loopy.c

   1 /*
   2  * loopy.c: An implementation of the Nikoli game 'Loop the loop'.
   3  * (c) Mike Pinna, 2005
   4  *
   5  * vim: set shiftwidth=4 :set textwidth=80:
   6  */
   7
   8 /*
   9  * TODO:
  10  *
  11  *  - setting very high recursion depth seems to cause memory
  12  *    munching: are we recursing before checking completion, by any
  13  *    chance?
  14  *
  15  *  - there's an interesting deductive technique which makes use of
  16  *    topology rather than just graph theory. Each _square_ in the
  17  *    grid is either inside or outside the loop; you can tell that
  18  *    two squares are on the same side of the loop if they're
  19  *    separated by an x (or, more generally, by a path crossing no
  20  *    LINE_UNKNOWNs and an even number of LINE_YESes), and on the
  21  *    opposite side of the loop if they're separated by a line (or
  22  *    an odd number of LINE_YESes and no LINE_UNKNOWNs). Oh, and
  23  *    any square separated from the outside of the grid by a
  24  *    LINE_YES or a LINE_NO is on the inside or outside
  25  *    respectively. So if you can track this for all squares, you
  26  *    can occasionally spot that two squares are separated by a
  27  *    LINE_UNKNOWN but their relative insideness is known, and
  28  *    therefore deduce the state of the edge between them.
  29  *     + An efficient way to track this would be by augmenting the
  30  *       disjoint set forest data structure. Each element, along
  31  *       with a pointer to a parent member of its equivalence
  32  *       class, would also carry a one-bit field indicating whether
  33  *       it was equal or opposite to its parent. Then you could
  34  *       keep flipping a bit as you ascended the tree during
  35  *       dsf_canonify(), and hence you'd be able to return the
  36  *       relationship of the input value to its ultimate parent
  37  *       (and also you could then get all those bits right when you
  38  *       went back up the tree rewriting). So you'd be able to
  39  *       query whether any two elements were known-equal,
  40  *       known-opposite, or not-known, and you could add new
  41  *       equalities or oppositenesses to increase your knowledge.
  42  *       (Of course the algorithm would have to fail an assertion
  43  *       if you tried to tell it two things it already knew to be
  44  *       opposite were equal, or vice versa!)
  45  *       This data structure would also be useful in the
  46  *       graph-theoretic part of the solver, where it could be used
  47  *       for storing information about which lines are known-identical
  48  *       or known-opposite.  (For example if two lines bordering a 3
  49  *       are known-identical they must both be LINE_YES, and if they
  50  *       are known-opposite, the *other* two lines bordering that clue
  51  *       must be LINE_YES, etc).  This may duplicate some
  52  *       functionality already present in the solver but it is more
  53  *       general and we could remove the old code, so that's no bad
  54  *       thing.
  55  */
  56
  57 #include <stdio.h>
  58 #include <stdlib.h>
  59 #include <string.h>
  60 #include <assert.h>
  61 #include <ctype.h>
  62 #include <math.h>
  63
  64 #include "puzzles.h"
  65 #include "tree234.h"
  66
  67 #define PREFERRED_TILE_SIZE 32
  68 #define TILE_SIZE (ds->tilesize)
  69 #define LINEWIDTH (ds->linewidth)
  70 #define BORDER (TILE_SIZE / 2)
  71
  72 #define FLASH_TIME 0.5F
  73
  74 #define HL_COUNT(state) ((state)->w * ((state)->h + 1))
  75 #define VL_COUNT(state) (((state)->w + 1) * (state)->h)
  76 #define DOT_COUNT(state) (((state)->w + 1) * ((state)->h + 1))
  77 #define SQUARE_COUNT(state) ((state)->w * (state)->h)
  78
  79 #define ABOVE_SQUARE(state, i, j) ((state)->hl[(i) + (state)->w * (j)])
  80 #define BELOW_SQUARE(state, i, j) ABOVE_SQUARE(state, i, (j)+1)
  81
  82 #define LEFTOF_SQUARE(state, i, j)  ((state)->vl[(i) + ((state)->w + 1) * (j)])
  83 #define RIGHTOF_SQUARE(state, i, j) LEFTOF_SQUARE(state, (i)+1, j)
  84
  85 #define LEGAL_DOT(state, i, j) ((i) >= 0 && (j) >= 0 &&                 \
  86                                 (i) <= (state)->w && (j) <= (state)->h)
  87
  88 /*
  89  * These macros return rvalues only, but can cope with being passed
  90  * out-of-range coordinates.
  91  */
  92 #define ABOVE_DOT(state, i, j) ((!LEGAL_DOT(state, i, j) || j <= 0) ?  \
  93                                 LINE_NO : LV_ABOVE_DOT(state, i, j))
  94 #define BELOW_DOT(state, i, j) ((!LEGAL_DOT(state, i, j) || j >= (state)->h) ? \
  95                                 LINE_NO : LV_BELOW_DOT(state, i, j))
  96
  97 #define LEFTOF_DOT(state, i, j)  ((!LEGAL_DOT(state, i, j) || i <= 0) ? \
  98                                   LINE_NO : LV_LEFTOF_DOT(state, i, j))
  99 #define RIGHTOF_DOT(state, i, j) ((!LEGAL_DOT(state, i, j) || i >= (state)->w)?\
 100                                   LINE_NO : LV_RIGHTOF_DOT(state, i, j))
 101
 102 /*
 103  * These macros expect to be passed valid coordinates, and return
 104  * lvalues.
 105  */
 106 #define LV_BELOW_DOT(state, i, j) ((state)->vl[(i) + ((state)->w + 1) * (j)])
 107 #define LV_ABOVE_DOT(state, i, j) LV_BELOW_DOT(state, i, (j)-1)
 108
 109 #define LV_RIGHTOF_DOT(state, i, j) ((state)->hl[(i) + (state)->w * (j)])
 110 #define LV_LEFTOF_DOT(state, i, j)  LV_RIGHTOF_DOT(state, (i)-1, j)
 111
 112 #define CLUE_AT(state, i, j) ((i < 0 || i >= (state)->w || \
 113                                j < 0 || j >= (state)->h) ? \
 114                              ' ' : LV_CLUE_AT(state, i, j))
 115
 116 #define LV_CLUE_AT(state, i, j) ((state)->clues[(i) + (state)->w * (j)])
 117
 118 #define OPP(dir) (dir == LINE_UNKNOWN ? LINE_UNKNOWN : \
 119                   dir == LINE_YES ? LINE_NO : LINE_YES)
 120
 121 #define BIT_SET(field, bit) ((field) & (1<<(bit)))
 122
 123 #define SET_BIT(field, bit)  (BIT_SET(field, bit) ? FALSE : \
 124                               ((field) |= (1<<(bit)), TRUE))
 125
 126 #define CLEAR_BIT(field, bit) (BIT_SET(field, bit) ?        \
 127                                ((field) &= ~(1<<(bit)), TRUE) : FALSE)
 128
 129 static char *game_text_format(game_state *state);
 130
 131 enum {
 132     COL_BACKGROUND,
 133     COL_FOREGROUND,
 134     COL_HIGHLIGHT,
 135     COL_MISTAKE,
 136     NCOLOURS
 137 };
 138
 139 /*
 140  * Difficulty levels. I do some macro ickery here to ensure that my
 141  * enum and the various forms of my name list always match up.
 142  */
 143 #define DIFFLIST(A) \
 144     A(EASY,Easy,e) \
 145     A(NORMAL,Normal,n)
 146 #define ENUM(upper,title,lower) DIFF_ ## upper,
 147 #define TITLE(upper,title,lower) #title,
 148 #define ENCODE(upper,title,lower) #lower
 149 #define CONFIG(upper,title,lower) ":" #title
 150 enum { DIFFLIST(ENUM) DIFFCOUNT };
 151 /* static char const *const loopy_diffnames[] = { DIFFLIST(TITLE) }; */
 152 static char const loopy_diffchars[] = DIFFLIST(ENCODE);
 153 #define DIFFCONFIG DIFFLIST(CONFIG)
 154
 155 /* LINE_YES_ERROR is only used in the drawing routine */
 156 enum line_state { LINE_UNKNOWN, LINE_YES, LINE_NO /*, LINE_YES_ERROR*/ };
 157
 158 enum direction { UP, DOWN, LEFT, RIGHT };
 159
 160 struct game_params {
 161     int w, h, diff, rec;
 162 };
 163
 164 struct game_state {
 165     int w, h;
 166
 167     /* Put ' ' in a square that doesn't get a clue */
 168     char *clues;
 169
 170     /* Arrays of line states, stored left-to-right, top-to-bottom */
 171     char *hl, *vl;
 172
 173     int solved;
 174     int cheated;
 175
 176     int recursion_depth;
 177 };
 178
 179 static game_state *dup_game(game_state *state)
 180 {
 181     game_state *ret = snew(game_state);
 182
 183     ret->h = state->h;
 184     ret->w = state->w;
 185     ret->solved = state->solved;
 186     ret->cheated = state->cheated;
 187
 188     ret->clues   = snewn(SQUARE_COUNT(state), char);
 189     memcpy(ret->clues, state->clues, SQUARE_COUNT(state));
 190
 191     ret->hl      = snewn(HL_COUNT(state), char);
 192     memcpy(ret->hl, state->hl, HL_COUNT(state));
 193
 194     ret->vl      = snewn(VL_COUNT(state), char);
 195     memcpy(ret->vl, state->vl, VL_COUNT(state));
 196
 197     ret->recursion_depth = state->recursion_depth;
 198
 199     return ret;
 200 }
 201
 202 static void free_game(game_state *state)
 203 {
 204     if (state) {
 205         sfree(state->clues);
 206         sfree(state->hl);
 207         sfree(state->vl);
 208         sfree(state);
 209     }
 210 }
 211
 212 enum solver_status {
 213     SOLVER_SOLVED,    /* This is the only solution the solver could find */
 214     SOLVER_MISTAKE,   /* This is definitely not a solution */
 215     SOLVER_AMBIGUOUS, /* This _might_ be an ambiguous solution */
 216     SOLVER_INCOMPLETE /* This may be a partial solution */
 217 };
 218
 219 typedef struct solver_state {
 220   game_state *state;
 221   char *dot_atleastone;
 222   char *dot_atmostone;
 223 /*   char *dline_identical; */
 224   int recursion_remaining;
 225   enum solver_status solver_status;
 226   /* NB looplen is the number of dots that are joined together at a point, ie a
 227    * looplen of 1 means there are no lines to a particular dot */
 228   int *dotdsf, *looplen;
 229 } solver_state;
 230
 231 static solver_state *new_solver_state(game_state *state) {
 232     solver_state *ret = snew(solver_state);
 233     int i;
 234
 235     ret->state = dup_game(state);
 236
 237     ret->dot_atmostone = snewn(DOT_COUNT(state), char);
 238     memset(ret->dot_atmostone, 0, DOT_COUNT(state));
 239     ret->dot_atleastone = snewn(DOT_COUNT(state), char);
 240     memset(ret->dot_atleastone, 0, DOT_COUNT(state));
 241
 242 #if 0
 243     dline_identical = snewn(DOT_COUNT(state), char);
 244     memset(dline_identical, 0, DOT_COUNT(state));
 245 #endif
 246
 247     ret->recursion_remaining = state->recursion_depth;
 248     ret->solver_status = SOLVER_INCOMPLETE;
 249
 250     ret->dotdsf = snewn(DOT_COUNT(state), int);
 251     ret->looplen = snewn(DOT_COUNT(state), int);
 252     for (i = 0; i < DOT_COUNT(state); i++) {
 253         ret->dotdsf[i] = i;
 254         ret->looplen[i] = 1;
 255     }
 256
 257     return ret;
 258 }
 259
 260 static void free_solver_state(solver_state *sstate) {
 261     if (sstate) {
 262         free_game(sstate->state);
 263         sfree(sstate->dot_atleastone);
 264         sfree(sstate->dot_atmostone);
 265         /*    sfree(sstate->dline_identical); */
 266         sfree(sstate->dotdsf);
 267         sfree(sstate->looplen);
 268         sfree(sstate);
 269     }
 270 }
 271
 272 static solver_state *dup_solver_state(solver_state *sstate) {
 273     game_state *state;
 274
 275     solver_state *ret = snew(solver_state);
 276
 277     ret->state = state = dup_game(sstate->state);
 278
 279     ret->dot_atmostone = snewn(DOT_COUNT(state), char);
 280     memcpy(ret->dot_atmostone, sstate->dot_atmostone, DOT_COUNT(state));
 281
 282     ret->dot_atleastone = snewn(DOT_COUNT(state), char);
 283     memcpy(ret->dot_atleastone, sstate->dot_atleastone, DOT_COUNT(state));
 284
 285 #if 0
 286     ret->dline_identical = snewn((state->w + 1) * (state->h + 1), char);
 287     memcpy(ret->dline_identical, state->dot_atmostone,
 288            (state->w + 1) * (state->h + 1));
 289 #endif
 290
 291     ret->recursion_remaining = sstate->recursion_remaining;
 292     ret->solver_status = sstate->solver_status;
 293
 294     ret->dotdsf = snewn(DOT_COUNT(state), int);
 295     ret->looplen = snewn(DOT_COUNT(state), int);
 296     memcpy(ret->dotdsf, sstate->dotdsf, DOT_COUNT(state) * sizeof(int));
 297     memcpy(ret->looplen, sstate->looplen, DOT_COUNT(state) * sizeof(int));
 298
 299     return ret;
 300 }
 301
 302 /*
 303  * Merge two dots due to the existence of an edge between them.
 304  * Updates the dsf tracking equivalence classes, and keeps track of
 305  * the length of path each dot is currently a part of.
 306  * Returns TRUE if the dots were already linked, ie if they are part of a
 307  * closed loop, and false otherwise.
