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  */
  46
  47 #include <stdio.h>
  48 #include <stdlib.h>
  49 #include <string.h>
  50 #include <assert.h>
  51 #include <ctype.h>
  52 #include <math.h>
  53
  54 #include "puzzles.h"
  55 #include "tree234.h"
  56
  57 #define PREFERRED_TILE_SIZE 32
  58 #define TILE_SIZE (ds->tilesize)
  59 #define LINEWIDTH TILE_SIZE / 16
  60 #define BORDER (TILE_SIZE / 2)
  61
  62 #define FLASH_TIME 0.4F
  63
  64 #define HL_COUNT(state) ((state)->w * ((state)->h + 1))
  65 #define VL_COUNT(state) (((state)->w + 1) * (state)->h)
  66 #define DOT_COUNT(state) (((state)->w + 1) * ((state)->h + 1))
  67 #define SQUARE_COUNT(state) ((state)->w * (state)->h)
  68
  69 #define ABOVE_SQUARE(state, i, j) ((state)->hl[(i) + (state)->w * (j)])
  70 #define BELOW_SQUARE(state, i, j) ABOVE_SQUARE(state, i, (j)+1)
  71
  72 #define LEFTOF_SQUARE(state, i, j)  ((state)->vl[(i) + ((state)->w + 1) * (j)])
  73 #define RIGHTOF_SQUARE(state, i, j) LEFTOF_SQUARE(state, (i)+1, j)
  74
  75 #define LEGAL_DOT(state, i, j) ((i) >= 0 && (j) >= 0 &&                 \
  76                                 (i) <= (state)->w && (j) <= (state)->h)
  77
  78 /*
  79  * These macros return rvalues only, but can cope with being passed
  80  * out-of-range coordinates.
  81  */
  82 #define ABOVE_DOT(state, i, j) ((!LEGAL_DOT(state, i, j) || j <= 0) ?  \
  83                                 LINE_NO : LV_ABOVE_DOT(state, i, j))
  84 #define BELOW_DOT(state, i, j) ((!LEGAL_DOT(state, i, j) || j >= (state)->h) ? \
  85                                 LINE_NO : LV_BELOW_DOT(state, i, j))
  86
  87 #define LEFTOF_DOT(state, i, j)  ((!LEGAL_DOT(state, i, j) || i <= 0) ? \
  88                                   LINE_NO : LV_LEFTOF_DOT(state, i, j))
  89 #define RIGHTOF_DOT(state, i, j) ((!LEGAL_DOT(state, i, j) || i >= (state)->w)?\
  90                                   LINE_NO : LV_RIGHTOF_DOT(state, i, j))
  91
  92 /*
  93  * These macros expect to be passed valid coordinates, and return
  94  * lvalues.
  95  */
  96 #define LV_BELOW_DOT(state, i, j) ((state)->vl[(i) + ((state)->w + 1) * (j)])
  97 #define LV_ABOVE_DOT(state, i, j) LV_BELOW_DOT(state, i, (j)-1)
  98
  99 #define LV_RIGHTOF_DOT(state, i, j) ((state)->hl[(i) + (state)->w * (j)])
 100 #define LV_LEFTOF_DOT(state, i, j)  LV_RIGHTOF_DOT(state, (i)-1, j)
 101
 102 #define CLUE_AT(state, i, j) ((i < 0 || i >= (state)->w || \
 103                                j < 0 || j >= (state)->h) ? \
 104                              ' ' : LV_CLUE_AT(state, i, j))
 105
 106 #define LV_CLUE_AT(state, i, j) ((state)->clues[(i) + (state)->w * (j)])
 107
 108 #define OPP(dir) (dir == LINE_UNKNOWN ? LINE_UNKNOWN : \
 109                   dir == LINE_YES ? LINE_NO : LINE_YES)
 110
 111 static char *game_text_format(game_state *state);
 112
 113 enum {
 114     COL_BACKGROUND,
 115     COL_FOREGROUND,
 116     COL_HIGHLIGHT,
 117     NCOLOURS
 118 };
 119
 120 enum line_state { LINE_UNKNOWN, LINE_YES, LINE_NO };
 121
 122 enum direction { UP, DOWN, LEFT, RIGHT };
 123
 124 struct game_params {
 125     int w, h, rec;
 126 };
 127
 128 struct game_state {
 129     int w, h;
 130
 131     /* Put ' ' in a square that doesn't get a clue */
 132     char *clues;
 133
 134     /* Arrays of line states, stored left-to-right, top-to-bottom */
 135     char *hl, *vl;
 136
 137     int solved;
 138     int cheated;
 139
 140     int recursion_depth;
 141 };
 142
 143 static game_state *dup_game(game_state *state)
 144 {
 145     game_state *ret = snew(game_state);
 146
 147     ret->h = state->h;
 148     ret->w = state->w;
 149     ret->solved = state->solved;
 150     ret->cheated = state->cheated;
 151
 152     ret->clues   = snewn(SQUARE_COUNT(state), char);
 153     memcpy(ret->clues, state->clues, SQUARE_COUNT(state));
 154
 155     ret->hl      = snewn(HL_COUNT(state), char);
 156     memcpy(ret->hl, state->hl, HL_COUNT(state));
 157
 158     ret->vl      = snewn(VL_COUNT(state), char);
 159     memcpy(ret->vl, state->vl, VL_COUNT(state));
 160
 161     ret->recursion_depth = state->recursion_depth;
 162
 163     return ret;
 164 }
 165
 166 static void free_game(game_state *state)
 167 {
 168     if (state) {
 169         sfree(state->clues);
 170         sfree(state->hl);
 171         sfree(state->vl);
 172         sfree(state);
 173     }
 174 }
 175
 176 enum solver_status {
 177     SOLVER_SOLVED,    /* This is the only solution the solver could find */
 178     SOLVER_MISTAKE,   /* This is definitely not a solution */
 179     SOLVER_AMBIGUOUS, /* This _might_ be an ambiguous solution */
 180     SOLVER_INCOMPLETE /* This may be a partial solution */
 181 };
 182
 183 typedef struct solver_state {
 184   game_state *state;
 185    /* XXX dot_atleastone[i,j, dline] is equivalent to */
 186    /*     dot_atmostone[i,j,OPP_DLINE(dline)] */
 187   char *dot_atleastone;
 188   char *dot_atmostone;
 189 /*   char *dline_identical; */
 190   int recursion_remaining;
 191   enum solver_status solver_status;
 192   int *dotdsf, *looplen;
 193 } solver_state;
 194
 195 static solver_state *new_solver_state(game_state *state) {
 196     solver_state *ret = snew(solver_state);
 197     int i;
 198
 199     ret->state = dup_game(state);
 200
 201     ret->dot_atmostone = snewn(DOT_COUNT(state), char);
 202     memset(ret->dot_atmostone, 0, DOT_COUNT(state));
 203     ret->dot_atleastone = snewn(DOT_COUNT(state), char);
 204     memset(ret->dot_atleastone, 0, DOT_COUNT(state));
 205
 206 #if 0
 207     dline_identical = snewn(DOT_COUNT(state), char);
 208     memset(dline_identical, 0, DOT_COUNT(state));
 209 #endif
 210
 211     ret->recursion_remaining = state->recursion_depth;
 212     ret->solver_status = SOLVER_INCOMPLETE; /* XXX This may be a lie */
 213
 214     ret->dotdsf = snewn(DOT_COUNT(state), int);
 215     ret->looplen = snewn(DOT_COUNT(state), int);
 216     for (i = 0; i < DOT_COUNT(state); i++) {
 217         ret->dotdsf[i] = i;
 218         ret->looplen[i] = 1;
 219     }
 220
 221     return ret;
 222 }
 223
 224 static void free_solver_state(solver_state *sstate) {
 225     if (sstate) {
 226         free_game(sstate->state);
 227         sfree(sstate->dot_atleastone);
 228         sfree(sstate->dot_atmostone);
 229         /*    sfree(sstate->dline_identical); */
 230         sfree(sstate->dotdsf);
 231         sfree(sstate->looplen);
 232         sfree(sstate);
 233     }
 234 }
 235
 236 static solver_state *dup_solver_state(solver_state *sstate) {
 237     game_state *state;
 238
 239     solver_state *ret = snew(solver_state);
 240
 241     ret->state = state = dup_game(sstate->state);
 242
 243     ret->dot_atmostone = snewn(DOT_COUNT(state), char);
 244     memcpy(ret->dot_atmostone, sstate->dot_atmostone, DOT_COUNT(state));
 245
 246     ret->dot_atleastone = snewn(DOT_COUNT(state), char);
 247     memcpy(ret->dot_atleastone, sstate->dot_atleastone, DOT_COUNT(state));
 248
 249 #if 0
 250     ret->dline_identical = snewn((state->w + 1) * (state->h + 1), char);
 251     memcpy(ret->dline_identical, state->dot_atmostone,
 252            (state->w + 1) * (state->h + 1));
 253 #endif
 254
 255     ret->recursion_remaining = sstate->recursion_remaining;
 256     ret->solver_status = sstate->solver_status;
 257
 258     ret->dotdsf = snewn(DOT_COUNT(state), int);
 259     ret->looplen = snewn(DOT_COUNT(state), int);
 260     memcpy(ret->dotdsf, sstate->dotdsf, DOT_COUNT(state) * sizeof(int));
 261     memcpy(ret->looplen, sstate->looplen, DOT_COUNT(state) * sizeof(int));
 262
 263     return ret;
 264 }
 265
 266 /*
 267  * Merge two dots due to the existence of an edge between them.
