. So
3911 Black Box doesn't demand that your ball placements match its own; it
3912 merely demands that your ball placements be \e{indistinguishable}
3913 from the ones it was thinking of. If you have an ambiguous puzzle,
3914 then any of the possible answers is considered to be a solution.
3915 Having redefined the rules in that way, any puzzle is soluble again.
3917 Those are the simple techniques. If they don't work, you have to get
3920 One way to generate a soluble puzzle is to start from the solved
3921 state and make inverse moves until you reach a starting state. Then
3922 you know there's a solution, because you can just list the inverse
3923 moves you made and make them in the opposite order to return to the
3926 This method can be simple and effective for puzzles where you get to
3927 decide what's a starting state and what's not. In Pegs, for example,
3928 the generator begins with one peg in the centre of the board and
3929 makes inverse moves until it gets bored; in this puzzle, valid
3930 inverse moves are easy to detect, and \e{any} state that's reachable
3931 from the solved state by inverse moves is a reasonable starting
3932 position. So Pegs just continues making inverse moves until the
3933 board satisfies some criteria about extent and density, and then
3934 stops and declares itself done.
3936 For other puzzles, it can be a lot more difficult. Same Game uses
3937 this strategy too, and it's lucky to get away with it at all: valid
3938 inverse moves aren't easy to find (because although it's easy to
3939 insert additional squares in a Same Game position, it's difficult to
3940 arrange that \e{after} the insertion they aren't adjacent to any
3941 other squares of the same colour), so you're constantly at risk of
3942 running out of options and having to backtrack or start again. Also,
3943 Same Game grids never start off half-empty, which means you can't
3944 just stop when you run out of moves \dash you have to find a way to
3945 fill the grid up \e{completely}.
3947 The other way to generate a puzzle that's soluble is to start from
3948 the other end, and actually write a \e{solver}. This tends to ensure
3949 that a puzzle has a \e{unique} solution over and above having a
3950 solution at all, so it's a good technique to apply to puzzles for
3951 which that's important.
3953 One theoretical drawback of generating soluble puzzles by using a
3954 solver is that your puzzles are restricted in difficulty to those
3955 which the solver can handle. (Most solvers are not fully general:
3956 many sets of puzzle rules are NP-complete or otherwise nasty, so
3957 most solvers can only handle a subset of the theoretically soluble
3958 puzzles.) It's been my experience in practice, however, that this
3959 usually isn't a problem; computers are good at very different things
3960 from humans, and what the computer thinks is nice and easy might
3961 still be pleasantly challenging for a human. For example, when
3962 solving Dominosa puzzles I frequently find myself using a variety of
3963 reasoning techniques that my solver doesn't know about; in
3964 principle, therefore, I should be able to solve the puzzle using
3965 only those techniques it \e{does} know about, but this would involve
3966 repeatedly searching the entire grid for the one simple deduction I
3967 can make. Computers are good at this sort of exhaustive search, but
3968 it's been my experience that human solvers prefer to do more complex
3969 deductions than to spend ages searching for simple ones. So in many
3970 cases I don't find my own playing experience to be limited by the
3971 restrictions on the solver.
3973 (This isn't \e{always} the case. Solo is a counter-example;
3974 generating Solo puzzles using a simple solver does lead to
3975 qualitatively easier puzzles. Therefore I had to make the Solo
3976 solver rather more advanced than most of them.)
3978 There are several different ways to apply a solver to the problem of
3979 generating a soluble puzzle. I list a few of them below.
3981 The simplest approach is brute force: randomly generate a puzzle,
3982 use the solver to see if it's soluble, and if not, throw it away and
3983 try again until you get lucky. This is often a viable technique if
3984 all else fails, but it tends not to scale well: for many puzzle
3985 types, the probability of finding a uniquely soluble instance
3986 decreases sharply as puzzle size goes up, so this technique might
3987 work reasonably fast for small puzzles but take (almost) forever at
3988 larger sizes. Still, if there's no other alternative it can be
3989 usable: Pattern and Dominosa both use this technique. (However,
3990 Dominosa has a means of tweaking the randomly generated grids to
3991 increase the \e{probability} of them being soluble, by ruling out
3992 one of the most common ambiguous cases. This improved generation
3993 speed by over a factor of 10 on the highest preset!)