 308  */
 309 static int merge_dots(solver_state *sstate, int x1, int y1, int x2, int y2)
 310 {
 311     int i, j, len;
 312
 313     i = y1 * (sstate->state->w + 1) + x1;
 314     j = y2 * (sstate->state->w + 1) + x2;
 315
 316     i = dsf_canonify(sstate->dotdsf, i);
 317     j = dsf_canonify(sstate->dotdsf, j);
 318
 319     if (i == j) {
 320         return TRUE;
 321     } else {
 322         len = sstate->looplen[i] + sstate->looplen[j];
 323         dsf_merge(sstate->dotdsf, i, j);
 324         i = dsf_canonify(sstate->dotdsf, i);
 325         sstate->looplen[i] = len;
 326         return FALSE;
 327     }
 328 }
 329
 330 /* Count the number of lines of a particular type currently going into the
 331  * given dot.  Lines going off the edge of the board are assumed fixed no. */
 332 static int dot_order(const game_state* state, int i, int j, char line_type)
 333 {
 334     int n = 0;
 335
 336     if (i > 0) {
 337         if (LEFTOF_DOT(state, i, j) == line_type)
 338             ++n;
 339     } else {
 340         if (line_type == LINE_NO)
 341             ++n;
 342     }
 343     if (i < state->w) {
 344         if (RIGHTOF_DOT(state, i, j) == line_type)
 345             ++n;
 346     } else {
 347         if (line_type == LINE_NO)
 348             ++n;
 349     }
 350     if (j > 0) {
 351         if (ABOVE_DOT(state, i, j) == line_type)
 352             ++n;
 353     } else {
 354         if (line_type == LINE_NO)
 355             ++n;
 356     }
 357     if (j < state->h) {
 358         if (BELOW_DOT(state, i, j) == line_type)
 359             ++n;
 360     } else {
 361         if (line_type == LINE_NO)
 362             ++n;
 363     }
 364
 365     return n;
 366 }
 367 /* Count the number of lines of a particular type currently surrounding the
 368  * given square */
 369 static int square_order(const game_state* state, int i, int j, char line_type)
 370 {
 371     int n = 0;
 372
 373     if (ABOVE_SQUARE(state, i, j) == line_type)
 374         ++n;
 375     if (BELOW_SQUARE(state, i, j) == line_type)
 376         ++n;
 377     if (LEFTOF_SQUARE(state, i, j) == line_type)
 378         ++n;
 379     if (RIGHTOF_SQUARE(state, i, j) == line_type)
 380         ++n;
 381
 382     return n;
 383 }
 384
 385 /* Set all lines bordering a dot of type old_type to type new_type
 386  * Return value tells caller whether this function actually did anything */
 387 static int dot_setall(game_state *state, int i, int j,
 388                        char old_type, char new_type)
 389 {
 390     int retval = FALSE;
 391     if (old_type == new_type)
 392         return FALSE;
 393
 394     if (i > 0        && LEFTOF_DOT(state, i, j) == old_type) {
 395         LV_LEFTOF_DOT(state, i, j) = new_type;
 396         retval = TRUE;
 397     }
 398
 399     if (i < state->w && RIGHTOF_DOT(state, i, j) == old_type) {
 400         LV_RIGHTOF_DOT(state, i, j) = new_type;
 401         retval = TRUE;
 402     }
 403
 404     if (j > 0        && ABOVE_DOT(state, i, j) == old_type) {
 405         LV_ABOVE_DOT(state, i, j) = new_type;
 406         retval = TRUE;
 407     }
 408
 409     if (j < state->h && BELOW_DOT(state, i, j) == old_type) {
 410         LV_BELOW_DOT(state, i, j) = new_type;
 411         retval = TRUE;
 412     }
 413
 414     return retval;
 415 }
 416 /* Set all lines bordering a square of type old_type to type new_type */
 417 static void square_setall(game_state *state, int i, int j,
 418                           char old_type, char new_type)
 419 {
 420     if (ABOVE_SQUARE(state, i, j) == old_type)
 421         ABOVE_SQUARE(state, i, j) = new_type;
 422     if (BELOW_SQUARE(state, i, j) == old_type)
 423         BELOW_SQUARE(state, i, j) = new_type;
 424     if (LEFTOF_SQUARE(state, i, j) == old_type)
 425         LEFTOF_SQUARE(state, i, j) = new_type;
 426     if (RIGHTOF_SQUARE(state, i, j) == old_type)
 427         RIGHTOF_SQUARE(state, i, j) = new_type;
 428 }
 429
 430 static game_params *default_params(void)
 431 {
 432     game_params *ret = snew(game_params);
 433
 434 #ifdef SLOW_SYSTEM
 435     ret->h = 4;
 436     ret->w = 4;
 437 #else
 438     ret->h = 10;
 439     ret->w = 10;
 440 #endif
 441     ret->diff = DIFF_EASY;
 442     ret->rec = 0;
 443
 444     return ret;
 445 }
 446
 447 static game_params *dup_params(game_params *params)
 448 {
 449     game_params *ret = snew(game_params);
 450     *ret = *params;                       /* structure copy */
 451     return ret;
 452 }
 453
 454 static const struct {
 455     char *desc;
 456     game_params params;
 457 } loopy_presets[] = {
 458     { "4x4 Easy",     {  4,  4, DIFF_EASY, 0 } },
 459     { "4x4 Normal",   {  4,  4, DIFF_NORMAL, 0 } },
 460     { "7x7 Easy",     {  7,  7, DIFF_EASY, 0 } },
 461     { "7x7 Normal",   {  7,  7, DIFF_NORMAL, 0 } },
 462     { "10x10 Easy",   { 10, 10, DIFF_EASY, 0 } },
 463     { "10x10 Normal", { 10, 10, DIFF_NORMAL, 0 } },
 464 #ifndef SLOW_SYSTEM
 465     { "15x15 Easy",   { 15, 15, DIFF_EASY, 0 } },
 466     { "15x15 Normal", { 15, 15, DIFF_NORMAL, 0 } },
 467     { "30x20 Easy",   { 30, 20, DIFF_EASY, 0 } },
 468     { "30x20 Normal", { 30, 20, DIFF_NORMAL, 0 } }
 469 #endif
 470 };
 471
 472 static int game_fetch_preset(int i, char **name, game_params **params)
 473 {
 474     game_params tmppar;
 475
 476     if (i < 0 || i >= lenof(loopy_presets))
 477         return FALSE;
 478
 479     tmppar = loopy_presets[i].params;
 480     *params = dup_params(&tmppar);
 481     *name = dupstr(loopy_presets[i].desc);
 482
 483     return TRUE;
 484 }
 485
 486 static void free_params(game_params *params)
 487 {
 488     sfree(params);
 489 }
 490
 491 static void decode_params(game_params *params, char const *string)
 492 {
 493     params->h = params->w = atoi(string);
 494     params->rec = 0;
 495     params->diff = DIFF_EASY;
 496     while (*string && isdigit((unsigned char)*string)) string++;
 497     if (*string == 'x') {
 498         string++;
 499         params->h = atoi(string);
 500         while (*string && isdigit((unsigned char)*string)) string++;
 501     }
 502     if (*string == 'r') {
 503         string++;
 504         params->rec = atoi(string);
 505         while (*string && isdigit((unsigned char)*string)) string++;
 506     }
 507     if (*string == 'd') {
 508         int i;
 509
 510         string++;
 511         for (i = 0; i < DIFFCOUNT; i++)
 512             if (*string == loopy_diffchars[i])
 513                 params->diff = i;
 514         if (*string) string++;
 515     }
 516 }
 517
 518 static char *encode_params(game_params *params, int full)
 519 {
 520     char str[80];
 521     sprintf(str, "%dx%d", params->w, params->h);
 522     if (full)
 523         sprintf(str + strlen(str), "r%dd%c", params->rec,
 524                 loopy_diffchars[params->diff]);
 525     return dupstr(str);
 526 }
 527
 528 static config_item *game_configure(game_params *params)
 529 {
 530     config_item *ret;
 531     char buf[80];
 532
 533     ret = snewn(4, config_item);
 534
 535     ret[0].name = "Width";
 536     ret[0].type = C_STRING;
 537     sprintf(buf, "%d", params->w);
 538     ret[0].sval = dupstr(buf);
 539     ret[0].ival = 0;
 540
 541     ret[1].name = "Height";
 542     ret[1].type = C_STRING;
 543     sprintf(buf, "%d", params->h);
 544     ret[1].sval = dupstr(buf);
 545     ret[1].ival = 0;
 546
 547     ret[2].name = "Difficulty";
 548     ret[2].type = C_CHOICES;
 549     ret[2].sval = DIFFCONFIG;
 550     ret[2].ival = params->diff;
 551
 552     ret[3].name = NULL;
 553     ret[3].type = C_END;
 554     ret[3].sval = NULL;
 555     ret[3].ival = 0;
 556
 557     return ret;
 558 }
 559
 560 static game_params *custom_params(config_item *cfg)
 561 {
 562     game_params *ret = snew(game_params);
 563
 564     ret->w = atoi(cfg[0].sval);
 565     ret->h = atoi(cfg[1].sval);
 566     ret->rec = 0;
 567     ret->diff = cfg[2].ival;
 568
 569     return ret;
 570 }
 571
 572 static char *validate_params(game_params *params, int full)
 573 {
 574     if (params->w < 4 || params->h < 4)
 575         return "Width and height must both be at least 4";
 576     if (params->rec < 0)
 577         return "Recursion depth can't be negative";
 578
 579     /*
 580      * This shouldn't be able to happen at all, since decode_params
 581      * and custom_params will never generate anything that isn't
 582      * within range.
 583      */
 584     assert(params->diff >= 0 && params->diff < DIFFCOUNT);
 585
 586     return NULL;
 587 }
 588
 589 /* We're going to store a list of current candidate squares for lighting.
 590  * Each square gets a 'score', which tells us how adding that square right
 591  * now would affect the length of the solution loop.  We're trying to
 592  * maximise that quantity so will bias our random selection of squares to
 593  * light towards those with high scores */
 594 struct square {
 595     int score;
 596     unsigned long random;
 597     int x, y;
 598 };
 599
 600 static int get_square_cmpfn(void *v1, void *v2)
 601 {
 602     struct square *s1 = (struct square *)v1;
 603     struct square *s2 = (struct square *)v2;
 604     int r;
 605
 606     r = s1->x - s2->x;
 607     if (r)
 608         return r;
 609
 610     r = s1->y - s2->y;
 611     if (r)
 612         return r;
 613
 614     return 0;
 615 }
 616
 617 static int square_sort_cmpfn(void *v1, void *v2)
 618 {
 619     struct square *s1 = (struct square *)v1;
 620     struct square *s2 = (struct square *)v2;
 621     int r;
 622
 623     r = s2->score - s1->score;
 624     if (r) {
 625         return r;
 626     }
 627
 628     if (s1->random < s2->random)
 629         return -1;
 630     else if (s1->random > s2->random)
 631         return 1;
 632
 633     /*
 634      * It's _just_ possible that two squares might have been given
 635      * the same random value. In that situation, fall back to
 636      * comparing based on the coordinates. This introduces a tiny
 637      * directional bias, but not a significant one.