 268  * Updates the dsf tracking equivalence classes, and keeps track of
 269  * the length of path each dot is currently a part of.
 270  */
 271 static void merge_dots(solver_state *sstate, int x1, int y1, int x2, int y2)
 272 {
 273     int i, j, len;
 274
 275     i = y1 * (sstate->state->w + 1) + x1;
 276     j = y2 * (sstate->state->w + 1) + x2;
 277
 278     i = dsf_canonify(sstate->dotdsf, i);
 279     j = dsf_canonify(sstate->dotdsf, j);
 280
 281     if (i != j) {
 282         len = sstate->looplen[i] + sstate->looplen[j];
 283         dsf_merge(sstate->dotdsf, i, j);
 284         i = dsf_canonify(sstate->dotdsf, i);
 285         sstate->looplen[i] = len;
 286     }
 287 }
 288
 289 /* Count the number of lines of a particular type currently going into the
 290  * given dot.  Lines going off the edge of the board are assumed fixed no. */
 291 static int dot_order(const game_state* state, int i, int j, char line_type)
 292 {
 293     int n = 0;
 294
 295     if (i > 0) {
 296         if (LEFTOF_DOT(state, i, j) == line_type)
 297             ++n;
 298     } else {
 299         if (line_type == LINE_NO)
 300             ++n;
 301     }
 302     if (i < state->w) {
 303         if (RIGHTOF_DOT(state, i, j) == line_type)
 304             ++n;
 305     } else {
 306         if (line_type == LINE_NO)
 307             ++n;
 308     }
 309     if (j > 0) {
 310         if (ABOVE_DOT(state, i, j) == line_type)
 311             ++n;
 312     } else {
 313         if (line_type == LINE_NO)
 314             ++n;
 315     }
 316     if (j < state->h) {
 317         if (BELOW_DOT(state, i, j) == line_type)
 318             ++n;
 319     } else {
 320         if (line_type == LINE_NO)
 321             ++n;
 322     }
 323
 324     return n;
 325 }
 326 /* Count the number of lines of a particular type currently surrounding the
 327  * given square */
 328 static int square_order(const game_state* state, int i, int j, char line_type)
 329 {
 330     int n = 0;
 331
 332     if (ABOVE_SQUARE(state, i, j) == line_type)
 333         ++n;
 334     if (BELOW_SQUARE(state, i, j) == line_type)
 335         ++n;
 336     if (LEFTOF_SQUARE(state, i, j) == line_type)
 337         ++n;
 338     if (RIGHTOF_SQUARE(state, i, j) == line_type)
 339         ++n;
 340
 341     return n;
 342 }
 343
 344 /* Set all lines bordering a dot of type old_type to type new_type */
 345 static void dot_setall(game_state *state, int i, int j,
 346                        char old_type, char new_type)
 347 {
 348 /*    printf("dot_setall([%d,%d], %d, %d)\n", i, j, old_type, new_type); */
 349     if (i > 0        && LEFTOF_DOT(state, i, j) == old_type)
 350         LV_LEFTOF_DOT(state, i, j) = new_type;
 351     if (i < state->w && RIGHTOF_DOT(state, i, j) == old_type)
 352         LV_RIGHTOF_DOT(state, i, j) = new_type;
 353     if (j > 0        && ABOVE_DOT(state, i, j) == old_type)
 354         LV_ABOVE_DOT(state, i, j) = new_type;
 355     if (j < state->h && BELOW_DOT(state, i, j) == old_type)
 356         LV_BELOW_DOT(state, i, j) = new_type;
 357 }
 358 /* Set all lines bordering a square of type old_type to type new_type */
 359 static void square_setall(game_state *state, int i, int j,
 360                           char old_type, char new_type)
 361 {
 362     if (ABOVE_SQUARE(state, i, j) == old_type)
 363         ABOVE_SQUARE(state, i, j) = new_type;
 364     if (BELOW_SQUARE(state, i, j) == old_type)
 365         BELOW_SQUARE(state, i, j) = new_type;
 366     if (LEFTOF_SQUARE(state, i, j) == old_type)
 367         LEFTOF_SQUARE(state, i, j) = new_type;
 368     if (RIGHTOF_SQUARE(state, i, j) == old_type)
 369         RIGHTOF_SQUARE(state, i, j) = new_type;
 370 }
 371
 372 static game_params *default_params(void)
 373 {
 374     game_params *ret = snew(game_params);
 375
 376 #ifdef SLOW_SYSTEM
 377     ret->h = 4;
 378     ret->w = 4;
 379 #else
 380     ret->h = 10;
 381     ret->w = 10;
 382 #endif
 383     ret->rec = 0;
 384
 385     return ret;
 386 }
 387
 388 static game_params *dup_params(game_params *params)
 389 {
 390     game_params *ret = snew(game_params);
 391     *ret = *params;                       /* structure copy */
 392     return ret;
 393 }
 394
 395 static const struct {
 396     char *desc;
 397     game_params params;
 398 } loopy_presets[] = {
 399     { "4x4 Easy",   {  4,  4, 0 } },
 400     { "4x4 Hard",   {  4,  4, 2 } },
 401     { "7x7 Easy",   {  7,  7, 0 } },
 402     { "7x7 Hard",   {  7,  7, 2 } },
 403     { "10x10 Easy", { 10, 10, 0 } },
 404 #ifndef SLOW_SYSTEM
 405     { "10x10 Hard", { 10, 10, 2 } },
 406     { "15x15 Easy", { 15, 15, 0 } },
 407     { "30x20 Easy", { 30, 20, 0 } }
 408 #endif
 409 };
 410
 411 static int game_fetch_preset(int i, char **name, game_params **params)
 412 {
 413     game_params tmppar;
 414
 415     if (i < 0 || i >= lenof(loopy_presets))
 416         return FALSE;
 417
 418     tmppar = loopy_presets[i].params;
 419     *params = dup_params(&tmppar);
 420     *name = dupstr(loopy_presets[i].desc);
 421
 422     return TRUE;
 423 }
 424
 425 static void free_params(game_params *params)
 426 {
 427     sfree(params);
 428 }
 429
 430 static void decode_params(game_params *params, char const *string)
 431 {
 432     params->h = params->w = atoi(string);
 433     params->rec = 0;
 434     while (*string && isdigit((unsigned char)*string)) string++;
 435     if (*string == 'x') {
 436         string++;
 437         params->h = atoi(string);
 438         while (*string && isdigit((unsigned char)*string)) string++;
 439     }
 440     if (*string == 'r') {
 441         string++;
 442         params->rec = atoi(string);
 443         while (*string && isdigit((unsigned char)*string)) string++;
 444     }
 445 }
 446
 447 static char *encode_params(game_params *params, int full)
 448 {
 449     char str[80];
 450     sprintf(str, "%dx%d", params->w, params->h);
 451     if (full)
 452         sprintf(str + strlen(str), "r%d", params->rec);
 453     return dupstr(str);
 454 }
 455
 456 static config_item *game_configure(game_params *params)
 457 {
 458     config_item *ret;
 459     char buf[80];
 460
 461     ret = snewn(4, config_item);
 462
 463     ret[0].name = "Width";
 464     ret[0].type = C_STRING;
 465     sprintf(buf, "%d", params->w);
 466     ret[0].sval = dupstr(buf);
 467     ret[0].ival = 0;
 468
 469     ret[1].name = "Height";
 470     ret[1].type = C_STRING;
 471     sprintf(buf, "%d", params->h);
 472     ret[1].sval = dupstr(buf);
 473     ret[1].ival = 0;
 474
 475     ret[2].name = "Recursion depth";
 476     ret[2].type = C_STRING;
 477     sprintf(buf, "%d", params->rec);
 478     ret[2].sval = dupstr(buf);
 479     ret[2].ival = 0;
 480
 481     ret[3].name = NULL;
 482     ret[3].type = C_END;
 483     ret[3].sval = NULL;
 484     ret[3].ival = 0;
 485
 486     return ret;
 487 }
 488
 489 static game_params *custom_params(config_item *cfg)
 490 {
 491     game_params *ret = snew(game_params);
 492
 493     ret->w = atoi(cfg[0].sval);
 494     ret->h = atoi(cfg[1].sval);
 495     ret->rec = atoi(cfg[2].sval);
 496
 497     return ret;
 498 }
 499
 500 static char *validate_params(game_params *params, int full)
 501 {
 502     if (params->w < 4 || params->h < 4)
 503         return "Width and height must both be at least 4";
 504     if (params->rec < 0)
 505         return "Recursion depth can't be negative";
 506     return NULL;
 507 }
 508
 509 /* We're going to store a list of current candidate squares for lighting.