3995 An approach which can be more scalable involves generating a grid
3996 and then tweaking it to make it soluble. This is the technique used
3997 by Mines and also by Net: first a random puzzle is generated, and
3998 then the solver is run to see how far it gets. Sometimes the solver
3999 will get stuck; when that happens, examine the area it's having
4000 trouble with, and make a small random change in that area to allow
4001 it to make more progress. Continue solving (possibly even without
4002 restarting the solver), tweaking as necessary, until the solver
4003 finishes. Then restart the solver from the beginning to ensure that
4004 the tweaks haven't caused new problems in the process of solving old
4005 ones (which can sometimes happen).
4007 This strategy works well in situations where the usual solver
4008 failure mode is to get stuck in an easily localised spot. Thus it
4009 works well for Net and Mines, whose most common failure mode tends
4010 to be that most of the grid is fine but there are a few widely
4011 separated ambiguous sections; but it would work less well for
4012 Dominosa, in which the way you get stuck is to have scoured the
4013 whole grid and not found anything you can deduce \e{anywhere}. Also,
4014 it relies on there being a low probability that tweaking the grid
4015 introduces a new problem at the same time as solving the old one;
4016 Mines and Net also have the property that most of their deductions
4017 are local, so that it's very unlikely for a tweak to affect
4018 something half way across the grid from the location where it was
4019 applied. In Dominosa, by contrast, a lot of deductions use
4020 information about half the grid (\q{out of all the sixes, only one
4021 is next to a three}, which can depend on the values of up to 32 of
4022 the 56 squares in the default setting!), so this tweaking strategy
4023 would be rather less likely to work well.
4025 A more specialised strategy is that used in Solo and Slant. These
4026 puzzles have the property that they derive their difficulty from not
4027 presenting all the available clues. (In Solo's case, if all the
4028 possible clues were provided then the puzzle would already be
4029 solved; in Slant it would still require user action to fill in the
4030 lines, but it would present no challenge at all). Therefore, a
4031 simple generation technique is to leave the decision of which clues
4032 to provide until the last minute. In other words, first generate a
4033 random \e{filled} grid with all possible clues present, and then
4034 gradually remove clues for as long as the solver reports that it's
4035 still soluble. Unlike the methods described above, this technique
4036 \e{cannot} fail \dash once you've got a filled grid, nothing can
4037 stop you from being able to convert it into a viable puzzle.
4038 However, it wouldn't even be meaningful to apply this technique to
4039 (say) Pattern, in which clues can never be left out, so the only way
4040 to affect the set of clues is by altering the solution.
4042 (Unfortunately, Solo is complicated by the need to provide puzzles
4043 at varying difficulty levels. It's easy enough to generate a puzzle
4044 of \e{at most} a given level of difficulty; you just have a solver
4045 with configurable intelligence, and you set it to a given level and
4046 apply the above technique, thus guaranteeing that the resulting grid
4047 is solvable by someone with at most that much intelligence. However,
4048 generating a puzzle of \e{at least} a given level of difficulty is
4049 rather harder; if you go for \e{at most} Intermediate level, you're
4050 likely to find that you've accidentally generated a Trivial grid a
4051 lot of the time, because removing just one number is sufficient to
4052 take the puzzle from Trivial straight to Ambiguous. In that
4053 situation Solo has no remaining options but to throw the puzzle away
4056 A final strategy is to use the solver \e{during} puzzle
4057 construction: lay out a bit of the grid, run the solver to see what
4058 it allows you to deduce, and then lay out a bit more to allow the
4059 solver to make more progress. There are articles on the web that
4060 recommend constructing Sudoku puzzles by this method (which is
4061 completely the opposite way round to how Solo does it); for Sudoku
4062 it has the advantage that you get to specify your clue squares in
4063 advance (so you can have them make pretty patterns).