 638      */
 639     return get_square_cmpfn(v1, v2);
 640 }
 641
 642 static void print_tree(tree234 *tree)
 643 {
 644 #if 0
 645     int i = 0;
 646     struct square *s;
 647     printf("Print tree:\n");
 648     while (i < count234(tree)) {
 649         s = (struct square *)index234(tree, i);
 650         assert(s);
 651         printf("  [%d,%d], %d, %d\n", s->x, s->y, s->score, s->random);
 652         ++i;
 653     }
 654 #endif
 655 }
 656
 657 enum { SQUARE_LIT, SQUARE_UNLIT };
 658
 659 #define SQUARE_STATE(i, j)                 \
 660     (((i) < 0 || (i) >= params->w ||       \
 661       (j) < 0 || (j) >= params->h) ?       \
 662      SQUARE_UNLIT :  LV_SQUARE_STATE(i,j))
 663
 664 #define LV_SQUARE_STATE(i, j) board[(i) + params->w * (j)]
 665
 666 static void print_board(const game_params *params, const char *board)
 667 {
 668 #if 0
 669     int i,j;
 670
 671     printf(" ");
 672     for (i = 0; i < params->w; i++) {
 673         printf("%d", i%10);
 674     }
 675     printf("\n");
 676     for (j = 0; j < params->h; j++) {
 677         printf("%d", j%10);
 678         for (i = 0; i < params->w; i++) {
 679             printf("%c", SQUARE_STATE(i, j) ? ' ' : 'O');
 680         }
 681         printf("\n");
 682     }
 683 #endif
 684 }
 685
 686 static void add_full_clues(game_state *state, game_params *params,
 687                            random_state *rs)
 688 {
 689     char *clues;
 690     char *board;
 691     int i, j, a, b, c;
 692     int board_area = SQUARE_COUNT(params);
 693     int t;
 694
 695     struct square *square, *tmpsquare, *sq;
 696     struct square square_pos;
 697
 698     /* These will contain exactly the same information, sorted into different
 699      * orders */
 700     tree234 *lightable_squares_sorted, *lightable_squares_gettable;
 701
 702 #define SQUARE_REACHABLE(i,j)                      \
 703      (t = (SQUARE_STATE(i-1, j) == SQUARE_LIT ||      \
 704            SQUARE_STATE(i+1, j) == SQUARE_LIT ||      \
 705            SQUARE_STATE(i, j-1) == SQUARE_LIT ||      \
 706            SQUARE_STATE(i, j+1) == SQUARE_LIT),       \
 707 /*      printf("SQUARE_REACHABLE(%d,%d) = %d\n", i, j, t), */ \
 708       t)
 709
 710
 711     /* One situation in which we may not light a square is if that'll leave one
 712      * square above/below and one left/right of us unlit, separated by a lit
 713      * square diagnonal from us */
 714 #define SQUARE_DIAGONAL_VIOLATION(i, j, h, v)           \
 715     (t = (SQUARE_STATE((i)+(h), (j))     == SQUARE_UNLIT && \
 716           SQUARE_STATE((i),     (j)+(v)) == SQUARE_UNLIT && \
 717           SQUARE_STATE((i)+(h), (j)+(v)) == SQUARE_LIT),    \
 718 /*     t ? printf("SQUARE_DIAGONAL_VIOLATION(%d, %d, %d, %d)\n",
 719                   i, j, h, v) : 0,*/ \
 720      t)
 721
 722     /* We also may not light a square if it will form a loop of lit squares
 723      * around some unlit squares, as then the game soln won't have a single
 724      * loop */
 725 #define SQUARE_LOOP_VIOLATION(i, j, lit1, lit2) \
 726     (SQUARE_STATE((i)+1, (j)) == lit1    &&     \
 727      SQUARE_STATE((i)-1, (j)) == lit1    &&     \
 728      SQUARE_STATE((i), (j)+1) == lit2    &&     \
 729      SQUARE_STATE((i), (j)-1) == lit2)
 730
 731 #define CAN_LIGHT_SQUARE(i, j)                                 \
 732     (SQUARE_REACHABLE(i, j)                                 && \
 733      !SQUARE_DIAGONAL_VIOLATION(i, j, -1, -1)               && \
 734      !SQUARE_DIAGONAL_VIOLATION(i, j, +1, -1)               && \
 735      !SQUARE_DIAGONAL_VIOLATION(i, j, -1, +1)               && \
 736      !SQUARE_DIAGONAL_VIOLATION(i, j, +1, +1)               && \
 737      !SQUARE_LOOP_VIOLATION(i, j, SQUARE_LIT, SQUARE_UNLIT) && \
 738      !SQUARE_LOOP_VIOLATION(i, j, SQUARE_UNLIT, SQUARE_LIT))
 739
 740 #define IS_LIGHTING_CANDIDATE(i, j)        \
 741     (SQUARE_STATE(i, j) == SQUARE_UNLIT && \
 742      CAN_LIGHT_SQUARE(i,j))
 743
 744     /* The 'score' of a square reflects its current desirability for selection
 745      * as the next square to light.  We want to encourage moving into uncharted
 746      * areas so we give scores according to how many of the square's neighbours
 747      * are currently unlit. */
 748
 749    /* UNLIT    SCORE
 750     *   3        2
 751     *   2        0
 752     *   1       -2
 753     */
 754 #define SQUARE_SCORE(i,j)                  \
 755     (2*((SQUARE_STATE(i-1, j) == SQUARE_UNLIT)  +   \
 756         (SQUARE_STATE(i+1, j) == SQUARE_UNLIT)  +   \
 757         (SQUARE_STATE(i, j-1) == SQUARE_UNLIT)  +   \
 758         (SQUARE_STATE(i, j+1) == SQUARE_UNLIT)) - 4)
 759
 760     /* When a square gets lit, this defines how far away from that square we
 761      * need to go recomputing scores */
 762 #define SCORE_DISTANCE 1
 763
 764     board = snewn(board_area, char);
 765     clues = state->clues;
 766
 767     /* Make a board */
 768     memset(board, SQUARE_UNLIT, board_area);
 769
 770     /* Seed the board with a single lit square near the middle */
 771     i = params->w / 2;
 772     j = params->h / 2;
 773     if (params->w & 1 && random_bits(rs, 1))
 774         ++i;
 775     if (params->h & 1 && random_bits(rs, 1))
 776         ++j;
 777
 778     LV_SQUARE_STATE(i, j) = SQUARE_LIT;
 779
 780     /* We need a way of favouring squares that will increase our loopiness.
 781      * We do this by maintaining a list of all candidate squares sorted by
 782      * their score and choose randomly from that with appropriate skew.
 783      * In order to avoid consistently biasing towards particular squares, we
 784      * need the sort order _within_ each group of scores to be completely
 785      * random.  But it would be abusing the hospitality of the tree234 data
 786      * structure if our comparison function were nondeterministic :-).  So with
 787      * each square we associate a random number that does not change during a
 788      * particular run of the generator, and use that as a secondary sort key.
 789      * Yes, this means we will be biased towards particular random squares in
 790      * any one run but that doesn't actually matter. */
 791
 792     lightable_squares_sorted   = newtree234(square_sort_cmpfn);
 793     lightable_squares_gettable = newtree234(get_square_cmpfn);
 794 #define ADD_SQUARE(s)                                          \
 795     do {                                                       \
 796 /*      printf("ADD SQUARE: [%d,%d], %d, %d\n",
 797                s->x, s->y, s->score, s->random);*/ \
 798         sq = add234(lightable_squares_sorted, s);              \
 799         assert(sq == s);                                       \
 800         sq = add234(lightable_squares_gettable, s);            \
 801         assert(sq == s);                                       \
 802     } while (0)
 803
 804 #define REMOVE_SQUARE(s)                                       \
 805     do {                                                       \
 806 /*      printf("DELETE SQUARE: [%d,%d], %d, %d\n",
 807                s->x, s->y, s->score, s->random);*/ \
 808         sq = del234(lightable_squares_sorted, s);              \
 809         assert(sq);                                            \
 810         sq = del234(lightable_squares_gettable, s);            \
 811         assert(sq);                                            \
 812     } while (0)
 813
 814 #define HANDLE_DIR(a, b)                                       \
 815     square = snew(struct square);                              \
 816     square->x = (i)+(a);                                       \
 817     square->y = (j)+(b);                                       \
 818     square->score = 2;                                         \
 819     square->random = random_bits(rs, 31);                      \
 820     ADD_SQUARE(square);
 821     HANDLE_DIR(-1, 0);
 822     HANDLE_DIR( 1, 0);
 823     HANDLE_DIR( 0,-1);
 824     HANDLE_DIR( 0, 1);
 825 #undef HANDLE_DIR
 826
 827     /* Light squares one at a time until the board is interesting enough */
 828     while (TRUE)
 829     {
 830         /* We have count234(lightable_squares) possibilities, and in
 831          * lightable_squares_sorted they are sorted with the most desirable
 832          * first.  */
 833         c = count234(lightable_squares_sorted);
 834         if (c == 0)
 835             break;
 836         assert(c == count234(lightable_squares_gettable));
 837
 838         /* Check that the best square available is any good */
 839         square = (struct square *)index234(lightable_squares_sorted, 0);
 840         assert(square);
 841
 842         /*
 843          * We never want to _decrease_ the loop's perimeter. Making
 844          * moves that leave the perimeter the same is occasionally
 845          * useful: if it were _never_ done then the user would be
 846          * able to deduce illicitly that any degree-zero vertex was
 847          * on the outside of the loop. So we do it sometimes but
 848          * not always.
 849          */
 850         if (square->score < 0 || (square->score == 0 &&
 851                                   random_upto(rs, 2) == 0))
 852             break;
 853
 854         print_tree(lightable_squares_sorted);
 855         assert(square->score == SQUARE_SCORE(square->x, square->y));
 856         assert(SQUARE_STATE(square->x, square->y) == SQUARE_UNLIT);
 857         assert(square->x >= 0 && square->x < params->w);
 858         assert(square->y >= 0 && square->y < params->h);
 859 /*        printf("LIGHT SQUARE: [%d,%d], score = %d\n", square->x, square->y, square->score); */
 860
 861         /* Update data structures */
 862         LV_SQUARE_STATE(square->x, square->y) = SQUARE_LIT;
 863         REMOVE_SQUARE(square);
 864
 865         print_board(params, board);
 866
 867         /* We might have changed the score of any squares up to 2 units away in
 868          * any direction */
 869         for (b = -SCORE_DISTANCE; b <= SCORE_DISTANCE; b++) {
 870             for (a = -SCORE_DISTANCE; a <= SCORE_DISTANCE; a++) {
 871                 if (!a && !b)
 872                     continue;
 873                 square_pos.x = square->x + a;
 874                 square_pos.y = square->y + b;
 875 /*                printf("Refreshing score for [%d,%d]:\n", square_pos.x, square_pos.y); */
 876                 if (square_pos.x < 0 || square_pos.x >= params->w ||
 877                     square_pos.y < 0 || square_pos.y >= params->h) {
 878 /*                    printf("  Out of bounds\n"); */
 879                    continue;
 880                 }
 881                 tmpsquare = find234(lightable_squares_gettable, &square_pos,
 882                                     NULL);
 883                 if (tmpsquare) {
 884 /*                    printf(" Removing\n"); */
 885                     assert(tmpsquare->x == square_pos.x);
 886                     assert(tmpsquare->y == square_pos.y);
 887                     assert(SQUARE_STATE(tmpsquare->x, tmpsquare->y) ==
 888                            SQUARE_UNLIT);
 889                     REMOVE_SQUARE(tmpsquare);
 890                 } else {
 891 /*                    printf(" Creating\n"); */
 892                     tmpsquare = snew(struct square);
 893                     tmpsquare->x = square_pos.x;
 894                     tmpsquare->y = square_pos.y;
 895                     tmpsquare->random = random_bits(rs, 31);
 896                 }
 897                 tmpsquare->score = SQUARE_SCORE(tmpsquare->x, tmpsquare->y);
 898
 899                 if (IS_LIGHTING_CANDIDATE(tmpsquare->x, tmpsquare->y)) {
 900 /*                    printf(" Adding\n"); */
 901                     ADD_SQUARE(tmpsquare);
 902                 } else {
 903 /*                    printf(" Destroying\n"); */
 904                     sfree(tmpsquare);
 905                 }
 906             }
 907         }
 908         sfree(square);
 909 /*        printf("\n\n"); */
 910     }
 911
 912     while ((square = delpos234(lightable_squares_gettable, 0)) != NULL)
 913         sfree(square);
 914     freetree234(lightable_squares_gettable);
 915     freetree234(lightable_squares_sorted);
 916
 917     /* Copy out all the clues */
 918     for (j = 0; j < params->h; ++j) {
 919         for (i = 0; i < params->w; ++i) {
 920             c = SQUARE_STATE(i, j);
 921             LV_CLUE_AT(state, i, j) = '0';
 922             if (SQUARE_STATE(i-1, j) != c) ++LV_CLUE_AT(state, i, j);
 923             if (SQUARE_STATE(i+1, j) != c) ++LV_CLUE_AT(state, i, j);
 924             if (SQUARE_STATE(i, j-1) != c) ++LV_CLUE_AT(state, i, j);
 925             if (SQUARE_STATE(i, j+1) != c) ++LV_CLUE_AT(state, i, j);
 926         }
 927     }
 928
 929     sfree(board);
 930 }
 931
 932 static solver_state *solve_game_rec(const solver_state *sstate, int diff);
 933
 934 static int game_has_unique_soln(const game_state *state, int diff)
 935 {
 936     int ret;
 937     solver_state *sstate_new;
 938     solver_state *sstate = new_solver_state((game_state *)state);
 939
 940     sstate_new = solve_game_rec(sstate, diff);
 941
 942     ret = (sstate_new->solver_status == SOLVER_SOLVED);
 943
 944     free_solver_state(sstate_new);
 945     free_solver_state(sstate);
 946
 947     return ret;
 948 }
 949
 950 /* Remove clues one at a time at random. */
 951 static game_state *remove_clues(game_state *state, random_state *rs, int diff)
 952 {
 953     int *square_list, squares;
 954     game_state *ret = dup_game(state), *saved_ret;
 955     int n;
 956
 957     /* We need to remove some clues.  We'll do this by forming a list of all
 958      * available equivalence classes, shuffling it, then going along one at a
 959      * time clearing every member of each equivalence class, where removing a
 960      * class doesn't render the board unsolvable. */
 961     squares = state->w * state->h;
 962     square_list = snewn(squares, int);
 963     for (n = 0; n < squares; ++n) {
 964         square_list[n] = n;
 965     }
 966
 967     shuffle(square_list, squares, sizeof(int), rs);
 968
 969     for (n = 0; n < squares; ++n) {
 970         saved_ret = dup_game(ret);
 971         LV_CLUE_AT(ret, square_list[n] % state->w,
 972                    square_list[n] / state->w) = ' ';
 973         if (game_has_unique_soln(ret, diff)) {
 974             free_game(saved_ret);
 975         } else {
 976             free_game(ret);
 977             ret = saved_ret;
 978         }
 979     }
 980     sfree(square_list);
 981
 982     return ret;
 983 }
 984
 985 static char *validate_desc(game_params *params, char *desc);
 986
 987 static char *new_game_desc(game_params *params, random_state *rs,
 988                            char **aux, int interactive)
 989 {
 990     /* solution and description both use run-length encoding in obvious ways */
 991     char *retval;
 992     char *description = snewn(SQUARE_COUNT(params) + 1, char);
 993     char *dp = description;
 994     int i, j;
 995     int empty_count;
 996     game_state *state = snew(game_state), *state_new;
 997
 998     state->h = params->h;
 999     state->w = params->w;
1000
1001     state->clues = snewn(SQUARE_COUNT(params), char);
1002     state->hl = snewn(HL_COUNT(params), char);
1003     state->vl = snewn(VL_COUNT(params), char);
1004