 510  * Each square gets a 'score', which tells us how adding that square right
 511  * now would affect the length of the solution loop.  We're trying to
 512  * maximise that quantity so will bias our random selection of squares to
 513  * light towards those with high scores */
 514 struct square {
 515     int score;
 516     unsigned long random;
 517     int x, y;
 518 };
 519
 520 static int get_square_cmpfn(void *v1, void *v2)
 521 {
 522     struct square *s1 = (struct square *)v1;
 523     struct square *s2 = (struct square *)v2;
 524     int r;
 525
 526     r = s1->x - s2->x;
 527     if (r)
 528         return r;
 529
 530     r = s1->y - s2->y;
 531     if (r)
 532         return r;
 533
 534     return 0;
 535 }
 536
 537 static int square_sort_cmpfn(void *v1, void *v2)
 538 {
 539     struct square *s1 = (struct square *)v1;
 540     struct square *s2 = (struct square *)v2;
 541     int r;
 542
 543     r = s2->score - s1->score;
 544     if (r) {
 545         return r;
 546     }
 547
 548     if (s1->random < s2->random)
 549         return -1;
 550     else if (s1->random > s2->random)
 551         return 1;
 552
 553     /*
 554      * It's _just_ possible that two squares might have been given
 555      * the same random value. In that situation, fall back to
 556      * comparing based on the coordinates. This introduces a tiny
 557      * directional bias, but not a significant one.
 558      */
 559     return get_square_cmpfn(v1, v2);
 560 }
 561
 562 static void print_tree(tree234 *tree)
 563 {
 564 #if 0
 565     int i = 0;
 566     struct square *s;
 567     printf("Print tree:\n");
 568     while (i < count234(tree)) {
 569         s = (struct square *)index234(tree, i);
 570         assert(s);
 571         printf("  [%d,%d], %d, %d\n", s->x, s->y, s->score, s->random);
 572         ++i;
 573     }
 574 #endif
 575 }
 576
 577 enum { SQUARE_LIT, SQUARE_UNLIT };
 578
 579 #define SQUARE_STATE(i, j)                 \
 580     (((i) < 0 || (i) >= params->w ||       \
 581       (j) < 0 || (j) >= params->h) ?       \
 582      SQUARE_UNLIT :  LV_SQUARE_STATE(i,j))
 583
 584 #define LV_SQUARE_STATE(i, j) board[(i) + params->w * (j)]
 585
 586 static void print_board(const game_params *params, const char *board)
 587 {
 588 #if 0
 589     int i,j;
 590
 591     printf(" ");
 592     for (i = 0; i < params->w; i++) {
 593         printf("%d", i%10);
 594     }
 595     printf("\n");
 596     for (j = 0; j < params->h; j++) {
 597         printf("%d", j%10);
 598         for (i = 0; i < params->w; i++) {
 599             printf("%c", SQUARE_STATE(i, j) ? ' ' : 'O');
 600         }
 601         printf("\n");
 602     }
 603 #endif
 604 }
 605
 606 static char *new_fullyclued_board(game_params *params, random_state *rs)
 607 {
 608     char *clues;
 609     char *board;
 610     int i, j, a, b, c;
 611     game_state s;
 612     game_state *state = &s;
 613     int board_area = SQUARE_COUNT(params);
 614     int t;
 615
 616     struct square *square, *tmpsquare, *sq;
 617     struct square square_pos;
 618
 619     /* These will contain exactly the same information, sorted into different
 620      * orders */
 621     tree234 *lightable_squares_sorted, *lightable_squares_gettable;
 622
 623 #define SQUARE_REACHABLE(i,j)                      \
 624      (t = (SQUARE_STATE(i-1, j) == SQUARE_LIT ||      \
 625            SQUARE_STATE(i+1, j) == SQUARE_LIT ||      \
 626            SQUARE_STATE(i, j-1) == SQUARE_LIT ||      \
 627            SQUARE_STATE(i, j+1) == SQUARE_LIT),       \
 628 /*      printf("SQUARE_REACHABLE(%d,%d) = %d\n", i, j, t), */ \
 629       t)
 630
 631
 632     /* One situation in which we may not light a square is if that'll leave one
 633      * square above/below and one left/right of us unlit, separated by a lit
 634      * square diagnonal from us */
 635 #define SQUARE_DIAGONAL_VIOLATION(i, j, h, v)           \
 636     (t = (SQUARE_STATE((i)+(h), (j))     == SQUARE_UNLIT && \
 637           SQUARE_STATE((i),     (j)+(v)) == SQUARE_UNLIT && \
 638           SQUARE_STATE((i)+(h), (j)+(v)) == SQUARE_LIT),    \
 639 /*     t ? printf("SQUARE_DIAGONAL_VIOLATION(%d, %d, %d, %d)\n",
 640                   i, j, h, v) : 0,*/ \
 641      t)
 642
 643     /* We also may not light a square if it will form a loop of lit squares
 644      * around some unlit squares, as then the game soln won't have a single
 645      * loop */
 646 #define SQUARE_LOOP_VIOLATION(i, j, lit1, lit2) \
 647     (SQUARE_STATE((i)+1, (j)) == lit1    &&     \
 648      SQUARE_STATE((i)-1, (j)) == lit1    &&     \
 649      SQUARE_STATE((i), (j)+1) == lit2    &&     \
 650      SQUARE_STATE((i), (j)-1) == lit2)
 651
 652 #define CAN_LIGHT_SQUARE(i, j)                                 \
 653     (SQUARE_REACHABLE(i, j)                                 && \
 654      !SQUARE_DIAGONAL_VIOLATION(i, j, -1, -1)               && \
 655      !SQUARE_DIAGONAL_VIOLATION(i, j, +1, -1)               && \
 656      !SQUARE_DIAGONAL_VIOLATION(i, j, -1, +1)               && \
 657      !SQUARE_DIAGONAL_VIOLATION(i, j, +1, +1)               && \
 658      !SQUARE_LOOP_VIOLATION(i, j, SQUARE_LIT, SQUARE_UNLIT) && \
 659      !SQUARE_LOOP_VIOLATION(i, j, SQUARE_UNLIT, SQUARE_LIT))
 660
 661 #define IS_LIGHTING_CANDIDATE(i, j)        \
 662     (SQUARE_STATE(i, j) == SQUARE_UNLIT && \
 663      CAN_LIGHT_SQUARE(i,j))
 664
 665     /* The 'score' of a square reflects its current desirability for selection
 666      * as the next square to light.  We want to encourage moving into uncharted
 667      * areas so we give scores according to how many of the square's neighbours
 668      * are currently unlit. */
 669
 670    /* UNLIT    SCORE
 671     *   3        2
 672     *   2        0
 673     *   1       -2
 674     */
 675 #define SQUARE_SCORE(i,j)                  \
 676     (2*((SQUARE_STATE(i-1, j) == SQUARE_UNLIT)  +   \
 677         (SQUARE_STATE(i+1, j) == SQUARE_UNLIT)  +   \
 678         (SQUARE_STATE(i, j-1) == SQUARE_UNLIT)  +   \
 679         (SQUARE_STATE(i, j+1) == SQUARE_UNLIT)) - 4)
 680
 681     /* When a square gets lit, this defines how far away from that square we
 682      * need to go recomputing scores */
 683 #define SCORE_DISTANCE 1
 684
 685     board = snewn(board_area, char);
 686     clues = snewn(board_area, char);
 687
 688     state->h = params->h;
 689     state->w = params->w;
 690     state->clues = clues;
 691
 692     /* Make a board */
 693     memset(board, SQUARE_UNLIT, board_area);
 694
 695     /* Seed the board with a single lit square near the middle */
 696     i = params->w / 2;
 697     j = params->h / 2;
 698     if (params->w & 1 && random_bits(rs, 1))
 699         ++i;
 700     if (params->h & 1 && random_bits(rs, 1))
 701         ++j;
 702
 703     LV_SQUARE_STATE(i, j) = SQUARE_LIT;
 704
 705     /* We need a way of favouring squares that will increase our loopiness.