4065 Rectangles uses a strategy along these lines. First it generates a
4066 grid by placing the actual rectangles; then it has to decide where
4067 in each rectangle to place a number. It uses a solver to help it
4068 place the numbers in such a way as to ensure a unique solution. It
4069 does this by means of running a test solver, but it runs the solver
4070 \e{before} it's placed any of the numbers \dash which means the
4071 solver must be capable of coping with uncertainty about exactly
4072 where the numbers are! It runs the solver as far as it can until it
4073 gets stuck; then it narrows down the possible positions of a number
4074 in order to allow the solver to make more progress, and so on. Most
4075 of the time this process terminates with the grid fully solved, at
4076 which point any remaining number-placement decisions can be made at
4077 random from the options not so far ruled out. Note that unlike the
4078 Net/Mines tweaking strategy described above, this algorithm does not
4079 require a checking run after it completes: if it finishes
4080 successfully at all, then it has definitely produced a uniquely
4083 Most of the strategies described above are not 100% reliable. Each
4084 one has a failure rate: every so often it has to throw out the whole
4085 grid and generate a fresh one from scratch. (Solo's strategy would
4086 be the exception, if it weren't for the need to provide configurable
4087 difficulty levels.) Occasional failures are not a fundamental
4088 problem in this sort of work, however: it's just a question of
4089 dividing the grid generation time by the success rate (if it takes
4090 10ms to generate a candidate grid and 1/5 of them work, then it will
4091 take 50ms on average to generate a viable one), and seeing whether
4092 the expected time taken to \e{successfully} generate a puzzle is
4093 unacceptably slow. Dominosa's generator has a very low success rate
4094 (about 1 out of 20 candidate grids turn out to be usable, and if you
4095 think \e{that's} bad then go and look at the source code and find
4096 the comment showing what the figures were before the generation-time
4097 tweaks!), but the generator itself is very fast so this doesn't
4098 matter. Rectangles has a slower generator, but fails well under 50%
4101 So don't be discouraged if you have an algorithm that doesn't always
4102 work: if it \e{nearly} always works, that's probably good enough.
4103 The one place where reliability is important is that your algorithm
4104 must never produce false positives: it must not claim a puzzle is
4105 soluble when it isn't. It can produce false negatives (failing to
4106 notice that a puzzle is soluble), and it can fail to generate a
4107 puzzle at all, provided it doesn't do either so often as to become
4110 One last piece of advice: for grid-based puzzles, when writing and
4111 testing your generation algorithm, it's almost always a good idea
4112 \e{not} to test it initially on a grid that's square (i.e.
4113 \cw{w==h}), because if the grid is square then you won't notice if
4114 you mistakenly write \c{h} instead of \c{w} (or vice versa)
4115 somewhere in the code. Use a rectangular grid for testing, and any
4116 size of grid will be likely to work after that.
4118 \S{writing-textformats} Designing textual description formats
4120 Another aspect of writing a puzzle which is worth putting some
4121 thought into is the design of the various text description formats:
4122 the format of the game parameter encoding, the game description
4123 encoding, and the move encoding.
4125 The first two of these should be reasonably intuitive for a user to
4126 type in; so provide some flexibility where possible. Suppose, for
4127 example, your parameter format consists of two numbers separated by
4128 an \c{x} to specify the grid dimensions (\c{10x10} or \c{20x15}),
4129 and then has some suffixes to specify other aspects of the game
4130 type. It's almost always a good idea in this situation to arrange
4131 that \cw{decode_params()} can handle the suffixes appearing in any
4132 order, even if \cw{encode_params()} only ever generates them in one
4135 These formats will also be expected to be reasonably stable: users
4136 will expect to be able to exchange game IDs with other users who
4137 aren't running exactly the same version of your game. So make them
4138 robust and stable: don't build too many assumptions into the game ID
4139 format which will have to be changed every time something subtle
4140 changes in the puzzle code.
4142 \H{writing-howto} Common how-to questions
4144 This section lists some common things people want to do when writing
4145 a puzzle, and describes how to achieve them within the Puzzles
4148 \S{writing-howto-cursor} Drawing objects at only one position
4150 A common phenomenon is to have an object described in the
4151 \c{game_state} or the \c{game_ui} which can only be at one position.
4152 A cursor \dash probably specified in the \c{game_ui} \dash is a good
4155 In the \c{game_ui}, it would \e{obviously} be silly to have an array
4156 covering the whole game grid with a boolean flag stating whether the
4157 cursor was at each position. Doing that would waste space, would
4158 make it difficult to find the cursor in order to do anything with
4159 it, and would introduce the potential for synchronisation bugs in
4160 which you ended up with two cursors or none. The obviously sensible
4161 way to store a cursor in the \c{game_ui} is to have fields directly
4162 encoding the cursor's coordinates.
4164 However, it is a mistake to assume that the same logic applies to
4165 the \c{game_drawstate}. If you replicate the cursor position fields
4166 in the draw state, the redraw code will get very complicated. In the
4167 draw state, in fact, it \e{is} probably the right thing to have a
4168 cursor flag for every position in the grid. You probably have an
4169 array for the whole grid in the drawstate already (stating what is
4170 currently displayed in the window at each position); the sensible
4171 approach is to add a \q{cursor} flag to each element of that array.