1005 newboard_please:
1006     memset(state->hl, LINE_UNKNOWN, HL_COUNT(params));
1007     memset(state->vl, LINE_UNKNOWN, VL_COUNT(params));
1008
1009     state->solved = state->cheated = FALSE;
1010     state->recursion_depth = params->rec;
1011
1012     /* Get a new random solvable board with all its clues filled in.  Yes, this
1013      * can loop for ever if the params are suitably unfavourable, but
1014      * preventing games smaller than 4x4 seems to stop this happening */
1015
1016     do {
1017         add_full_clues(state, params, rs);
1018     } while (!game_has_unique_soln(state, params->diff));
1019
1020     state_new = remove_clues(state, rs, params->diff);
1021     free_game(state);
1022     state = state_new;
1023
1024     if (params->diff > 0 && game_has_unique_soln(state, params->diff-1)) {
1025         /* Board is too easy */
1026         goto newboard_please;
1027     }
1028
1029     empty_count = 0;
1030     for (j = 0; j < params->h; ++j) {
1031         for (i = 0; i < params->w; ++i) {
1032             if (CLUE_AT(state, i, j) == ' ') {
1033                 if (empty_count > 25) {
1034                     dp += sprintf(dp, "%c", (int)(empty_count + 'a' - 1));
1035                     empty_count = 0;
1036                 }
1037                 empty_count++;
1038             } else {
1039                 if (empty_count) {
1040                     dp += sprintf(dp, "%c", (int)(empty_count + 'a' - 1));
1041                     empty_count = 0;
1042                 }
1043                 dp += sprintf(dp, "%c", (int)(CLUE_AT(state, i, j)));
1044             }
1045         }
1046     }
1047     if (empty_count)
1048         dp += sprintf(dp, "%c", (int)(empty_count + 'a' - 1));
1049
1050     free_game(state);
1051     retval = dupstr(description);
1052     sfree(description);
1053
1054     assert(!validate_desc(params, retval));
1055
1056     return retval;
1057 }
1058
1059 /* We require that the params pass the test in validate_params and that the
1060  * description fills the entire game area */
1061 static char *validate_desc(game_params *params, char *desc)
1062 {
1063     int count = 0;
1064
1065     for (; *desc; ++desc) {
1066         if (*desc >= '0' && *desc <= '9') {
1067             count++;
1068             continue;
1069         }
1070         if (*desc >= 'a') {
1071             count += *desc - 'a' + 1;
1072             continue;
1073         }
1074         return "Unknown character in description";
1075     }
1076
1077     if (count < SQUARE_COUNT(params))
1078         return "Description too short for board size";
1079     if (count > SQUARE_COUNT(params))
1080         return "Description too long for board size";
1081
1082     return NULL;
1083 }
1084
1085 static game_state *new_game(midend *me, game_params *params, char *desc)
1086 {
1087     int i,j;
1088     game_state *state = snew(game_state);
1089     int empties_to_make = 0;
1090     int n;
1091     const char *dp = desc;
1092
1093     state->recursion_depth = 0; /* XXX pending removal, probably */
1094
1095     state->h = params->h;
1096     state->w = params->w;
1097
1098     state->clues = snewn(SQUARE_COUNT(params), char);
1099     state->hl    = snewn(HL_COUNT(params), char);
1100     state->vl    = snewn(VL_COUNT(params), char);
1101
1102     state->solved = state->cheated = FALSE;
1103
1104     for (j = 0 ; j < params->h; ++j) {
1105         for (i = 0 ; i < params->w; ++i) {
1106             if (empties_to_make) {
1107                 empties_to_make--;
1108                 LV_CLUE_AT(state, i, j) = ' ';
1109                 continue;
1110             }
1111
1112             assert(*dp);
1113             n = *dp - '0';
1114             if (n >=0 && n < 10) {
1115                 LV_CLUE_AT(state, i, j) = *dp;
1116             } else {
1117                 n = *dp - 'a' + 1;
1118                 assert(n > 0);
1119                 LV_CLUE_AT(state, i, j) = ' ';
1120                 empties_to_make = n - 1;
1121             }
1122             ++dp;
1123         }
1124     }
1125
1126     memset(state->hl, LINE_UNKNOWN, HL_COUNT(params));
1127     memset(state->vl, LINE_UNKNOWN, VL_COUNT(params));
1128
1129     return state;
1130 }
1131
1132 enum { LOOP_NONE=0, LOOP_SOLN, LOOP_NOT_SOLN };
1133
1134 /* Sums the lengths of the numbers in range [0,n) */
1135 /* See equivalent function in solo.c for justification of this. */
1136 static int len_0_to_n(int n)
1137 {
1138     int len = 1; /* Counting 0 as a bit of a special case */
1139     int i;
1140
1141     for (i = 1; i < n; i *= 10) {
1142         len += max(n - i, 0);
1143     }
1144
1145     return len;
1146 }
1147
1148 static char *encode_solve_move(const game_state *state)
1149 {
1150     int len, i, j;
1151     char *ret, *p;
1152     /* This is going to return a string representing the moves needed to set
1153      * every line in a grid to be the same as the ones in 'state'.  The exact
1154      * length of this string is predictable. */
1155
1156     len = 1;  /* Count the 'S' prefix */
1157     /* Numbers in horizontal lines */
1158     /* Horizontal lines, x position */
1159     len += len_0_to_n(state->w) * (state->h + 1);
1160     /* Horizontal lines, y position */
1161     len += len_0_to_n(state->h + 1) * (state->w);
1162     /* Vertical lines, y position */
1163     len += len_0_to_n(state->h) * (state->w + 1);
1164     /* Vertical lines, x position */
1165     len += len_0_to_n(state->w + 1) * (state->h);
1166     /* For each line we also have two letters and a comma */
1167     len += 3 * (HL_COUNT(state) + VL_COUNT(state));
1168
1169     ret = snewn(len + 1, char);
1170     p = ret;
1171
1172     p += sprintf(p, "S");
1173
1174     for (j = 0; j < state->h + 1; ++j) {
1175         for (i = 0; i < state->w; ++i) {
1176             switch (RIGHTOF_DOT(state, i, j)) {
1177                 case LINE_YES:
1178                     p += sprintf(p, "%d,%dhy", i, j);
1179                     break;
1180                 case LINE_NO:
1181                     p += sprintf(p, "%d,%dhn", i, j);
1182                     break;
1183 /*                default: */
1184                     /* I'm going to forgive this because I think the results
1185                      * are cute. */
1186 /*                    assert(!"Solver produced incomplete solution!"); */
1187             }
1188         }
1189     }
1190
1191     for (j = 0; j < state->h; ++j) {
1192         for (i = 0; i < state->w + 1; ++i) {
1193             switch (BELOW_DOT(state, i, j)) {
1194                 case LINE_YES:
1195                     p += sprintf(p, "%d,%dvy", i, j);
1196                     break;
1197                 case LINE_NO:
1198                     p += sprintf(p, "%d,%dvn", i, j);
1199                     break;
1200 /*                default: */
1201                     /* I'm going to forgive this because I think the results
1202                      * are cute. */
1203 /*                    assert(!"Solver produced incomplete solution!"); */
1204             }
1205         }
1206     }
1207
1208     /*
1209      * Ensure we haven't overrun the buffer we allocated (which we
1210      * really shouldn't have, since we computed its maximum size).
1211      * Note that this assert is <= rather than ==, because the
1212      * solver is permitted to produce an incomplete solution in
1213      * which case the buffer will be only partially used.
1214      */
1215     assert(strlen(ret) <= (size_t)len);
1216     return ret;
1217 }
1218
1219 /* BEGIN SOLVER IMPLEMENTATION */
1220
1221    /* For each pair of lines through each dot we store a bit for whether
1222     * exactly one of those lines is ON, and in separate arrays we store whether
1223     * at least one is on and whether at most 1 is on.  (If we know both or
1224     * neither is on that's already stored more directly.)  That's six bits per
1225     * dot.  Bit number n represents the lines shown in dot_type_dirs[n]. */
1226
1227 enum dline {
1228     DLINE_VERT  = 0,
1229     DLINE_HORIZ = 1,
1230     DLINE_UL    = 2,
1231     DLINE_DR    = 3,
1232     DLINE_UR    = 4,
1233     DLINE_DL    = 5
1234 };
1235
1236 #define OPP_DLINE(dline) (dline ^ 1)
1237
1238
1239 #define SQUARE_DLINES                                                          \
1240                    HANDLE_DLINE(DLINE_UL, RIGHTOF_SQUARE, BELOW_SQUARE, 1, 1); \
1241                    HANDLE_DLINE(DLINE_UR, LEFTOF_SQUARE,  BELOW_SQUARE, 0, 1); \
1242                    HANDLE_DLINE(DLINE_DL, RIGHTOF_SQUARE, ABOVE_SQUARE, 1, 0); \
1243                    HANDLE_DLINE(DLINE_DR, LEFTOF_SQUARE,  ABOVE_SQUARE, 0, 0);
1244
1245 #define DOT_DLINES                                                       \
1246                    HANDLE_DLINE(DLINE_VERT,  ABOVE_DOT,  BELOW_DOT);     \
1247                    HANDLE_DLINE(DLINE_HORIZ, LEFTOF_DOT, RIGHTOF_DOT);   \
1248                    HANDLE_DLINE(DLINE_UL,    ABOVE_DOT,  LEFTOF_DOT);    \
1249                    HANDLE_DLINE(DLINE_UR,    ABOVE_DOT,  RIGHTOF_DOT);   \
1250                    HANDLE_DLINE(DLINE_DL,    BELOW_DOT,  LEFTOF_DOT);    \
1251                    HANDLE_DLINE(DLINE_DR,    BELOW_DOT,  RIGHTOF_DOT);
1252
1253 static void array_setall(char *array, char from, char to, int len)
1254 {
1255     char *p = array, *p_old = p;
1256     int len_remaining = len;
1257
1258     while ((p = memchr(p, from, len_remaining))) {
1259         *p = to;
1260         len_remaining -= p - p_old;
1261         p_old = p;
1262     }
1263 }
1264
1265 static int dot_setall_dlines(solver_state *sstate, enum dline dl, int i, int j,
1266                              enum line_state line_old, enum line_state line_new)
1267 {
1268     game_state *state = sstate->state;
1269     int retval = FALSE;
1270
1271     if (line_old == line_new)
1272         return FALSE;
1273
1274     /* First line in dline */
1275     switch (dl) {
1276         case DLINE_UL:
1277         case DLINE_UR:
1278         case DLINE_VERT:
1279             if (j > 0 && ABOVE_DOT(state, i, j) == line_old) {
1280                 LV_ABOVE_DOT(state, i, j) = line_new;
1281                 retval = TRUE;
1282             }
1283             break;
1284         case DLINE_DL:
1285         case DLINE_DR:
1286             if (j < (state)->h && BELOW_DOT(state, i, j) == line_old) {
1287                 LV_BELOW_DOT(state, i, j) = line_new;
1288                 retval = TRUE;
1289             }
1290             break;
1291         case DLINE_HORIZ:
1292             if (i > 0 && LEFTOF_DOT(state, i, j) == line_old) {
1293                 LV_LEFTOF_DOT(state, i, j) = line_new;
1294                 retval = TRUE;
1295             }
1296             break;
1297     }
1298
1299     /* Second line in dline */
1300     switch (dl) {
1301         case DLINE_UL:
1302         case DLINE_DL:
1303             if (i > 0 && LEFTOF_DOT(state, i, j) == line_old) {
1304                 LV_LEFTOF_DOT(state, i, j) = line_new;
1305                 retval = TRUE;
1306             }
1307             break;
1308         case DLINE_UR:
1309         case DLINE_DR:
1310         case DLINE_HORIZ:
1311             if (i < (state)->w && RIGHTOF_DOT(state, i, j) == line_old) {
1312                 LV_RIGHTOF_DOT(state, i, j) = line_new;
1313                 retval = TRUE;
1314             }
1315             break;
1316         case DLINE_VERT:
1317             if (j < (state)->h && BELOW_DOT(state, i, j) == line_old) {
1318                 LV_BELOW_DOT(state, i, j) = line_new;
1319                 retval = TRUE;
1320             }
1321             break;
1322     }
1323
1324     return retval;
1325 }
1326
1327 #if 0
1328 /* This will fail an assertion if {dx,dy} are anything other than {-1,0}, {1,0}
1329  * {0,-1} or {0,1} */
1330 static int line_status_from_point(const game_state *state,
1331                                   int x, int y, int dx, int dy)
1332 {
1333     if (dx == -1 && dy ==  0)
1334         return LEFTOF_DOT(state, x, y);
1335     if (dx ==  1 && dy ==  0)
1336         return RIGHTOF_DOT(state, x, y);
1337     if (dx ==  0 && dy == -1)
1338         return ABOVE_DOT(state, x, y);
1339     if (dx ==  0 && dy ==  1)
1340         return BELOW_DOT(state, x, y);
1341
1342     assert(!"Illegal dx or dy in line_status_from_point");
1343     return 0;
1344 }
1345 #endif
1346
1347 /* This will return a dynamically allocated solver_state containing the (more)
1348  * solved grid */
1349 static solver_state *solve_game_rec(const solver_state *sstate_start, int diff)
1350 {
1351    int i, j, w, h;
1352    int current_yes, current_no, desired;
1353    solver_state *sstate, *sstate_saved, *sstate_tmp;
1354    int t;
1355    solver_state *sstate_rec_solved;
1356    int recursive_soln_count;
1357    char *square_solved;
1358    char *dot_solved;
1359    int solver_progress;
1360
1361    h = sstate_start->state->h;
1362    w = sstate_start->state->w;
1363
1364    dot_solved = snewn(DOT_COUNT(sstate_start->state), char);
1365    square_solved = snewn(SQUARE_COUNT(sstate_start->state), char);
1366    memset(dot_solved, FALSE, DOT_COUNT(sstate_start->state));
1367    memset(square_solved, FALSE, SQUARE_COUNT(sstate_start->state));
1368
1369 #if 0
1370    printf("solve_game_rec: recursion_remaining = %d\n",
1371           sstate_start->recursion_remaining);
1372 #endif
1373
1374    sstate = dup_solver_state((solver_state *)sstate_start);
1375
1376 #define FOUND_MISTAKE                                    \
1377    do {                                                  \
1378        sstate->solver_status = SOLVER_MISTAKE;           \
1379        sfree(dot_solved);  sfree(square_solved);         \
1380        free_solver_state(sstate_saved);                  \
1381        return sstate;                                    \
1382    } while (0)
1383
1384    sstate_saved = NULL;
1385
1386 nonrecursive_solver:
1387
1388    while (1) {
1389        solver_progress = FALSE;
1390
1391        /* First we do the 'easy' work, that might cause concrete results */
1392
1393        /* Per-square deductions */
1394        for (j = 0; j < h; ++j) {
1395            for (i = 0; i < w; ++i) {
1396                /* Begin rules that look at the clue (if there is one) */
1397                if (square_solved[i + j*w])
1398                    continue;
1399
1400                desired = CLUE_AT(sstate->state, i, j);
1401                if (desired == ' ')
1402                    continue;
1403
1404                desired = desired - '0';
1405                current_yes = square_order(sstate->state, i, j, LINE_YES);
1406                current_no  = square_order(sstate->state, i, j, LINE_NO);
1407
1408                if (current_yes + current_no == 4)  {
1409                    square_solved[i + j*w] = TRUE;
1410                    continue;
1411                }
1412
1413                if (desired < current_yes)
1414                    FOUND_MISTAKE;
1415                if (desired == current_yes) {
1416                    square_setall(sstate->state, i, j, LINE_UNKNOWN, LINE_NO);
1417                    square_solved[i + j*w] = TRUE;
1418                    solver_progress = TRUE;
1419                    continue;
1420                }
1421
1422                if (4 - desired < current_no)
1423                    FOUND_MISTAKE;
1424                if (4 - desired == current_no) {