 706      * We do this by maintaining a list of all candidate squares sorted by
 707      * their score and choose randomly from that with appropriate skew.
 708      * In order to avoid consistently biasing towards particular squares, we
 709      * need the sort order _within_ each group of scores to be completely
 710      * random.  But it would be abusing the hospitality of the tree234 data
 711      * structure if our comparison function were nondeterministic :-).  So with
 712      * each square we associate a random number that does not change during a
 713      * particular run of the generator, and use that as a secondary sort key.
 714      * Yes, this means we will be biased towards particular random squares in
 715      * any one run but that doesn't actually matter. */
 716
 717     lightable_squares_sorted   = newtree234(square_sort_cmpfn);
 718     lightable_squares_gettable = newtree234(get_square_cmpfn);
 719 #define ADD_SQUARE(s)                                          \
 720     do {                                                       \
 721 /*      printf("ADD SQUARE: [%d,%d], %d, %d\n",
 722                s->x, s->y, s->score, s->random);*/ \
 723         sq = add234(lightable_squares_sorted, s);              \
 724         assert(sq == s);                                       \
 725         sq = add234(lightable_squares_gettable, s);            \
 726         assert(sq == s);                                       \
 727     } while (0)
 728
 729 #define REMOVE_SQUARE(s)                                       \
 730     do {                                                       \
 731 /*      printf("DELETE SQUARE: [%d,%d], %d, %d\n",
 732                s->x, s->y, s->score, s->random);*/ \
 733         sq = del234(lightable_squares_sorted, s);              \
 734         assert(sq);                                            \
 735         sq = del234(lightable_squares_gettable, s);            \
 736         assert(sq);                                            \
 737     } while (0)
 738
 739 #define HANDLE_DIR(a, b)                                       \
 740     square = snew(struct square);                              \
 741     square->x = (i)+(a);                                       \
 742     square->y = (j)+(b);                                       \
 743     square->score = 2;                                         \
 744     square->random = random_bits(rs, 31);                      \
 745     ADD_SQUARE(square);
 746     HANDLE_DIR(-1, 0);
 747     HANDLE_DIR( 1, 0);
 748     HANDLE_DIR( 0,-1);
 749     HANDLE_DIR( 0, 1);
 750 #undef HANDLE_DIR
 751
 752     /* Light squares one at a time until the board is interesting enough */
 753     while (TRUE)
 754     {
 755         /* We have count234(lightable_squares) possibilities, and in
 756          * lightable_squares_sorted they are sorted with the most desirable
 757          * first.  */
 758         c = count234(lightable_squares_sorted);
 759         if (c == 0)
 760             break;
 761         assert(c == count234(lightable_squares_gettable));
 762
 763         /* Check that the best square available is any good */
 764         square = (struct square *)index234(lightable_squares_sorted, 0);
 765         assert(square);
 766
 767         /*
 768          * We never want to _decrease_ the loop's perimeter. Making
 769          * moves that leave the perimeter the same is occasionally
 770          * useful: if it were _never_ done then the user would be
 771          * able to deduce illicitly that any degree-zero vertex was
 772          * on the outside of the loop. So we do it sometimes but
 773          * not always.
 774          */
 775         if (square->score < 0 || (square->score == 0 &&
 776                                   random_upto(rs, 2) == 0))
 777             break;
 778
 779         print_tree(lightable_squares_sorted);
 780         assert(square->score == SQUARE_SCORE(square->x, square->y));
 781         assert(SQUARE_STATE(square->x, square->y) == SQUARE_UNLIT);
 782         assert(square->x >= 0 && square->x < params->w);
 783         assert(square->y >= 0 && square->y < params->h);
 784 /*        printf("LIGHT SQUARE: [%d,%d], score = %d\n", square->x, square->y, square->score); */
 785
 786         /* Update data structures */
 787         LV_SQUARE_STATE(square->x, square->y) = SQUARE_LIT;
 788         REMOVE_SQUARE(square);
 789
 790         print_board(params, board);
 791
 792         /* We might have changed the score of any squares up to 2 units away in
 793          * any direction */
 794         for (b = -SCORE_DISTANCE; b <= SCORE_DISTANCE; b++) {
 795             for (a = -SCORE_DISTANCE; a <= SCORE_DISTANCE; a++) {
 796                 if (!a && !b)
 797                     continue;
 798                 square_pos.x = square->x + a;
 799                 square_pos.y = square->y + b;
 800 /*                printf("Refreshing score for [%d,%d]:\n", square_pos.x, square_pos.y); */
 801                 if (square_pos.x < 0 || square_pos.x >= params->w ||
 802                     square_pos.y < 0 || square_pos.y >= params->h) {
 803 /*                    printf("  Out of bounds\n"); */
 804                    continue;
 805                 }
 806                 tmpsquare = find234(lightable_squares_gettable, &square_pos,
 807                                     NULL);
 808                 if (tmpsquare) {
 809 /*                    printf(" Removing\n"); */
 810                     assert(tmpsquare->x == square_pos.x);
 811                     assert(tmpsquare->y == square_pos.y);
 812                     assert(SQUARE_STATE(tmpsquare->x, tmpsquare->y) ==
 813                            SQUARE_UNLIT);
 814                     REMOVE_SQUARE(tmpsquare);
 815                 } else {
 816 /*                    printf(" Creating\n"); */
 817                     tmpsquare = snew(struct square);
 818                     tmpsquare->x = square_pos.x;
 819                     tmpsquare->y = square_pos.y;
 820                     tmpsquare->random = random_bits(rs, 31);
 821                 }
 822                 tmpsquare->score = SQUARE_SCORE(tmpsquare->x, tmpsquare->y);
 823
 824                 if (IS_LIGHTING_CANDIDATE(tmpsquare->x, tmpsquare->y)) {
 825 /*                    printf(" Adding\n"); */
 826                     ADD_SQUARE(tmpsquare);
 827                 } else {
 828 /*                    printf(" Destroying\n"); */
 829                     sfree(tmpsquare);
 830                 }
 831             }
 832         }
 833         sfree(square);
 834 /*        printf("\n\n"); */
 835     }
 836
 837     while ((square = delpos234(lightable_squares_gettable, 0)) != NULL)
 838         sfree(square);
 839     freetree234(lightable_squares_gettable);
 840     freetree234(lightable_squares_sorted);
 841
 842     /* Copy out all the clues */
 843     for (j = 0; j < params->h; ++j) {
 844         for (i = 0; i < params->w; ++i) {
 845             c = SQUARE_STATE(i, j);
 846             LV_CLUE_AT(state, i, j) = '0';
 847             if (SQUARE_STATE(i-1, j) != c) ++LV_CLUE_AT(state, i, j);
 848             if (SQUARE_STATE(i+1, j) != c) ++LV_CLUE_AT(state, i, j);
 849             if (SQUARE_STATE(i, j-1) != c) ++LV_CLUE_AT(state, i, j);
 850             if (SQUARE_STATE(i, j+1) != c) ++LV_CLUE_AT(state, i, j);
 851         }
 852     }
 853
 854     sfree(board);
 855     return clues;
 856 }
 857
 858 static solver_state *solve_game_rec(const solver_state *sstate);
 859
 860 static int game_has_unique_soln(const game_state *state)
 861 {
 862     int ret;
 863     solver_state *sstate_new;
 864     solver_state *sstate = new_solver_state((game_state *)state);
 865
 866     sstate_new = solve_game_rec(sstate);
 867
 868     ret = (sstate_new->solver_status == SOLVER_SOLVED);