4172 Then the main redraw loop will look something like this
4175 \c for (y = 0; y < h; y++) {
4176 \c for (x = 0; x < w; x++) {
4177 \c int value = state->symbol_at_position[y][x];
4178 \c if (x == ui->cursor_x && y == ui->cursor_y)
4180 \c if (ds->symbol_at_position[y][x] != value) {
4181 \c symbol_drawing_subroutine(dr, ds, x, y, value);
4182 \c ds->symbol_at_position[y][x] = value;
4187 This loop is very simple, pretty hard to get wrong, and
4188 \e{automatically} deals both with erasing the previous cursor and
4189 drawing the new one, with no special case code required.
4191 This type of loop is generally a sensible way to write a redraw
4192 function, in fact. The best thing is to ensure that the information
4193 stored in the draw state for each position tells you \e{everything}
4194 about what was drawn there. A good way to ensure that is to pass
4195 precisely the same information, and \e{only} that information, to a
4196 subroutine that does the actual drawing; then you know there's no
4197 additional information which affects the drawing but which you don't
4200 \S{writing-keyboard-cursor} Implementing a keyboard-controlled cursor
4202 It is often useful to provide a keyboard control method in a
4203 basically mouse-controlled game. A keyboard-controlled cursor is
4204 best implemented by storing its location in the \c{game_ui} (since
4205 if it were in the \c{game_state} then the user would have to
4206 separately undo every cursor move operation). So the procedure would
4209 \b Put cursor position fields in the \c{game_ui}.
4211 \b \cw{interpret_move()} responds to arrow keys by modifying the
4212 cursor position fields and returning \cw{""}.
4214 \b \cw{interpret_move()} responds to some sort of fire button by
4215 actually performing a move based on the current cursor location.
4217 \b You might want an additional \c{game_ui} field stating whether
4218 the cursor is currently visible, and having it disappear when a
4219 mouse action occurs (so that it doesn't clutter the display when not
4222 \b You might also want to automatically hide the cursor in
4223 \cw{changed_state()} when the current game state changes to one in
4224 which there is no move to make (which is the case in some types of
4227 \b \cw{redraw()} draws the cursor using the technique described in
4228 \k{writing-howto-cursor}.
4230 \S{writing-howto-dragging} Implementing draggable sprites
4232 Some games have a user interface which involves dragging some sort
4233 of game element around using the mouse. If you need to show a
4234 graphic moving smoothly over the top of other graphics, use a
4235 blitter (see \k{drawing-blitter} for the blitter API) to save the
4236 background underneath it. The typical scenario goes:
4238 \b Have a blitter field in the \c{game_drawstate}.
4240 \b Set the blitter field to \cw{NULL} in the game's
4241 \cw{new_drawstate()} function, since you don't yet know how big the
4242 piece of saved background needs to be.
4244 \b In the game's \cw{set_size()} function, once you know the size of
4245 the object you'll be dragging around the display and hence the
4246 required size of the blitter, actually allocate the blitter.
4248 \b In \cw{free_drawstate()}, free the blitter if it's not \cw{NULL}.
4250 \b In \cw{interpret_move()}, respond to mouse-down and mouse-drag
4251 events by updating some fields in the \cw{game_ui} which indicate
4252 that a drag is in progress.
4254 \b At the \e{very end} of \cw{redraw()}, after all other drawing has
4255 been done, draw the moving object if there is one. First save the
4256 background under the object in the blitter; then set a clip
4257 rectangle covering precisely the area you just saved (just in case
4258 anti-aliasing or some other error causes your drawing to go beyond
4259 the area you saved). Then draw the object, and call \cw{unclip()}.
4260 Finally, set a flag in the \cw{game_drawstate} that indicates that
4261 the blitter needs restoring.
4263 \b At the very start of \cw{redraw()}, before doing anything else at
4264 all, check the flag in the \cw{game_drawstate}, and if it says the
4265 blitter needs restoring then restore it. (Then clear the flag, so
4266 that this won't happen again in the next redraw if no moving object
4267 is drawn this time.)
4269 This way, you will be able to write the rest of the redraw function
4270 completely ignoring the dragged object, as if it were floating above
4271 your bitmap and being completely separate.