1425                    square_setall(sstate->state, i, j, LINE_UNKNOWN, LINE_YES);
1426                    square_solved[i + j*w] = TRUE;
1427                    solver_progress = TRUE;
1428                }
1429            }
1430        }
1431
1432        /* Per-dot deductions */
1433        for (j = 0; j < h + 1; ++j) {
1434            for (i = 0; i < w + 1; ++i) {
1435                if (dot_solved[i + j*(w+1)])
1436                    continue;
1437
1438                switch (dot_order(sstate->state, i, j, LINE_YES)) {
1439                case 0:
1440                    switch (dot_order(sstate->state, i, j, LINE_NO)) {
1441                        case 3:
1442                            dot_setall(sstate->state, i, j, LINE_UNKNOWN, LINE_NO);
1443                            solver_progress = TRUE;
1444                            /* fall through */
1445                        case 4:
1446                            dot_solved[i + j*(w+1)] = TRUE;
1447                            break;
1448                    }
1449                    break;
1450                case 1:
1451                    switch (dot_order(sstate->state, i, j, LINE_NO)) {
1452 #define H1(dline, dir1_dot, dir2_dot, dot_howmany)                             \
1453                        if (dir1_dot(sstate->state, i, j) == LINE_UNKNOWN) {    \
1454                            if (dir2_dot(sstate->state, i, j) == LINE_UNKNOWN){ \
1455                                solver_progress |=                              \
1456                                  SET_BIT(sstate->dot_howmany[i + (w + 1) * j], \
1457                                          dline);                               \
1458                            }                                                   \
1459                        }
1460                        case 1:
1461                            if (diff > DIFF_EASY) {
1462 #define HANDLE_DLINE(dline, dir1_dot, dir2_dot)                               \
1463                            H1(dline, dir1_dot, dir2_dot, dot_atleastone)
1464                                /* 1 yes, 1 no, so exactly one of unknowns is
1465                                 * yes */
1466                                DOT_DLINES;
1467 #undef HANDLE_DLINE
1468                            }
1469                            /* fall through */
1470                        case 0:
1471                            if (diff > DIFF_EASY) {
1472 #define HANDLE_DLINE(dline, dir1_dot, dir2_dot)                               \
1473                            H1(dline, dir1_dot, dir2_dot, dot_atmostone)
1474                                /* 1 yes, fewer than 2 no, so at most one of
1475                                 * unknowns is yes */
1476                                DOT_DLINES;
1477 #undef HANDLE_DLINE
1478                            }
1479 #undef H1
1480                            break;
1481                        case 2: /* 1 yes, 2 no */
1482                            dot_setall(sstate->state, i, j,
1483                                       LINE_UNKNOWN, LINE_YES);
1484                            dot_solved[i + j*(w+1)] = TRUE;
1485                            solver_progress = TRUE;
1486                            break;
1487                        case 3: /* 1 yes, 3 no */
1488                            FOUND_MISTAKE;
1489                            break;
1490                    }
1491                    break;
1492                case 2:
1493                    if (dot_setall(sstate->state, i, j, LINE_UNKNOWN, LINE_NO)) {
1494                        solver_progress = TRUE;
1495                    }
1496                    dot_solved[i + j*(w+1)] = TRUE;
1497                    break;
1498                case 3:
1499                case 4:
1500                    FOUND_MISTAKE;
1501                    break;
1502                }
1503                if (diff > DIFF_EASY) {
1504 #define HANDLE_DLINE(dline, dir1_dot, dir2_dot)                               \
1505                if (BIT_SET(sstate->dot_atleastone[i + (w + 1) * j], dline)) { \
1506                    solver_progress |=                                         \
1507                      SET_BIT(sstate->dot_atmostone[i + (w + 1) * j],          \
1508                              OPP_DLINE(dline));                               \
1509                }
1510                    /* If at least one of a dline in a dot is YES, at most one
1511                     * of the opposite dline to that dot must be YES. */
1512                    DOT_DLINES;
1513                }
1514 #undef HANDLE_DLINE
1515
1516 #define H1(dline, dir1_sq, dir2_sq, dot_howmany, line_query, line_set)        \
1517                if (BIT_SET(sstate->dot_howmany[i + (w+1) * j], dline)) {      \
1518                    t = dir1_sq(sstate->state, i, j);                          \
1519                    if (t == line_query) {                                     \
1520                        if (dir2_sq(sstate->state, i, j) != line_set) {        \
1521                            LV_##dir2_sq(sstate->state, i, j) = line_set;      \
1522                            solver_progress = TRUE;                            \
1523                        }                                                      \
1524                    } else {                                                   \
1525                        t = dir2_sq(sstate->state, i, j);                      \
1526                        if (t == line_query) {                                 \
1527                            if (dir1_sq(sstate->state, i, j) != line_set) {    \
1528                                LV_##dir1_sq(sstate->state, i, j) = line_set;  \
1529                                solver_progress = TRUE;                        \
1530                            }                                                  \
1531                        }                                                      \
1532                    }                                                          \
1533                }
1534                if (diff > DIFF_EASY) {
1535 #define HANDLE_DLINE(dline, dir1_sq, dir2_sq)                                 \
1536                H1(dline, dir1_sq, dir2_sq, dot_atmostone, LINE_YES, LINE_NO)
1537                    /* If at most one of the DLINE is on, and one is definitely
1538                     * on, set the other to definitely off */
1539                    DOT_DLINES;
1540 #undef HANDLE_DLINE
1541                }
1542
1543                if (diff > DIFF_EASY) {
1544 #define HANDLE_DLINE(dline, dir1_sq, dir2_sq)                                 \
1545                H1(dline, dir1_sq, dir2_sq, dot_atleastone, LINE_NO, LINE_YES)
1546                    /* If at least one of the DLINE is on, and one is definitely
1547                     * off, set the other to definitely on */
1548                    DOT_DLINES;
1549 #undef HANDLE_DLINE
1550                }
1551 #undef H1
1552
1553            }
1554        }
1555
1556        /* More obscure per-square operations */
1557        for (j = 0; j < h; ++j) {
1558            for (i = 0; i < w; ++i) {
1559                if (square_solved[i + j*w])
1560                    continue;
1561
1562                switch (CLUE_AT(sstate->state, i, j)) {
1563                    case '1':
1564                        if (diff > DIFF_EASY) {
1565 #define HANDLE_DLINE(dline, dir1_sq, dir2_sq, a, b)                          \
1566                        /* At most one of any DLINE can be set */             \
1567                        SET_BIT(sstate->dot_atmostone[i+a + (w + 1) * (j+b)], \
1568                                dline);                                       \
1569                        /* This DLINE provides enough YESes to solve the clue */\
1570                        if (BIT_SET(sstate->dot_atleastone                    \
1571                                       [i+a + (w + 1) * (j+b)],               \
1572                                    dline)) {                                 \
1573                            solver_progress |=                                \
1574                                dot_setall_dlines(sstate, OPP_DLINE(dline),   \
1575                                                  i+(1-a), j+(1-b),           \
1576                                                  LINE_UNKNOWN, LINE_NO);     \
1577                        }
1578                            SQUARE_DLINES;
1579 #undef HANDLE_DLINE
1580                        }
1581                        break;
1582                    case '2':
1583                        if (diff > DIFF_EASY) {
1584 #define H1(dline, dot_at1one, dot_at2one, a, b)                          \
1585                if (BIT_SET(sstate->dot_at1one                            \
1586                              [i+a + (w+1) * (j+b)], dline)) {            \
1587                    solver_progress |=                                    \
1588                      SET_BIT(sstate->dot_at2one                          \
1589                                [i+(1-a) + (w+1) * (j+(1-b))],            \
1590                              OPP_DLINE(dline));                          \
1591                }
1592 #define HANDLE_DLINE(dline, dir1_sq, dir2_sq, a, b)             \
1593             H1(dline, dot_atleastone, dot_atmostone, a, b);     \
1594             H1(dline, dot_atmostone, dot_atleastone, a, b);
1595                            /* If at least one of one DLINE is set, at most one
1596                             * of the opposing one is and vice versa */
1597                            SQUARE_DLINES;
1598                        }
1599 #undef HANDLE_DLINE
1600 #undef H1
1601                        break;
1602                    case '3':
1603                        if (diff > DIFF_EASY) {
1604 #define HANDLE_DLINE(dline, dir1_sq, dir2_sq, a, b)                           \
1605                        /* At least one of any DLINE can be set */             \
1606                        solver_progress |=                                     \
1607                            SET_BIT(sstate->dot_atleastone                     \
1608                                      [i+a + (w + 1) * (j+b)],                 \
1609                                    dline);                                    \
1610                        /* This DLINE provides enough NOs to solve the clue */ \
1611                        if (BIT_SET(sstate->dot_atmostone                      \
1612                                      [i+a + (w + 1) * (j+b)],                 \
1613                                    dline)) {                                  \
1614                            solver_progress |=                                 \
1615                                dot_setall_dlines(sstate, OPP_DLINE(dline),    \
1616                                                  i+(1-a), j+(1-b),            \
1617                                                  LINE_UNKNOWN, LINE_YES);     \
1618                        }
1619                            SQUARE_DLINES;
1620 #undef HANDLE_DLINE
1621                        }
1622                        break;
1623                }
1624            }
1625        }
1626
1627        if (!solver_progress) {
1628            int edgecount = 0, clues = 0, satclues = 0, sm1clues = 0;
1629            int shortest_chainlen = DOT_COUNT(sstate->state);
1630            int loop_found = FALSE;
1631            int d;
1632            int dots_connected;
1633
1634            /*
1635             * Go through the grid and update for all the new edges.
1636             * Since merge_dots() is idempotent, the simplest way to
1637             * do this is just to update for _all_ the edges.
1638             *
1639             * Also, while we're here, we count the edges, count the
1640             * clues, count the satisfied clues, and count the
1641             * satisfied-minus-one clues.
1642             */
1643            for (j = 0; j < h+1; ++j) {
1644                for (i = 0; i < w+1; ++i) {
1645                    if (RIGHTOF_DOT(sstate->state, i, j) == LINE_YES) {
1646                        loop_found |= merge_dots(sstate, i, j, i+1, j);
1647                        edgecount++;
1648                    }
1649                    if (BELOW_DOT(sstate->state, i, j) == LINE_YES) {
1650                        loop_found |= merge_dots(sstate, i, j, i, j+1);
1651                        edgecount++;
1652                    }
1653
1654                    if (CLUE_AT(sstate->state, i, j) != ' ') {
1655                        int c = CLUE_AT(sstate->state, i, j) - '0';
1656                        int o = square_order(sstate->state, i, j, LINE_YES);
1657                        if (o == c)
1658                            satclues++;
1659                        else if (o == c-1)
1660                            sm1clues++;
1661                        clues++;
1662                    }
1663                }
1664            }
1665
1666            for (i = 0; i < DOT_COUNT(sstate->state); ++i) {
1667                dots_connected = sstate->looplen[dsf_canonify(sstate->dotdsf,i)];
1668                if (dots_connected > 1)
1669                    shortest_chainlen = min(shortest_chainlen, dots_connected);
1670            }
1671
1672            assert(sstate->solver_status == SOLVER_INCOMPLETE);
1673
1674            if (satclues == clues && shortest_chainlen == edgecount) {
1675                sstate->solver_status = SOLVER_SOLVED;
1676                /* This discovery clearly counts as progress, even if we haven't
1677                 * just added any lines or anything */
1678                solver_progress = TRUE;
1679                goto finished_loop_checking;
1680            }
1681
1682            /*
1683             * Now go through looking for LINE_UNKNOWN edges which
1684             * connect two dots that are already in the same
1685             * equivalence class. If we find one, test to see if the
1686             * loop it would create is a solution.
1687             */
1688            for (j = 0; j <= h; ++j) {
1689                for (i = 0; i <= w; ++i) {
1690                    for (d = 0; d < 2; d++) {
1691                        int i2, j2, eqclass, val;
1692
1693                        if (d == 0) {
1694                            if (RIGHTOF_DOT(sstate->state, i, j) !=
1695                                LINE_UNKNOWN)
1696                                continue;
1697                            i2 = i+1;
1698                            j2 = j;
1699                        } else {
1700                            if (BELOW_DOT(sstate->state, i, j) !=
1701                                LINE_UNKNOWN)
1702                                continue;
1703                            i2 = i;
1704                            j2 = j+1;
1705                        }
1706
1707                        eqclass = dsf_canonify(sstate->dotdsf, j * (w+1) + i);
1708                        if (eqclass != dsf_canonify(sstate->dotdsf,
1709                                                    j2 * (w+1) + i2))
1710                            continue;
1711
1712                        val = LINE_NO;  /* loop is bad until proven otherwise */
1713
1714                        /*
1715                         * This edge would form a loop. Next
1716                         * question: how long would the loop be?