 869
 870     free_solver_state(sstate_new);
 871     free_solver_state(sstate);
 872
 873     return ret;
 874 }
 875
 876 /* Remove clues one at a time at random. */
 877 static game_state *remove_clues(game_state *state, random_state *rs)
 878 {
 879     int *square_list, squares;
 880     game_state *ret = dup_game(state), *saved_ret;
 881     int n;
 882
 883     /* We need to remove some clues.  We'll do this by forming a list of all
 884      * available equivalence classes, shuffling it, then going along one at a
 885      * time clearing every member of each equivalence class, where removing a
 886      * class doesn't render the board unsolvable. */
 887     squares = state->w * state->h;
 888     square_list = snewn(squares, int);
 889     for (n = 0; n < squares; ++n) {
 890         square_list[n] = n;
 891     }
 892
 893     shuffle(square_list, squares, sizeof(int), rs);
 894
 895     for (n = 0; n < squares; ++n) {
 896         saved_ret = dup_game(ret);
 897         LV_CLUE_AT(ret, square_list[n] % state->w,
 898                    square_list[n] / state->w) = ' ';
 899         if (game_has_unique_soln(ret)) {
 900             free_game(saved_ret);
 901         } else {
 902             free_game(ret);
 903             ret = saved_ret;
 904         }
 905     }
 906     sfree(square_list);
 907
 908     return ret;
 909 }
 910
 911 static char *validate_desc(game_params *params, char *desc);
 912
 913 static char *new_game_desc(game_params *params, random_state *rs,
 914                            char **aux, int interactive)
 915 {
 916     /* solution and description both use run-length encoding in obvious ways */
 917     char *retval;
 918     char *description = snewn(SQUARE_COUNT(params) + 1, char);
 919     char *dp = description;
 920     int i, j;
 921     int empty_count;
 922     game_state *state = snew(game_state), *state_new;
 923
 924     state->h = params->h;
 925     state->w = params->w;
 926
 927     state->hl = snewn(HL_COUNT(params), char);
 928     state->vl = snewn(VL_COUNT(params), char);
 929     memset(state->hl, LINE_UNKNOWN, HL_COUNT(params));
 930     memset(state->vl, LINE_UNKNOWN, VL_COUNT(params));
 931
 932     state->solved = state->cheated = FALSE;
 933     state->recursion_depth = params->rec;
 934
 935     /* Get a new random solvable board with all its clues filled in.  Yes, this
 936      * can loop for ever if the params are suitably unfavourable, but
 937      * preventing games smaller than 4x4 seems to stop this happening */
 938     do {
 939         state->clues = new_fullyclued_board(params, rs);
 940     } while (!game_has_unique_soln(state));
 941
 942     state_new = remove_clues(state, rs);
 943     free_game(state);
 944     state = state_new;
 945
 946     empty_count = 0;
 947     for (j = 0; j < params->h; ++j) {
 948         for (i = 0; i < params->w; ++i) {
 949             if (CLUE_AT(state, i, j) == ' ') {
 950                 if (empty_count > 25) {
 951                     dp += sprintf(dp, "%c", (int)(empty_count + 'a' - 1));
 952                     empty_count = 0;
 953                 }
 954                 empty_count++;
 955             } else {
 956                 if (empty_count) {
 957                     dp += sprintf(dp, "%c", (int)(empty_count + 'a' - 1));
 958                     empty_count = 0;
 959                 }
 960                 dp += sprintf(dp, "%c", (int)(CLUE_AT(state, i, j)));
 961             }
 962         }
 963     }
 964     if (empty_count)
 965         dp += sprintf(dp, "%c", (int)(empty_count + 'a' - 1));
 966
 967     free_game(state);
 968     retval = dupstr(description);
 969     sfree(description);
 970
 971     assert(!validate_desc(params, retval));
 972
 973     return retval;
 974 }
 975
 976 /* We require that the params pass the test in validate_params and that the
 977  * description fills the entire game area */
 978 static char *validate_desc(game_params *params, char *desc)
 979 {
 980     int count = 0;
 981
 982     for (; *desc; ++desc) {
 983         if (*desc >= '0' && *desc <= '9') {
 984             count++;
 985             continue;
 986         }
 987         if (*desc >= 'a') {
 988             count += *desc - 'a' + 1;
 989             continue;
 990         }
 991         return "Unknown character in description";
 992     }
 993
 994     if (count < SQUARE_COUNT(params))
 995         return "Description too short for board size";
 996     if (count > SQUARE_COUNT(params))
 997         return "Description too long for board size";
 998
 999     return NULL;
1000 }
1001
1002 static game_state *new_game(midend *me, game_params *params, char *desc)
1003 {
1004     int i,j;
1005     game_state *state = snew(game_state);
1006     int empties_to_make = 0;
1007     int n;
1008     const char *dp = desc;
1009
1010     state->recursion_depth = params->rec;
1011
1012     state->h = params->h;
1013     state->w = params->w;
1014
1015     state->clues = snewn(SQUARE_COUNT(params), char);
1016     state->hl    = snewn(HL_COUNT(params), char);
1017     state->vl    = snewn(VL_COUNT(params), char);
1018
1019     state->solved = state->cheated = FALSE;
1020
1021     for (j = 0 ; j < params->h; ++j) {
1022         for (i = 0 ; i < params->w; ++i) {
1023             if (empties_to_make) {
1024                 empties_to_make--;
1025                 LV_CLUE_AT(state, i, j) = ' ';
1026                 continue;
1027             }
1028
1029             assert(*dp);
1030             n = *dp - '0';
1031             if (n >=0 && n < 10) {
1032                 LV_CLUE_AT(state, i, j) = *dp;
1033             } else {
1034                 n = *dp - 'a' + 1;
1035                 assert(n > 0);
1036                 LV_CLUE_AT(state, i, j) = ' ';
1037                 empties_to_make = n - 1;
1038             }
1039             ++dp;
1040         }
1041     }
1042
1043     memset(state->hl, LINE_UNKNOWN, HL_COUNT(params));
1044     memset(state->vl, LINE_UNKNOWN, VL_COUNT(params));
1045
1046     return state;
1047 }
1048
1049 enum { LOOP_NONE=0, LOOP_SOLN, LOOP_NOT_SOLN };
1050
1051 /* Starting at dot [i,j] moves around 'state' removing lines until it's clear
1052  * whether or not the starting dot was on a loop.  Returns boolean specifying
1053  * whether a loop was found.  loop_status calls this and assumes that if state
1054  * has any lines set, this function will always remove at least one.  */
1055 static int destructively_find_loop(game_state *state)
1056 {
1057     int a, b, i, j, new_i, new_j, n;
1058     char *lp;
1059
1060     lp = (char *)memchr(state->hl, LINE_YES, HL_COUNT(state));
1061     if (!lp) {
1062         /* We know we're going to return false but we have to fulfil our
1063          * contract */
1064         lp = (char *)memchr(state->vl, LINE_YES, VL_COUNT(state));
1065         if (lp)
1066             *lp = LINE_NO;
1067
1068         return FALSE;
1069     }
1070
1071     n = lp - state->hl;
1072
1073     i = n % state->w;
1074     j = n / state->w;
1075
1076     assert(i + j * state->w == n); /* because I'm feeling stupid */
1077     /* Save start position */
1078     a = i;
1079     b = j;
1080
1081     /* Delete one line from the potential loop */
1082     if (LEFTOF_DOT(state, i, j) == LINE_YES) {
1083         LV_LEFTOF_DOT(state, i, j) = LINE_NO;
1084         i--;
1085     } else if (ABOVE_DOT(state, i, j) == LINE_YES) {
1086         LV_ABOVE_DOT(state, i, j) = LINE_NO;
1087         j--;
1088     } else if (RIGHTOF_DOT(state, i, j) == LINE_YES) {
1089         LV_RIGHTOF_DOT(state, i, j) = LINE_NO;
1090         i++;
1091     } else if (BELOW_DOT(state, i, j) == LINE_YES) {
1092         LV_BELOW_DOT(state, i, j) = LINE_NO;
1093         j++;
1094     } else {
1095         return FALSE;
1096     }
1097
1098     do {