4273 \S{writing-ref-counting} Sharing large invariant data between all
4276 In some puzzles, there is a large amount of data which never changes
4277 between game states. The array of numbers in Dominosa is a good
4280 You \e{could} dynamically allocate a copy of that array in every
4281 \c{game_state}, and have \cw{dup_game()} make a fresh copy of it for
4282 every new \c{game_state}; but it would waste memory and time. A
4283 more efficient way is to use a reference-counted structure.
4285 \b Define a structure type containing the data in question, and also
4286 containing an integer reference count.
4288 \b Have a field in \c{game_state} which is a pointer to this
4291 \b In \cw{new_game()}, when creating a fresh game state at the start
4292 of a new game, create an instance of this structure, initialise it
4293 with the invariant data, and set its reference count to 1.
4295 \b In \cw{dup_game()}, rather than making a copy of the structure
4296 for the new game state, simply set the new game state to point at
4297 the same copy of the structure, and increment its reference count.
4299 \b In \cw{free_game()}, decrement the reference count in the
4300 structure pointed to by the game state; if the count reaches zero,
4303 This way, the invariant data will persist for only as long as it's
4304 genuinely needed; \e{as soon} as the last game state for a
4305 particular puzzle instance is freed, the invariant data for that
4306 puzzle will vanish as well. Reference counting is a very efficient
4307 form of garbage collection, when it works at all. (Which it does in
4308 this instance, of course, because there's no possibility of circular
4311 \S{writing-flash-types} Implementing multiple types of flash
4313 In some games you need to flash in more than one different way.
4314 Mines, for example, flashes white when you win, and flashes red when
4315 you tread on a mine and die.
4317 The simple way to do this is:
4319 \b Have a field in the \c{game_ui} which describes the type of flash.
4321 \b In \cw{flash_length()}, examine the old and new game states to
4322 decide whether a flash is required and what type. Write the type of
4323 flash to the \c{game_ui} field whenever you return non-zero.
4325 \b In \cw{redraw()}, when you detect that \c{flash_time} is
4326 non-zero, examine the field in \c{game_ui} to decide which type of
4329 \cw{redraw()} will never be called with \c{flash_time} non-zero
4330 unless \cw{flash_length()} was first called to tell the mid-end that
4331 a flash was required; so whenever \cw{redraw()} notices that
4332 \c{flash_time} is non-zero, you can be sure that the field in
4333 \c{game_ui} is correctly set.
4335 \S{writing-move-anim} Animating game moves
4337 A number of puzzle types benefit from a quick animation of each move
4340 For some games, such as Fifteen, this is particularly easy. Whenever
4341 \cw{redraw()} is called with \c{oldstate} non-\cw{NULL}, Fifteen
4342 simply compares the position of each tile in the two game states,
4343 and if the tile is not in the same place then it draws it some
4344 fraction of the way from its old position to its new position. This
4345 method copes automatically with undo.
4347 Other games are less obvious. In Sixteen, for example, you can't
4348 just draw each tile a fraction of the way from its old to its new
4349 position: if you did that, the end tile would zip very rapidly past
4350 all the others to get to the other end and that would look silly.
4351 (Worse, it would look inconsistent if the end tile was drawn on top
4352 going one way and on the bottom going the other way.)
4354 A useful trick here is to define a field or two in the game state
4355 that indicates what the last move was.
4357 \b Add a \q{last move} field to the \c{game_state} (or two or more
4358 fields if the move is complex enough to need them).
4360 \b \cw{new_game()} initialises this field to a null value for a new
4363 \b \cw{execute_move()} sets up the field to reflect the move it just
4366 \b \cw{redraw()} now needs to examine its \c{dir} parameter. If
4367 \c{dir} is positive, it determines the move being animated by
4368 looking at the last-move field in \c{newstate}; but if \c{dir} is
4369 negative, it has to look at the last-move field in \c{oldstate}, and
4370 invert whatever move it finds there.