1717                         * Would it equal the total number of edges
1718                         * (plus the one we'd be adding if we added
1719                         * it)?
1720                         */
1721                        if (sstate->looplen[eqclass] == edgecount + 1) {
1722                            int sm1_nearby;
1723                            int cx, cy;
1724
1725                            /*
1726                             * This edge would form a loop which
1727                             * took in all the edges in the entire
1728                             * grid. So now we need to work out
1729                             * whether it would be a valid solution
1730                             * to the puzzle, which means we have to
1731                             * check if it satisfies all the clues.
1732                             * This means that every clue must be
1733                             * either satisfied or satisfied-minus-
1734                             * 1, and also that the number of
1735                             * satisfied-minus-1 clues must be at
1736                             * most two and they must lie on either
1737                             * side of this edge.
1738                             */
1739                            sm1_nearby = 0;
1740                            cx = i - (j2-j);
1741                            cy = j - (i2-i);
1742                            if (CLUE_AT(sstate->state, cx,cy) != ' ' &&
1743                                square_order(sstate->state, cx,cy, LINE_YES) ==
1744                                CLUE_AT(sstate->state, cx,cy) - '0' - 1)
1745                                sm1_nearby++;
1746                            if (CLUE_AT(sstate->state, i, j) != ' ' &&
1747                                square_order(sstate->state, i, j, LINE_YES) ==
1748                                CLUE_AT(sstate->state, i, j) - '0' - 1)
1749                                sm1_nearby++;
1750                            if (sm1clues == sm1_nearby &&
1751                                sm1clues + satclues == clues)
1752                                val = LINE_YES;  /* loop is good! */
1753                        }
1754
1755                        /*
1756                         * Right. Now we know that adding this edge
1757                         * would form a loop, and we know whether
1758                         * that loop would be a viable solution or
1759                         * not.
1760                         *
1761                         * If adding this edge produces a solution,
1762                         * then we know we've found _a_ solution but
1763                         * we don't know that it's _the_ solution -
1764                         * if it were provably the solution then
1765                         * we'd have deduced this edge some time ago
1766                         * without the need to do loop detection. So
1767                         * in this state we return SOLVER_AMBIGUOUS,
1768                         * which has the effect that hitting Solve
1769                         * on a user-provided puzzle will fill in a
1770                         * solution but using the solver to
1771                         * construct new puzzles won't consider this
1772                         * a reasonable deduction for the user to
1773                         * make.
1774                         */
1775                        if (d == 0) {
1776                            LV_RIGHTOF_DOT(sstate->state, i, j) = val;
1777                            solver_progress = TRUE;
1778                        } else {
1779                            LV_BELOW_DOT(sstate->state, i, j) = val;
1780                            solver_progress = TRUE;
1781                        }
1782                        if (val == LINE_YES) {
1783                            sstate->solver_status = SOLVER_AMBIGUOUS;
1784                            goto finished_loop_checking;
1785                        }
1786                    }
1787                }
1788            }
1789
1790            finished_loop_checking:
1791
1792            if (!solver_progress ||
1793                sstate->solver_status == SOLVER_SOLVED ||
1794                sstate->solver_status == SOLVER_AMBIGUOUS) {
1795                break;
1796            }
1797        }
1798    }
1799
1800    sfree(dot_solved); sfree(square_solved);
1801
1802    if (sstate->solver_status == SOLVER_SOLVED ||
1803        sstate->solver_status == SOLVER_AMBIGUOUS) {
1804        /* s/LINE_UNKNOWN/LINE_NO/g */
1805        array_setall(sstate->state->hl, LINE_UNKNOWN, LINE_NO,
1806                HL_COUNT(sstate->state));
1807        array_setall(sstate->state->vl, LINE_UNKNOWN, LINE_NO,
1808                VL_COUNT(sstate->state));
1809        return sstate;
1810    }
1811
1812    /* Perform recursive calls */
1813    if (sstate->recursion_remaining) {
1814        sstate_saved = dup_solver_state(sstate);
1815
1816        sstate->recursion_remaining--;
1817
1818        recursive_soln_count = 0;
1819        sstate_rec_solved = NULL;
1820
1821        /* Memory management:
1822         * sstate_saved won't be modified but needs to be freed when we have
1823         * finished with it.
1824         * sstate is expected to contain our 'best' solution by the time we
1825         * finish this section of code.  It's the thing we'll try adding lines
1826         * to, seeing if they make it more solvable.
1827         * If sstate_rec_solved is non-NULL, it will supersede sstate
1828         * eventually.  sstate_tmp should not hold a value persistently.
1829         */
1830
1831        /* NB SOLVER_AMBIGUOUS is like SOLVER_SOLVED except the solver is aware
1832         * of the possibility of additional solutions.  So as soon as we have a
1833         * SOLVER_AMBIGUOUS we can safely propagate it back to our caller, but
1834         * if we get a SOLVER_SOLVED we want to keep trying in case we find
1835         * further solutions and have to mark it ambiguous.
1836         */
1837
1838 #define DO_RECURSIVE_CALL(dir_dot)                                         \
1839        if (dir_dot(sstate->state, i, j) == LINE_UNKNOWN) {                 \
1840            debug(("Trying " #dir_dot " at [%d,%d]\n", i, j));               \
1841            LV_##dir_dot(sstate->state, i, j) = LINE_YES;                   \
1842            sstate_tmp = solve_game_rec(sstate, diff);                      \
1843            switch (sstate_tmp->solver_status) {                            \
1844                case SOLVER_AMBIGUOUS:                                      \
1845                    debug(("Solver ambiguous, returning\n"));                \
1846                    sstate_rec_solved = sstate_tmp;                         \
1847                    goto finished_recursion;                                \
1848                case SOLVER_SOLVED:                                         \
1849                    switch (++recursive_soln_count) {                       \
1850                        case 1:                                             \
1851                            debug(("One solution found\n"));                 \
1852                            sstate_rec_solved = sstate_tmp;                 \
1853                            break;                                          \
1854                        case 2:                                             \
1855                            debug(("Ambiguous solutions found\n"));          \
1856                            free_solver_state(sstate_tmp);                  \
1857                            sstate_rec_solved->solver_status = SOLVER_AMBIGUOUS;\
1858                            goto finished_recursion;                        \
1859                        default:                                            \
1860                            assert(!"recursive_soln_count out of range");   \
1861                            break;                                          \
1862                    }                                                       \
1863                    break;                                                  \
1864                case SOLVER_MISTAKE:                                        \
1865                    debug(("Non-solution found\n"));                         \
1866                    free_solver_state(sstate_tmp);                          \
1867                    free_solver_state(sstate_saved);                        \
1868                    LV_##dir_dot(sstate->state, i, j) = LINE_NO;            \
1869                    goto nonrecursive_solver;                               \
1870                case SOLVER_INCOMPLETE:                                     \
1871                    debug(("Recursive step inconclusive\n"));                \
1872                    free_solver_state(sstate_tmp);                          \
1873                    break;                                                  \
1874            }                                                               \
1875            free_solver_state(sstate);                                      \
1876            sstate = dup_solver_state(sstate_saved);                        \
1877        }
1878
1879        for (j = 0; j < h + 1; ++j) {
1880            for (i = 0; i < w + 1; ++i) {
1881                /* Only perform recursive calls on 'loose ends' */
1882                if (dot_order(sstate->state, i, j, LINE_YES) == 1) {
1883                    DO_RECURSIVE_CALL(LEFTOF_DOT);
1884                    DO_RECURSIVE_CALL(RIGHTOF_DOT);
1885                    DO_RECURSIVE_CALL(ABOVE_DOT);
1886                    DO_RECURSIVE_CALL(BELOW_DOT);
1887                }
1888            }
1889        }
1890
1891 finished_recursion:
1892
1893        if (sstate_rec_solved) {
1894            free_solver_state(sstate);
1895            sstate = sstate_rec_solved;
1896        }
1897    }
1898
1899    return sstate;
1900 }
1901
1902 /* XXX bits of solver that may come in handy one day */
1903 #if 0
1904 #define HANDLE_DLINE(dline, dir1_dot, dir2_dot)                         \
1905                    /* dline from this dot that's entirely unknown must have
1906                     * both lines identical */                           \
1907                    if (dir1_dot(sstate->state, i, j) == LINE_UNKNOWN &&       \
1908                        dir2_dot(sstate->state, i, j) == LINE_UNKNOWN) {       \
1909                        sstate->dline_identical[i + (sstate->state->w + 1) * j] |= \
1910                            1<<dline;                                    \
1911                    } else if (sstate->dline_identical[i +
1912                                                       (sstate->state->w + 1) * j] &\
1913                               1<<dline) {                                   \
1914                        /* If they're identical and one is known do the obvious
1915                         * thing */                                      \
1916                        t = dir1_dot(sstate->state, i, j);                     \
1917                        if (t != LINE_UNKNOWN)                           \
1918                            dir2_dot(sstate->state, i, j) = t;                 \
1919                        else {                                           \
1920                            t = dir2_dot(sstate->state, i, j);                 \
1921                            if (t != LINE_UNKNOWN)                       \
1922                                dir1_dot(sstate->state, i, j) = t;             \
1923                        }                                                \
1924                    }                                                    \
1925                    DOT_DLINES;
1926 #undef HANDLE_DLINE
1927 #endif
1928
1929 #if 0
1930 #define HANDLE_DLINE(dline, dir1_sq, dir2_sq, a, b) \
1931                        if (sstate->dline_identical[i+a +                     \
1932                                                    (sstate->state->w + 1) * (j+b)] &\
1933                            1<<dline) {                                       \
1934                            dir1_sq(sstate->state, i, j) = LINE_YES;                \
1935                            dir2_sq(sstate->state, i, j) = LINE_YES;                \
1936                        }
1937                        /* If two lines are the same they must be on */
1938                        SQUARE_DLINES;
1939 #undef HANDLE_DLINE
1940 #endif
1941
1942
1943 #if 0
1944 #define HANDLE_DLINE(dline, dir1_sq, dir2_sq, a, b) \
1945                if (sstate->dot_atmostone[i+a + (sstate->state->w + 1) * (j+b)] &  \
1946                    1<<dline) {                                   \
1947                    if (square_order(sstate->state, i, j,  LINE_UNKNOWN) - 1 ==  \
1948                        CLUE_AT(sstate->state, i, j) - '0') {      \
1949                        square_setall(sstate->state, i, j, LINE_UNKNOWN, LINE_YES); \
1950                            /* XXX the following may overwrite known data! */ \
1951                        dir1_sq(sstate->state, i, j) = LINE_UNKNOWN;  \
1952                        dir2_sq(sstate->state, i, j) = LINE_UNKNOWN;  \
1953                    }                                  \
1954                }
1955                SQUARE_DLINES;
1956 #undef HANDLE_DLINE
1957 #endif
1958
1959 #if 0
1960 #define HANDLE_DLINE(dline, dir1_sq, dir2_sq, a, b) \
1961                        if (sstate->dline_identical[i+a +
1962                                                    (sstate->state->w + 1) * (j+b)] &\
1963                            1<<dline) {                                       \
1964                            dir1_sq(sstate->state, i, j) = LINE_NO;                 \
1965                            dir2_sq(sstate->state, i, j) = LINE_NO;                 \
1966                        }
1967                        /* If two lines are the same they must be off */
1968                        SQUARE_DLINES;
1969 #undef HANDLE_DLINE
1970 #endif
1971
1972 static char *solve_game(game_state *state, game_state *currstate,
1973                         char *aux, char **error)
1974 {
1975     char *soln = NULL;
1976     solver_state *sstate, *new_sstate;
1977
1978     sstate = new_solver_state(state);
1979     new_sstate = solve_game_rec(sstate, DIFFCOUNT);
1980
1981     if (new_sstate->solver_status == SOLVER_SOLVED) {
1982         soln = encode_solve_move(new_sstate->state);
1983     } else if (new_sstate->solver_status == SOLVER_AMBIGUOUS) {