1099         /* From the current position of [i,j] there needs to be exactly one
1100          * line */
1101         new_i = new_j = -1;
1102
1103 #define HANDLE_DIR(dir_dot, x, y)                    \
1104         if (dir_dot(state, i, j) == LINE_YES) {      \
1105             if (new_i != -1 || new_j != -1)          \
1106                 return FALSE;                        \
1107             new_i = (i)+(x);                         \
1108             new_j = (j)+(y);                         \
1109             LV_##dir_dot(state, i, j) = LINE_NO;     \
1110         }
1111         HANDLE_DIR(ABOVE_DOT,    0, -1);
1112         HANDLE_DIR(BELOW_DOT,    0, +1);
1113         HANDLE_DIR(LEFTOF_DOT,  -1,  0);
1114         HANDLE_DIR(RIGHTOF_DOT, +1,  0);
1115 #undef HANDLE_DIR
1116         if (new_i == -1 || new_j == -1) {
1117             return FALSE;
1118         }
1119
1120         i = new_i;
1121         j = new_j;
1122     } while (i != a || j != b);
1123
1124     return TRUE;
1125 }
1126
1127 static int loop_status(game_state *state)
1128 {
1129     int i, j, n;
1130     game_state *tmpstate;
1131     int loop_found = FALSE, non_loop_found = FALSE, any_lines_found = FALSE;
1132
1133 #define BAD_LOOP_FOUND \
1134     do { free_game(tmpstate); return LOOP_NOT_SOLN; } while(0)
1135
1136     /* Repeatedly look for loops until we either run out of lines to consider
1137      * or discover for sure that the board fails on the grounds of having no
1138      * loop */
1139     tmpstate = dup_game(state);
1140
1141     while (TRUE) {
1142         if (!memchr(tmpstate->hl, LINE_YES, HL_COUNT(tmpstate)) &&
1143             !memchr(tmpstate->vl, LINE_YES, VL_COUNT(tmpstate))) {
1144             break;
1145         }
1146         any_lines_found = TRUE;
1147
1148         if (loop_found)
1149             BAD_LOOP_FOUND;
1150         if (destructively_find_loop(tmpstate)) {
1151             loop_found = TRUE;
1152             if (non_loop_found)
1153                 BAD_LOOP_FOUND;
1154         } else {
1155             non_loop_found = TRUE;
1156         }
1157     }
1158
1159     free_game(tmpstate);
1160
1161     if (!any_lines_found)
1162         return LOOP_NONE;
1163
1164     if (non_loop_found) {
1165         assert(!loop_found); /* should have dealt with this already */
1166         return LOOP_NONE;
1167     }
1168
1169     /* Check that every clue is satisfied */
1170     for (j = 0; j < state->h; ++j) {
1171         for (i = 0; i < state->w; ++i) {
1172             n = CLUE_AT(state, i, j);
1173             if (n != ' ') {
1174                 if (square_order(state, i, j, LINE_YES) != n - '0') {
1175                     return LOOP_NOT_SOLN;
1176                 }
1177             }
1178         }
1179     }
1180
1181     return LOOP_SOLN;
1182 }
1183
1184 /* Sums the lengths of the numbers in range [0,n) */
1185 /* See equivalent function in solo.c for justification of this. */
1186 static int len_0_to_n(int n)
1187 {
1188     int len = 1; /* Counting 0 as a bit of a special case */
1189     int i;
1190
1191     for (i = 1; i < n; i *= 10) {
1192         len += max(n - i, 0);
1193     }
1194
1195     return len;
1196 }
1197
1198 static char *encode_solve_move(const game_state *state)
1199 {
1200     int len, i, j;
1201     char *ret, *p;
1202     /* This is going to return a string representing the moves needed to set
1203      * every line in a grid to be the same as the ones in 'state'.  The exact
1204      * length of this string is predictable. */
1205
1206     len = 1;  /* Count the 'S' prefix */
1207     /* Numbers in horizontal lines */
1208     /* Horizontal lines, x position */
1209     len += len_0_to_n(state->w) * (state->h + 1);
1210     /* Horizontal lines, y position */
1211     len += len_0_to_n(state->h + 1) * (state->w);
1212     /* Vertical lines, y position */
1213     len += len_0_to_n(state->h) * (state->w + 1);
1214     /* Vertical lines, x position */
1215     len += len_0_to_n(state->w + 1) * (state->h);
1216     /* For each line we also have two letters and a comma */
1217     len += 3 * (HL_COUNT(state) + VL_COUNT(state));
1218
1219     ret = snewn(len + 1, char);
1220     p = ret;
1221
1222     p += sprintf(p, "S");
1223
1224     for (j = 0; j < state->h + 1; ++j) {
1225         for (i = 0; i < state->w; ++i) {
1226             switch (RIGHTOF_DOT(state, i, j)) {
1227                 case LINE_YES:
1228                     p += sprintf(p, "%d,%dhy", i, j);
1229                     break;
1230                 case LINE_NO:
1231                     p += sprintf(p, "%d,%dhn", i, j);
1232                     break;
1233 /*                default: */
1234                     /* I'm going to forgive this because I think the results
1235                      * are cute. */
1236 /*                    assert(!"Solver produced incomplete solution!"); */
1237             }
1238         }
1239     }
1240
1241     for (j = 0; j < state->h; ++j) {
1242         for (i = 0; i < state->w + 1; ++i) {
1243             switch (BELOW_DOT(state, i, j)) {
1244                 case LINE_YES:
1245                     p += sprintf(p, "%d,%dvy", i, j);
1246                     break;
1247                 case LINE_NO:
1248                     p += sprintf(p, "%d,%dvn", i, j);
1249                     break;
1250 /*                default: */
1251                     /* I'm going to forgive this because I think the results
1252                      * are cute. */
1253 /*                    assert(!"Solver produced incomplete solution!"); */
1254             }
1255         }
1256     }
1257
1258     /* No point in doing sums like that if they're going to be wrong */
1259     assert(strlen(ret) <= (size_t)len);
1260     return ret;
1261 }
1262
1263 /* BEGIN SOLVER IMPLEMENTATION */
1264
1265    /* For each pair of lines through each dot we store a bit for whether
1266     * exactly one of those lines is ON, and in separate arrays we store whether
1267     * at least one is on and whether at most 1 is on.  (If we know both or
1268     * neither is on that's already stored more directly.)  That's six bits per
1269     * dot.  Bit number n represents the lines shown in dot_type_dirs[n]. */
1270
1271 enum dline {
1272     DLINE_VERT  = 0,
1273     DLINE_HORIZ = 1,
1274     DLINE_UL    = 2,
1275     DLINE_DR    = 3,
1276     DLINE_UR    = 4,
1277     DLINE_DL    = 5
1278 };
1279
1280 #define OPP_DLINE(dline) (dline ^ 1)
1281
1282
1283 #define SQUARE_DLINES                                                          \
1284                    HANDLE_DLINE(DLINE_UL, RIGHTOF_SQUARE, BELOW_SQUARE, 1, 1); \
1285                    HANDLE_DLINE(DLINE_UR, LEFTOF_SQUARE,  BELOW_SQUARE, 0, 1); \
1286                    HANDLE_DLINE(DLINE_DL, RIGHTOF_SQUARE, ABOVE_SQUARE, 1, 0); \
1287                    HANDLE_DLINE(DLINE_DR, LEFTOF_SQUARE,  ABOVE_SQUARE, 0, 0);
1288
1289 #define DOT_DLINES                                                       \
1290                    HANDLE_DLINE(DLINE_VERT,  ABOVE_DOT,  BELOW_DOT);     \
1291                    HANDLE_DLINE(DLINE_HORIZ, LEFTOF_DOT, RIGHTOF_DOT);   \
1292                    HANDLE_DLINE(DLINE_UL,    ABOVE_DOT,  LEFTOF_DOT);    \
1293                    HANDLE_DLINE(DLINE_UR,    ABOVE_DOT,  RIGHTOF_DOT);   \
1294                    HANDLE_DLINE(DLINE_DL,    BELOW_DOT,  LEFTOF_DOT);    \
1295                    HANDLE_DLINE(DLINE_DR,    BELOW_DOT,  RIGHTOF_DOT);
1296
1297 static void array_setall(char *array, char from, char to, int len)
1298 {
1299     char *p = array, *p_old = p;
1300     int len_remaining = len;
1301
1302     while ((p = memchr(p, from, len_remaining))) {
1303         *p = to;
1304         len_remaining -= p - p_old;
1305         p_old = p;
1306     }
1307 }
1308
1309
1310 static int game_states_equal(const game_state *state1,