4372 Note also that Sixteen needs to store the \e{direction} of the move,
4373 because you can't quite determine it by examining the row or column
4374 in question. You can in almost all cases, but when the row is
4375 precisely two squares long it doesn't work since a move in either
4376 direction looks the same. (You could argue that since moving a
4377 2-element row left and right has the same effect, it doesn't matter
4378 which one you animate; but in fact it's very disorienting to click
4379 the arrow left and find the row moving right, and almost as bad to
4380 undo a move to the right and find the game animating \e{another}
4383 \S{writing-conditional-anim} Animating drag operations
4385 In Untangle, moves are made by dragging a node from an old position
4386 to a new position. Therefore, at the time when the move is initially
4387 made, it should not be animated, because the node has already been
4388 dragged to the right place and doesn't need moving there. However,
4389 it's nice to animate the same move if it's later undone or redone.
4390 This requires a bit of fiddling.
4392 The obvious approach is to have a flag in the \c{game_ui} which
4393 inhibits move animation, and to set that flag in
4394 \cw{interpret_move()}. The question is, when would the flag be reset
4395 again? The obvious place to do so is \cw{changed_state()}, which
4396 will be called once per move. But it will be called \e{before}
4397 \cw{anim_length()}, so if it resets the flag then \cw{anim_length()}
4398 will never see the flag set at all.
4400 The solution is to have \e{two} flags in a queue.
4402 \b Define two flags in \c{game_ui}; let's call them \q{current} and
4405 \b Set both to \cw{FALSE} in \c{new_ui()}.
4407 \b When a drag operation completes in \cw{interpret_move()}, set the
4408 \q{next} flag to \cw{TRUE}.
4410 \b Every time \cw{changed_state()} is called, set the value of
4411 \q{current} to the value in \q{next}, and then set the value of
4412 \q{next} to \cw{FALSE}.
4414 \b That way, \q{current} will be \cw{TRUE} \e{after} a call to
4415 \cw{changed_state()} if and only if that call to
4416 \cw{changed_state()} was the result of a drag operation processed by
4417 \cw{interpret_move()}. Any other call to \cw{changed_state()}, due
4418 to an Undo or a Redo or a Restart or a Solve, will leave \q{current}
4421 \b So now \cw{anim_length()} can request a move animation if and
4422 only if the \q{current} flag is \e{not} set.
4424 \S{writing-cheating} Inhibiting the victory flash when Solve is used
4426 Many games flash when you complete them, as a visual congratulation
4427 for having got to the end of the puzzle. It often seems like a good
4428 idea to disable that flash when the puzzle is brought to a solved
4429 state by means of the Solve operation.
4431 This is easily done:
4433 \b Add a \q{cheated} flag to the \c{game_state}.
4435 \b Set this flag to \cw{FALSE} in \cw{new_game()}.
4437 \b Have \cw{solve()} return a move description string which clearly
4438 identifies the move as a solve operation.
4440 \b Have \cw{execute_move()} respond to that clear identification by
4441 setting the \q{cheated} flag in the returned \c{game_state}. The
4442 flag will then be propagated to all subsequent game states, even if
4443 the user continues fiddling with the game after it is solved.
4445 \b \cw{flash_length()} now returns non-zero if \c{oldstate} is not
4446 completed and \c{newstate} is, \e{and} neither state has the
4447 \q{cheated} flag set.
4449 \H{writing-testing} Things to test once your puzzle is written
4451 Puzzle implementations written in this framework are self-testing as
4452 far as I could make them.
4454 Textual game and move descriptions, for example, are generated and
4455 parsed as part of the normal process of play. Therefore, if you can
4456 make moves in the game \e{at all} you can be reasonably confident
4457 that the mid-end serialisation interface will function correctly and
4458 you will be able to save your game. (By contrast, if I'd stuck with
4459 a single \cw{make_move()} function performing the jobs of both
4460 \cw{interpret_move()} and \cw{execute_move()}, and had separate
4461 functions to encode and decode a game state in string form, then
4462 those functions would not be used during normal play; so they could
4463 have been completely broken, and you'd never know it until you tried
4464 to save the game \dash which would have meant you'd have to test
4465 game saving \e{extensively} and make sure to test every possible
4466 type of game state. As an added bonus, doing it the way I did leads
4467 to smaller save files.)
4469 There is one exception to this, which is the string encoding of the
4470 \c{game_ui}. Most games do not store anything permanent in the
4471 \c{game_ui}, and hence do not need to put anything in its encode and
4472 decode functions; but if there is anything in there, you do need to
4473 test game loading and saving to ensure those functions work
4476 It's also worth testing undo and redo of all operations, to ensure
4477 that the redraw and the animations (if any) work properly. Failing
4478 to animate undo properly seems to be a common error.
4480 Other than that, just use your common sense.