1984         soln = encode_solve_move(new_sstate->state);
1985         /**error = "Solver found ambiguous solutions"; */
1986     } else {
1987         soln = encode_solve_move(new_sstate->state);
1988         /**error = "Solver failed"; */
1989     }
1990
1991     free_solver_state(new_sstate);
1992     free_solver_state(sstate);
1993
1994     return soln;
1995 }
1996
1997 static char *game_text_format(game_state *state)
1998 {
1999     int i, j;
2000     int len;
2001     char *ret, *rp;
2002
2003     len = (2 * state->w + 2) * (2 * state->h + 1);
2004     rp = ret = snewn(len + 1, char);
2005
2006 #define DRAW_HL                          \
2007     switch (ABOVE_SQUARE(state, i, j)) { \
2008         case LINE_YES:                   \
2009             rp += sprintf(rp, " -");     \
2010             break;                       \
2011         case LINE_NO:                    \
2012             rp += sprintf(rp, " x");     \
2013             break;                       \
2014         case LINE_UNKNOWN:               \
2015             rp += sprintf(rp, "  ");     \
2016             break;                       \
2017         default:                         \
2018             assert(!"Illegal line state for HL");\
2019     }
2020
2021 #define DRAW_VL                          \
2022     switch (LEFTOF_SQUARE(state, i, j)) {\
2023         case LINE_YES:                   \
2024             rp += sprintf(rp, "|");      \
2025             break;                       \
2026         case LINE_NO:                    \
2027             rp += sprintf(rp, "x");      \
2028             break;                       \
2029         case LINE_UNKNOWN:               \
2030             rp += sprintf(rp, " ");      \
2031             break;                       \
2032         default:                         \
2033             assert(!"Illegal line state for VL");\
2034     }
2035
2036     for (j = 0; j < state->h; ++j) {
2037         for (i = 0; i < state->w; ++i) {
2038             DRAW_HL;
2039         }
2040         rp += sprintf(rp, " \n");
2041         for (i = 0; i < state->w; ++i) {
2042             DRAW_VL;
2043             rp += sprintf(rp, "%c", (int)(CLUE_AT(state, i, j)));
2044         }
2045         DRAW_VL;
2046         rp += sprintf(rp, "\n");
2047     }
2048     for (i = 0; i < state->w; ++i) {
2049         DRAW_HL;
2050     }
2051     rp += sprintf(rp, " \n");
2052
2053     assert(strlen(ret) == len);
2054     return ret;
2055 }
2056
2057 static game_ui *new_ui(game_state *state)
2058 {
2059     return NULL;
2060 }
2061
2062 static void free_ui(game_ui *ui)
2063 {
2064 }
2065
2066 static char *encode_ui(game_ui *ui)
2067 {
2068     return NULL;
2069 }
2070
2071 static void decode_ui(game_ui *ui, char *encoding)
2072 {
2073 }
2074
2075 static void game_changed_state(game_ui *ui, game_state *oldstate,
2076                                game_state *newstate)
2077 {
2078 }
2079
2080 struct game_drawstate {
2081     int started;
2082     int tilesize, linewidth;
2083     int flashing;
2084     char *hl, *vl;
2085     char *clue_error;
2086 };
2087
2088 static char *interpret_move(game_state *state, game_ui *ui, game_drawstate *ds,
2089                             int x, int y, int button)
2090 {
2091     int hl_selected;
2092     int i, j, p, q;
2093     char *ret, buf[80];
2094     char button_char = ' ';
2095     enum line_state old_state;
2096
2097     button &= ~MOD_MASK;
2098
2099     /* Around each line is a diamond-shaped region where points within that
2100      * region are closer to this line than any other.  We assume any click
2101      * within a line's diamond was meant for that line.  It would all be a lot
2102      * simpler if the / and % operators respected modulo arithmetic properly
2103      * for negative numbers. */
2104
2105     x -= BORDER;
2106     y -= BORDER;
2107
2108     /* Get the coordinates of the square the click was in */
2109     i = (x + TILE_SIZE) / TILE_SIZE - 1;
2110     j = (y + TILE_SIZE) / TILE_SIZE - 1;
2111
2112     /* Get the precise position inside square [i,j] */
2113     p = (x + TILE_SIZE) % TILE_SIZE;
2114     q = (y + TILE_SIZE) % TILE_SIZE;
2115
2116     /* After this bit of magic [i,j] will correspond to the point either above
2117      * or to the left of the line selected */
2118     if (p > q) {
2119         if (TILE_SIZE - p > q) {
2120             hl_selected = TRUE;
2121         } else {
2122             hl_selected = FALSE;
2123             ++i;
2124         }
2125     } else {
2126         if (TILE_SIZE - q > p) {
2127             hl_selected = FALSE;
2128         } else {
2129             hl_selected = TRUE;
2130             ++j;
2131         }
2132     }
2133
2134     if (i < 0 || j < 0)
2135         return NULL;
2136
2137     if (hl_selected) {
2138         if (i >= state->w || j >= state->h + 1)
2139             return NULL;
2140     } else {
2141         if (i >= state->w + 1 || j >= state->h)
2142             return NULL;
2143     }
2144
2145     /* I think it's only possible to play this game with mouse clicks, sorry */
2146     /* Maybe will add mouse drag support some time */
2147     if (hl_selected)
2148         old_state = RIGHTOF_DOT(state, i, j);
2149     else
2150         old_state = BELOW_DOT(state, i, j);
2151
2152     switch (button) {
2153         case LEFT_BUTTON:
2154             switch (old_state) {
2155                 case LINE_UNKNOWN:
2156                     button_char = 'y';
2157                     break;
2158                 case LINE_YES:
2159                 case LINE_NO:
2160                     button_char = 'u';
2161                     break;
2162             }
2163             break;
2164         case MIDDLE_BUTTON:
2165             button_char = 'u';
2166             break;
2167         case RIGHT_BUTTON:
2168             switch (old_state) {
2169                 case LINE_UNKNOWN:
2170                     button_char = 'n';
2171                     break;
2172                 case LINE_NO:
2173                 case LINE_YES:
2174                     button_char = 'u';
2175                     break;
2176             }
2177             break;
2178         default:
2179             return NULL;
2180     }
2181
2182
2183     sprintf(buf, "%d,%d%c%c", i, j, (int)(hl_selected ? 'h' : 'v'), (int)button_char);
2184     ret = dupstr(buf);
2185
2186     return ret;
2187 }
2188
2189 static game_state *execute_move(game_state *state, char *move)
2190 {
2191     int i, j;
2192     game_state *newstate = dup_game(state);
2193
2194     if (move[0] == 'S') {
2195         move++;
2196         newstate->cheated = TRUE;
2197     }
2198
2199     while (*move) {
2200         i = atoi(move);
2201         move = strchr(move, ',');
2202         if (!move)
2203             goto fail;
2204         j = atoi(++move);
2205         move += strspn(move, "1234567890");
2206         switch (*(move++)) {
2207             case 'h':
2208                 if (i >= newstate->w || j > newstate->h)
2209                     goto fail;
2210                 switch (*(move++)) {
2211                     case 'y':
2212                         LV_RIGHTOF_DOT(newstate, i, j) = LINE_YES;
2213                         break;
2214                     case 'n':
2215                         LV_RIGHTOF_DOT(newstate, i, j) = LINE_NO;
2216                         break;
2217                     case 'u':
2218                         LV_RIGHTOF_DOT(newstate, i, j) = LINE_UNKNOWN;
2219                         break;
2220                     default:
2221                         goto fail;
2222                 }
2223                 break;
2224             case 'v':
2225                 if (i > newstate->w || j >= newstate->h)
2226                     goto fail;
2227                 switch (*(move++)) {
2228                     case 'y':
2229                         LV_BELOW_DOT(newstate, i, j) = LINE_YES;
2230                         break;
2231                     case 'n':
2232                         LV_BELOW_DOT(newstate, i, j) = LINE_NO;
2233                         break;
2234                     case 'u':
2235                         LV_BELOW_DOT(newstate, i, j) = LINE_UNKNOWN;
2236                         break;
2237                     default:
2238                         goto fail;
2239                 }
2240                 break;
2241             default:
2242                 goto fail;
2243         }
2244     }
2245
2246     /*
2247      * Check for completion.
2248      */
2249     i = 0;                             /* placate optimiser */
2250     for (j = 0; j <= newstate->h; j++) {
2251         for (i = 0; i < newstate->w; i++)
2252             if (LV_RIGHTOF_DOT(newstate, i, j) == LINE_YES)
2253                 break;
2254         if (i < newstate->w)
2255             break;
2256     }
2257     if (j <= newstate->h) {
2258         int prevdir = 'R';
2259         int x = i, y = j;
2260         int looplen, count;
2261
2262         /*
2263          * We've found a horizontal edge at (i,j). Follow it round
2264          * to see if it's part of a loop.
2265          */
2266         looplen = 0;
2267         while (1) {
2268             int order = dot_order(newstate, x, y, LINE_YES);
2269             if (order != 2)
2270                 goto completion_check_done;
2271
2272             if (LEFTOF_DOT(newstate, x, y) == LINE_YES && prevdir != 'L') {
2273                 x--;
2274                 prevdir = 'R';
2275             } else if (RIGHTOF_DOT(newstate, x, y) == LINE_YES &&
2276                        prevdir != 'R') {
2277                 x++;
2278                 prevdir = 'L';
2279             } else if (ABOVE_DOT(newstate, x, y) == LINE_YES &&
2280                        prevdir != 'U') {
2281                 y--;
2282                 prevdir = 'D';
2283             } else if (BELOW_DOT(newstate, x, y) == LINE_YES &&
2284                        prevdir != 'D') {
2285                 y++;
2286                 prevdir = 'U';
2287             } else {
2288                 assert(!"Can't happen");   /* dot_order guarantees success */
2289             }
2290
2291             looplen++;
2292
2293             if (x == i && y == j)
2294                 break;
2295         }
2296
2297         if (x != i || y != j || looplen == 0)
2298             goto completion_check_done;
2299
2300         /*
2301          * We've traced our way round a loop, and we know how many
2302          * line segments were involved. Count _all_ the line
2303          * segments in the grid, to see if the loop includes them
2304          * all.
2305          */
2306         count = 0;
2307         for (j = 0; j <= newstate->h; j++)
2308             for (i = 0; i <= newstate->w; i++)
2309                 count += ((RIGHTOF_DOT(newstate, i, j) == LINE_YES) +
2310                           (BELOW_DOT(newstate, i, j) == LINE_YES));
2311         assert(count >= looplen);
2312         if (count != looplen)
2313             goto completion_check_done;
2314
2315         /*
2316          * The grid contains one closed loop and nothing else.
2317          * Check that all the clues are satisfied.
2318          */
2319         for (j = 0; j < newstate->h; ++j) {
2320             for (i = 0; i < newstate->w; ++i) {
2321                 int n = CLUE_AT(newstate, i, j);
2322                 if (n != ' ') {
2323                     if (square_order(newstate, i, j, LINE_YES) != n - '0') {
2324                         goto completion_check_done;
2325                     }
2326                 }
2327             }
2328         }
2329
2330         /*
2331          * Completed!
2332          */
2333         newstate->solved = TRUE;
2334     }
2335
2336 completion_check_done:
2337     return newstate;
2338
2339 fail:
2340     free_game(newstate);
2341     return NULL;
2342 }
2343
2344 /* ----------------------------------------------------------------------
2345  * Drawing routines.
2346  */
2347
2348 #define SIZE(d) ((d) * TILE_SIZE + 2 * BORDER + 1)
2349
2350 static void game_compute_size(game_params *params, int tilesize,
2351                               int *x, int *y)
2352 {
2353     struct { int tilesize; } ads, *ds = &ads;
2354     ads.tilesize = tilesize;
2355
2356     *x = SIZE(params->w);
2357     *y = SIZE(params->h);
2358 }
2359
2360 static void game_set_size(drawing *dr, game_drawstate *ds,
2361                           game_params *params, int tilesize)
2362 {
2363     ds->tilesize = tilesize;
2364     ds->linewidth = max(1,tilesize/16);
2365 }
2366
2367 static float *game_colours(frontend *fe, int *ncolours)
2368 {
2369     float *ret = snewn(4 * NCOLOURS, float);
2370
2371     frontend_default_colour(fe, &ret[COL_BACKGROUND * 3]);
2372
2373     ret[COL_FOREGROUND * 3 + 0] = 0.0F;
2374     ret[COL_FOREGROUND * 3 + 1] = 0.0F;
2375     ret[COL_FOREGROUND * 3 + 2] = 0.0F;
2376
2377     ret[COL_HIGHLIGHT * 3 + 0] = 1.0F;
2378     ret[COL_HIGHLIGHT * 3 + 1] = 1.0F;
2379     ret[COL_HIGHLIGHT * 3 + 2] = 1.0F;
2380
2381     ret[COL_MISTAKE * 3 + 0] = 1.0F;
2382     ret[COL_MISTAKE * 3 + 1] = 0.0F;
2383     ret[COL_MISTAKE * 3 + 2] = 0.0F;
2384
2385     *ncolours = NCOLOURS;
2386     return ret;
2387 }
2388
2389 static game_drawstate *game_new_drawstate(drawing *dr, game_state *state)
2390 {
2391     struct game_drawstate *ds = snew(struct game_drawstate);
2392
2393     ds->tilesize = ds->linewidth = 0;
2394     ds->started = 0;
2395     ds->hl = snewn(HL_COUNT(state), char);
2396     ds->vl = snewn(VL_COUNT(state), char);
2397     ds->clue_error = snewn(SQUARE_COUNT(state), char);
2398     ds->flashing = 0;
2399
2400     memset(ds->hl, LINE_UNKNOWN, HL_COUNT(state));
2401     memset(ds->vl, LINE_UNKNOWN, VL_COUNT(state));
2402     memset(ds->clue_error, 0, SQUARE_COUNT(state));
2403
2404     return ds;
2405 }
2406
2407 static void game_free_drawstate(drawing *dr, game_drawstate *ds)
2408 {
2409     sfree(ds->clue_error);
2410     sfree(ds->hl);
2411     sfree(ds->vl);
2412     sfree(ds);
2413 }
2414
2415 static void game_redraw(drawing *dr, game_drawstate *ds, game_state *oldstate,
2416                         game_state *state, int dir, game_ui *ui,
2417                         float animtime, float flashtime)
2418 {
2419     int i, j, n;
2420     int w = state->w, h = state->h;
2421     char c[2];
2422     int line_colour, flash_changed;
2423     int clue_mistake;
2424
2425     if (!ds->started) {
2426         /*
2427          * The initial contents of the window are not guaranteed and
2428          * can vary with front ends. To be on the safe side, all games
2429          * should start by drawing a big background-colour rectangle
2430          * covering the whole window.