1311                              const game_state *state2)
1312 {
1313     /* This deliberately doesn't check _all_ fields, just the ones that make a
1314      * game state 'interesting' from the POV of the solver */
1315     /* XXX review this */
1316     if (state1 == state2)
1317         return 1;
1318
1319     if (!state1 || !state2)
1320         return 0;
1321
1322     if (state1->w != state2->w || state1->h != state2->h)
1323         return 0;
1324
1325     if (memcmp(state1->hl, state2->hl, HL_COUNT(state1)))
1326         return 0;
1327
1328     if (memcmp(state1->vl, state2->vl, VL_COUNT(state1)))
1329         return 0;
1330
1331     return 1;
1332 }
1333
1334 static int solver_states_equal(const solver_state *sstate1,
1335                                const solver_state *sstate2)
1336 {
1337     if (!sstate1) {
1338         if (!sstate2)
1339             return TRUE;
1340         else
1341             return FALSE;
1342     }
1343
1344     if (!game_states_equal(sstate1->state, sstate2->state)) {
1345         return 0;
1346     }
1347
1348     /* XXX fields missing, needs review */
1349     /* XXX we're deliberately not looking at solver_state as it's only a cache */
1350
1351     if (memcmp(sstate1->dot_atleastone, sstate2->dot_atleastone,
1352                DOT_COUNT(sstate1->state))) {
1353         return 0;
1354     }
1355
1356     if (memcmp(sstate1->dot_atmostone, sstate2->dot_atmostone,
1357                DOT_COUNT(sstate1->state))) {
1358         return 0;
1359     }
1360
1361     /* handle dline_identical here */
1362
1363     return 1;
1364 }
1365
1366 static void dot_setall_dlines(solver_state *sstate, enum dline dl, int i, int j,
1367                               enum line_state line_old, enum line_state line_new)
1368 {
1369     game_state *state = sstate->state;
1370
1371     /* First line in dline */
1372     switch (dl) {
1373         case DLINE_UL:
1374         case DLINE_UR:
1375         case DLINE_VERT:
1376             if (j > 0 && ABOVE_DOT(state, i, j) == line_old)
1377                 LV_ABOVE_DOT(state, i, j) = line_new;
1378             break;
1379         case DLINE_DL:
1380         case DLINE_DR:
1381             if (j <= (state)->h && BELOW_DOT(state, i, j) == line_old)
1382                 LV_BELOW_DOT(state, i, j) = line_new;
1383             break;
1384         case DLINE_HORIZ:
1385             if (i > 0 && LEFTOF_DOT(state, i, j) == line_old)
1386                 LV_LEFTOF_DOT(state, i, j) = line_new;
1387             break;
1388     }
1389
1390     /* Second line in dline */
1391     switch (dl) {
1392         case DLINE_UL:
1393         case DLINE_DL:
1394             if (i > 0 && LEFTOF_DOT(state, i, j) == line_old)
1395                 LV_LEFTOF_DOT(state, i, j) = line_new;
1396             break;
1397         case DLINE_UR:
1398         case DLINE_DR:
1399         case DLINE_HORIZ:
1400             if (i <= (state)->w && RIGHTOF_DOT(state, i, j) == line_old)
1401                 LV_RIGHTOF_DOT(state, i, j) = line_new;
1402             break;
1403         case DLINE_VERT:
1404             if (j <= (state)->h && BELOW_DOT(state, i, j) == line_old)
1405                 LV_BELOW_DOT(state, i, j) = line_new;
1406             break;
1407     }
1408 }
1409
1410 static void update_solver_status(solver_state *sstate)
1411 {
1412     if (sstate->solver_status == SOLVER_INCOMPLETE) {
1413         switch (loop_status(sstate->state)) {
1414             case LOOP_NONE:
1415                 sstate->solver_status = SOLVER_INCOMPLETE;
1416                 break;
1417             case LOOP_SOLN:
1418                 if (sstate->solver_status != SOLVER_AMBIGUOUS)
1419                     sstate->solver_status = SOLVER_SOLVED;
1420                 break;
1421             case LOOP_NOT_SOLN:
1422                 sstate->solver_status = SOLVER_MISTAKE;
1423                 break;
1424         }
1425     }
1426 }
1427
1428
1429 /* This will return a dynamically allocated solver_state containing the (more)
1430  * solved grid */
1431 static solver_state *solve_game_rec(const solver_state *sstate_start)
1432 {
1433    int i, j;
1434    int current_yes, current_no, desired;
1435    solver_state *sstate, *sstate_saved, *sstate_tmp;
1436    int t;
1437 /*   char *text; */
1438    solver_state *sstate_rec_solved;
1439    int recursive_soln_count;
1440
1441 #if 0
1442    printf("solve_game_rec: recursion_remaining = %d\n",
1443           sstate_start->recursion_remaining);
1444 #endif
1445
1446    sstate = dup_solver_state((solver_state *)sstate_start);
1447
1448 #if 0
1449    text = game_text_format(sstate->state);
1450    printf("%s\n", text);
1451    sfree(text);
1452 #endif
1453
1454 #define RETURN_IF_SOLVED                                 \
1455    do {                                                  \
1456        update_solver_status(sstate);                     \
1457        if (sstate->solver_status != SOLVER_INCOMPLETE) { \
1458            free_solver_state(sstate_saved);              \
1459            return sstate;                                \
1460        }                                                 \
1461    } while (0)
1462
1463    sstate_saved = NULL;
1464    RETURN_IF_SOLVED;
1465
1466 nonrecursive_solver:
1467
1468    while (1) {
1469        sstate_saved = dup_solver_state(sstate);
1470
1471        /* First we do the 'easy' work, that might cause concrete results */
1472
1473        /* Per-square deductions */
1474        for (j = 0; j < sstate->state->h; ++j) {
1475            for (i = 0; i < sstate->state->w; ++i) {
1476                /* Begin rules that look at the clue (if there is one) */
1477                desired = CLUE_AT(sstate->state, i, j);
1478                if (desired == ' ')
1479                    continue;
1480                desired = desired - '0';
1481                current_yes = square_order(sstate->state, i, j, LINE_YES);
1482                current_no  = square_order(sstate->state, i, j, LINE_NO);
1483
1484                if (desired <= current_yes) {
1485                    square_setall(sstate->state, i, j, LINE_UNKNOWN, LINE_NO);
1486                    continue;
1487                }
1488
1489                if (4 - desired <= current_no) {
1490                    square_setall(sstate->state, i, j, LINE_UNKNOWN, LINE_YES);
1491                }
1492            }
1493        }
1494
1495        RETURN_IF_SOLVED;
1496
1497        /* Per-dot deductions */
1498        for (j = 0; j < sstate->state->h + 1; ++j) {
1499            for (i = 0; i < sstate->state->w + 1; ++i) {
1500                switch (dot_order(sstate->state, i, j, LINE_YES)) {
1501                case 0:
1502                    if (dot_order(sstate->state, i, j, LINE_NO) == 3) {
1503                        dot_setall(sstate->state, i, j, LINE_UNKNOWN, LINE_NO);
1504                    }
1505                    break;
1506                case 1:
1507                    switch (dot_order(sstate->state, i, j, LINE_NO)) {
1508 #define H1(dline, dir1_dot, dir2_dot, dot_howmany)                             \
1509                        if (dir1_dot(sstate->state, i, j) == LINE_UNKNOWN) {    \
1510                            if (dir2_dot(sstate->state, i, j) == LINE_UNKNOWN){ \
1511                                sstate->dot_howmany                             \
1512                                  [i + (sstate->state->w + 1) * j] |= 1<<dline; \
1513                            }                                                   \
1514                        }
1515                        case 1:
1516 #define HANDLE_DLINE(dline, dir1_dot, dir2_dot)                               \
1517                            H1(dline, dir1_dot, dir2_dot, dot_atleastone)
1518                            /* 1 yes, 1 no, so exactly one of unknowns is yes */