2431          */
2432         draw_rect(dr, 0, 0, SIZE(state->w), SIZE(state->h), COL_BACKGROUND);
2433
2434         /* Draw dots */
2435         for (j = 0; j < h + 1; ++j) {
2436             for (i = 0; i < w + 1; ++i) {
2437                 draw_rect(dr,
2438                           BORDER + i * TILE_SIZE - LINEWIDTH/2,
2439                           BORDER + j * TILE_SIZE - LINEWIDTH/2,
2440                           LINEWIDTH, LINEWIDTH, COL_FOREGROUND);
2441             }
2442         }
2443
2444         /* Draw clues */
2445         for (j = 0; j < h; ++j) {
2446             for (i = 0; i < w; ++i) {
2447                 c[0] = CLUE_AT(state, i, j);
2448                 c[1] = '\0';
2449                 draw_text(dr,
2450                           BORDER + i * TILE_SIZE + TILE_SIZE/2,
2451                           BORDER + j * TILE_SIZE + TILE_SIZE/2,
2452                           FONT_VARIABLE, TILE_SIZE/2,
2453                           ALIGN_VCENTRE | ALIGN_HCENTRE, COL_FOREGROUND, c);
2454             }
2455         }
2456         draw_update(dr, 0, 0,
2457                     state->w * TILE_SIZE + 2*BORDER + 1,
2458                     state->h * TILE_SIZE + 2*BORDER + 1);
2459         ds->started = TRUE;
2460     }
2461
2462     if (flashtime > 0 &&
2463         (flashtime <= FLASH_TIME/3 ||
2464          flashtime >= FLASH_TIME*2/3)) {
2465         flash_changed = !ds->flashing;
2466         ds->flashing = TRUE;
2467         line_colour = COL_HIGHLIGHT;
2468     } else {
2469         flash_changed = ds->flashing;
2470         ds->flashing = FALSE;
2471         line_colour = COL_FOREGROUND;
2472     }
2473
2474 #define CROSS_SIZE (3 * LINEWIDTH / 2)
2475
2476     /* Redraw clue colours if necessary */
2477     for (j = 0; j < h; ++j) {
2478         for (i = 0; i < w; ++i) {
2479             c[0] = CLUE_AT(state, i, j);
2480             c[1] = '\0';
2481             if (c[0] == ' ')
2482                 continue;
2483
2484             n = c[0] - '0';
2485             assert(n >= 0 && n <= 4);
2486
2487             clue_mistake = (square_order(state, i, j, LINE_YES) > n     ||
2488                             square_order(state, i, j, LINE_NO ) > (4-n));
2489
2490             if (clue_mistake != ds->clue_error[j * w + i]) {
2491                 draw_rect(dr,
2492                           BORDER + i * TILE_SIZE + CROSS_SIZE,
2493                           BORDER + j * TILE_SIZE + CROSS_SIZE,
2494                           TILE_SIZE - CROSS_SIZE * 2, TILE_SIZE - CROSS_SIZE * 2,
2495                           COL_BACKGROUND);
2496                 draw_text(dr,
2497                           BORDER + i * TILE_SIZE + TILE_SIZE/2,
2498                           BORDER + j * TILE_SIZE + TILE_SIZE/2,
2499                           FONT_VARIABLE, TILE_SIZE/2,
2500                           ALIGN_VCENTRE | ALIGN_HCENTRE,
2501                           clue_mistake ? COL_MISTAKE : COL_FOREGROUND, c);
2502                 draw_update(dr, i * TILE_SIZE + BORDER, j * TILE_SIZE + BORDER,
2503                             TILE_SIZE, TILE_SIZE);
2504
2505                 ds->clue_error[j * w + i] = clue_mistake;
2506             }
2507         }
2508     }
2509
2510     /* I've also had a request to colour lines red if they make a non-solution
2511      * loop, or if more than two lines go into any point.  I think that would
2512      * be good some time. */
2513
2514 #define CLEAR_VL(i, j) do {                                                \
2515                            draw_rect(dr,                                   \
2516                                  BORDER + i * TILE_SIZE - CROSS_SIZE,      \
2517                                  BORDER + j * TILE_SIZE + LINEWIDTH - LINEWIDTH/2,     \
2518                                  CROSS_SIZE * 2,                           \
2519                                  TILE_SIZE - LINEWIDTH,                    \
2520                                  COL_BACKGROUND);                          \
2521                            draw_update(dr,                                 \
2522                                        BORDER + i * TILE_SIZE - CROSS_SIZE, \
2523                                        BORDER + j * TILE_SIZE - CROSS_SIZE, \
2524                                        CROSS_SIZE*2,                       \
2525                                        TILE_SIZE + CROSS_SIZE*2);          \
2526                         } while (0)
2527
2528 #define CLEAR_HL(i, j) do {                                                \
2529                            draw_rect(dr,                                   \
2530                                  BORDER + i * TILE_SIZE + LINEWIDTH - LINEWIDTH/2,     \
2531                                  BORDER + j * TILE_SIZE - CROSS_SIZE,      \
2532                                  TILE_SIZE - LINEWIDTH,                    \
2533                                  CROSS_SIZE * 2,                           \
2534                                  COL_BACKGROUND);                          \
2535                            draw_update(dr,                                 \
2536                                        BORDER + i * TILE_SIZE - CROSS_SIZE, \
2537                                        BORDER + j * TILE_SIZE - CROSS_SIZE, \
2538                                        TILE_SIZE + CROSS_SIZE*2,           \
2539                                        CROSS_SIZE*2);                      \
2540                         } while (0)
2541
2542     /* Vertical lines */
2543     for (j = 0; j < h; ++j) {
2544         for (i = 0; i < w + 1; ++i) {
2545             switch (BELOW_DOT(state, i, j)) {
2546                 case LINE_UNKNOWN:
2547                     if (ds->vl[i + (w + 1) * j] != BELOW_DOT(state, i, j)) {
2548                         CLEAR_VL(i, j);
2549                     }
2550                     break;
2551                 case LINE_YES:
2552                     if (ds->vl[i + (w + 1) * j] != BELOW_DOT(state, i, j) ||
2553                         flash_changed) {
2554                         CLEAR_VL(i, j);
2555                         draw_rect(dr,
2556                                   BORDER + i * TILE_SIZE - LINEWIDTH/2,
2557                                   BORDER + j * TILE_SIZE + LINEWIDTH - LINEWIDTH/2,
2558                                   LINEWIDTH, TILE_SIZE - LINEWIDTH,
2559                                   line_colour);
2560                     }
2561                     break;
2562                 case LINE_NO:
2563                     if (ds->vl[i + (w + 1) * j] != BELOW_DOT(state, i, j)) {
2564                         CLEAR_VL(i, j);
2565                         draw_line(dr,
2566                                  BORDER + i * TILE_SIZE - CROSS_SIZE,
2567                                  BORDER + j * TILE_SIZE + TILE_SIZE/2 - CROSS_SIZE,
2568                                  BORDER + i * TILE_SIZE + CROSS_SIZE - 1,
2569                                  BORDER + j * TILE_SIZE + TILE_SIZE/2 + CROSS_SIZE - 1,
2570                                   COL_FOREGROUND);
2571                         draw_line(dr,
2572                                  BORDER + i * TILE_SIZE + CROSS_SIZE - 1,
2573                                  BORDER + j * TILE_SIZE + TILE_SIZE/2 - CROSS_SIZE,
2574                                  BORDER + i * TILE_SIZE - CROSS_SIZE,
2575                                  BORDER + j * TILE_SIZE + TILE_SIZE/2 + CROSS_SIZE - 1,
2576                                   COL_FOREGROUND);
2577                     }
2578                     break;
2579             }
2580             ds->vl[i + (w + 1) * j] = BELOW_DOT(state, i, j);
2581         }
2582     }
2583
2584     /* Horizontal lines */
2585     for (j = 0; j < h + 1; ++j) {
2586         for (i = 0; i < w; ++i) {
2587             switch (RIGHTOF_DOT(state, i, j)) {
2588                 case LINE_UNKNOWN:
2589                     if (ds->hl[i + w * j] != RIGHTOF_DOT(state, i, j)) {
2590                         CLEAR_HL(i, j);
2591                 }
2592                         break;
2593                 case LINE_YES:
2594                     if (ds->hl[i + w * j] != RIGHTOF_DOT(state, i, j) ||
2595                         flash_changed) {
2596                         CLEAR_HL(i, j);
2597                         draw_rect(dr,
2598                                   BORDER + i * TILE_SIZE + LINEWIDTH - LINEWIDTH/2,
2599                                   BORDER + j * TILE_SIZE - LINEWIDTH/2,
2600                                   TILE_SIZE - LINEWIDTH, LINEWIDTH,
2601                                   line_colour);
2602                         break;
2603                     }
2604                 case LINE_NO:
2605                     if (ds->hl[i + w * j] != RIGHTOF_DOT(state, i, j)) {
2606                         CLEAR_HL(i, j);
2607                         draw_line(dr,
2608                                  BORDER + i * TILE_SIZE + TILE_SIZE/2 - CROSS_SIZE,
2609                                  BORDER + j * TILE_SIZE + CROSS_SIZE - 1,
2610                                  BORDER + i * TILE_SIZE + TILE_SIZE/2 + CROSS_SIZE - 1,
2611                                  BORDER + j * TILE_SIZE - CROSS_SIZE,
2612                                   COL_FOREGROUND);
2613                         draw_line(dr,
2614                                  BORDER + i * TILE_SIZE + TILE_SIZE/2 - CROSS_SIZE,
2615                                  BORDER + j * TILE_SIZE - CROSS_SIZE,
2616                                  BORDER + i * TILE_SIZE + TILE_SIZE/2 + CROSS_SIZE - 1,
2617                                  BORDER + j * TILE_SIZE + CROSS_SIZE - 1,
2618                                   COL_FOREGROUND);
2619                         break;
2620                     }
2621             }
2622             ds->hl[i + w * j] = RIGHTOF_DOT(state, i, j);
2623         }
2624     }
2625 }
2626
2627 static float game_anim_length(game_state *oldstate, game_state *newstate,
2628                               int dir, game_ui *ui)
2629 {
2630     return 0.0F;
2631 }
2632
2633 static float game_flash_length(game_state *oldstate, game_state *newstate,
2634                                int dir, game_ui *ui)
2635 {
2636     if (!oldstate->solved  &&  newstate->solved &&
2637         !oldstate->cheated && !newstate->cheated) {
2638         return FLASH_TIME;
2639     }
2640
2641     return 0.0F;
2642 }
2643
2644 static int game_timing_state(game_state *state, game_ui *ui)
2645 {
2646     return TRUE;
2647 }
2648
2649 static void game_print_size(game_params *params, float *x, float *y)
2650 {
2651     int pw, ph;
2652
2653     /*
2654      * I'll use 7mm squares by default.
2655      */
2656     game_compute_size(params, 700, &pw, &ph);
2657     *x = pw / 100.0F;
2658     *y = ph / 100.0F;
2659 }
2660
2661 static void game_print(drawing *dr, game_state *state, int tilesize)
2662 {
2663     int w = state->w, h = state->h;
2664     int ink = print_mono_colour(dr, 0);
2665     int x, y;
2666     game_drawstate ads, *ds = &ads;
2667
2668     game_set_size(dr, ds, NULL, tilesize);
2669
2670     /*
2671      * Dots. I'll deliberately make the dots a bit wider than the
2672      * lines, so you can still see them. (And also because it's
2673      * annoyingly tricky to make them _exactly_ the same size...)
2674      */
2675     for (y = 0; y <= h; y++)
2676         for (x = 0; x <= w; x++)
2677             draw_circle(dr, BORDER + x * TILE_SIZE, BORDER + y * TILE_SIZE,
2678                         LINEWIDTH, ink, ink);
2679
2680     /*
2681      * Clues.
2682      */
2683     for (y = 0; y < h; y++)
2684         for (x = 0; x < w; x++)
2685             if (CLUE_AT(state, x, y) != ' ') {
2686                 char c[2];
2687
2688                 c[0] = CLUE_AT(state, x, y);
2689                 c[1] = '\0';
2690                 draw_text(dr,
2691                           BORDER + x * TILE_SIZE + TILE_SIZE/2,
2692                           BORDER + y * TILE_SIZE + TILE_SIZE/2,
2693                           FONT_VARIABLE, TILE_SIZE/2,
2694                           ALIGN_VCENTRE | ALIGN_HCENTRE, ink, c);
2695             }
2696
2697     /*
2698      * Lines. (At the moment, I'm not bothering with crosses.)
2699      */
2700     for (y = 0; y <= h; y++)
2701         for (x = 0; x < w; x++)
2702             if (RIGHTOF_DOT(state, x, y) == LINE_YES)
2703                 draw_rect(dr, BORDER + x * TILE_SIZE,
2704                           BORDER + y * TILE_SIZE - LINEWIDTH/2,
2705                           TILE_SIZE, (LINEWIDTH/2) * 2 + 1, ink);
2706     for (y = 0; y < h; y++)
2707         for (x = 0; x <= w; x++)
2708             if (BELOW_DOT(state, x, y) == LINE_YES)
2709                 draw_rect(dr, BORDER + x * TILE_SIZE - LINEWIDTH/2,
2710                           BORDER + y * TILE_SIZE,
2711                           (LINEWIDTH/2) * 2 + 1, TILE_SIZE, ink);
2712 }
2713
2714 #ifdef COMBINED
2715 #define thegame loopy
2716 #endif
2717
2718 const struct game thegame = {
2719     "Loopy", "games.loopy",
2720     default_params,
2721     game_fetch_preset,
2722     decode_params,
2723     encode_params,
2724     free_params,
2725     dup_params,
2726     TRUE, game_configure, custom_params,
2727     validate_params,
2728     new_game_desc,
2729     validate_desc,
2730     new_game,
2731     dup_game,
2732     free_game,
2733     1, solve_game,
2734     TRUE, game_text_format,
2735     new_ui,
2736     free_ui,
2737     encode_ui,
2738     decode_ui,
2739     game_changed_state,
2740     interpret_move,
2741     execute_move,
2742     PREFERRED_TILE_SIZE, game_compute_size, game_set_size,
2743     game_colours,
2744     game_new_drawstate,
2745     game_free_drawstate,
2746     game_redraw,
2747     game_anim_length,
2748     game_flash_length,
2749     TRUE, FALSE, game_print_size, game_print,
2750     FALSE,                             /* wants_statusbar */
2751     FALSE, game_timing_state,
2752     0,                                 /* flags */
2753 };