1519                            DOT_DLINES;
1520 #undef HANDLE_DLINE
1521                            /* fall through */
1522                        case 0:
1523 #define HANDLE_DLINE(dline, dir1_dot, dir2_dot)                               \
1524                            H1(dline, dir1_dot, dir2_dot, dot_atmostone)
1525                            /* 1 yes, fewer than 2 no, so at most one of
1526                             * unknowns is yes */
1527                            DOT_DLINES;
1528 #undef HANDLE_DLINE
1529 #undef H1
1530                            break;
1531                        case 2: /* 1 yes, 2 no */
1532                            dot_setall(sstate->state, i, j,
1533                                       LINE_UNKNOWN, LINE_YES);
1534                            break;
1535                    }
1536                    break;
1537                case 2:
1538                case 3:
1539                    dot_setall(sstate->state, i, j, LINE_UNKNOWN, LINE_NO);
1540                }
1541 #define HANDLE_DLINE(dline, dir1_dot, dir2_dot)                               \
1542                if (sstate->dot_atleastone                                     \
1543                      [i + (sstate->state->w + 1) * j] & 1<<dline) {           \
1544                    sstate->dot_atmostone                                      \
1545                      [i + (sstate->state->w + 1) * j] |= 1<<OPP_DLINE(dline); \
1546                }
1547                /* If at least one of a dline in a dot is YES, at most one of
1548                 * the opposite dline to that dot must be YES. */
1549                DOT_DLINES;
1550 #undef HANDLE_DLINE
1551            }
1552        }
1553
1554        /* More obscure per-square operations */
1555        for (j = 0; j < sstate->state->h; ++j) {
1556            for (i = 0; i < sstate->state->w; ++i) {
1557 #define H1(dline, dir1_sq, dir2_sq, a, b, dot_howmany, line_query, line_set)  \
1558                if (sstate->dot_howmany[i+a + (sstate->state->w + 1) * (j+b)] &\
1559                        1<<dline) {                                            \
1560                    t = dir1_sq(sstate->state, i, j);                          \
1561                    if (t == line_query)                                       \
1562                        dir2_sq(sstate->state, i, j) = line_set;               \
1563                    else {                                                     \
1564                        t = dir2_sq(sstate->state, i, j);                      \
1565                        if (t == line_query)                                   \
1566                            dir1_sq(sstate->state, i, j) = line_set;           \
1567                    }                                                          \
1568                }
1569 #define HANDLE_DLINE(dline, dir1_sq, dir2_sq, a, b)                 \
1570                H1(dline, dir1_sq, dir2_sq, a, b, dot_atmostone,     \
1571                   LINE_YES, LINE_NO)
1572                /* If at most one of the DLINE is on, and one is definitely on,
1573                 * set the other to definitely off */
1574                SQUARE_DLINES;
1575 #undef HANDLE_DLINE
1576
1577 #define HANDLE_DLINE(dline, dir1_sq, dir2_sq, a, b)                 \
1578                H1(dline, dir1_sq, dir2_sq, a, b, dot_atleastone,    \
1579                   LINE_NO, LINE_YES)
1580                /* If at least one of the DLINE is on, and one is definitely
1581                 * off, set the other to definitely on */
1582                SQUARE_DLINES;
1583 #undef HANDLE_DLINE
1584 #undef H1
1585
1586                switch (CLUE_AT(sstate->state, i, j)) {
1587                    case '0':
1588                    case '1':
1589 #define HANDLE_DLINE(dline, dir1_sq, dir2_sq, a, b)                          \
1590                        /* At most one of any DLINE can be set */             \
1591                        sstate->dot_atmostone                                 \
1592                          [i+a + (sstate->state->w + 1) * (j+b)] |= 1<<dline; \
1593                        /* This DLINE provides enough YESes to solve the clue */\
1594                        if (sstate->dot_atleastone                            \
1595                              [i+a + (sstate->state->w + 1) * (j+b)] &        \
1596                            1<<dline) {                                       \
1597                            dot_setall_dlines(sstate, OPP_DLINE(dline),       \
1598                                              i+(1-a), j+(1-b),               \
1599                                              LINE_UNKNOWN, LINE_NO);         \
1600                        }
1601                        SQUARE_DLINES;
1602 #undef HANDLE_DLINE
1603                        break;
1604                    case '2':
1605 #define H1(dline, dot_at1one, dot_at2one, a, b)                          \
1606                if (sstate->dot_at1one                                    \
1607                      [i+a + (sstate->state->w + 1) * (j+b)] &            \
1608                    1<<dline) {                                           \
1609                    sstate->dot_at2one                                    \
1610                      [i+(1-a) + (sstate->state->w + 1) * (j+(1-b))] |=   \
1611                        1<<OPP_DLINE(dline);                              \
1612                }
1613 #define HANDLE_DLINE(dline, dir1_sq, dir2_sq, a, b)             \
1614             H1(dline, dot_atleastone, dot_atmostone, a, b);     \
1615             H1(dline, dot_atmostone, dot_atleastone, a, b);
1616                        /* If at least one of one DLINE is set, at most one of
1617                         * the opposing one is and vice versa */
1618                        SQUARE_DLINES;
1619 #undef HANDLE_DLINE
1620 #undef H1
1621                        break;
1622                    case '3':
1623                    case '4':
1624 #define HANDLE_DLINE(dline, dir1_sq, dir2_sq, a, b)                           \
1625                        /* At least one of any DLINE can be set */             \
1626                        sstate->dot_atleastone                                 \
1627                          [i+a + (sstate->state->w + 1) * (j+b)] |= 1<<dline;  \
1628                        /* This DLINE provides enough NOs to solve the clue */ \
1629                        if (sstate->dot_atmostone                              \
1630                              [i+a + (sstate->state->w + 1) * (j+b)] &         \
1631                            1<<dline) {                                        \
1632                            dot_setall_dlines(sstate, OPP_DLINE(dline),        \
1633                                              i+(1-a), j+(1-b),                \
1634                                              LINE_UNKNOWN, LINE_YES);         \
1635                        }
1636                        SQUARE_DLINES;
1637 #undef HANDLE_DLINE
1638                        break;
1639                }
1640            }
1641        }
1642
1643        if (solver_states_equal(sstate, sstate_saved)) {
1644            int edgecount = 0, clues = 0, satclues = 0, sm1clues = 0;
1645            int d;
1646
1647            /*
1648             * Go through the grid and update for all the new edges.
1649             * Since merge_dots() is idempotent, the simplest way to
1650             * do this is just to update for _all_ the edges.
1651             *
1652             * Also, while we're here, we count the edges, count the
1653             * clues, count the satisfied clues, and count the
1654             * satisfied-minus-one clues.
1655             */
1656            for (j = 0; j <= sstate->state->h; ++j) {
1657                for (i = 0; i <= sstate->state->w; ++i) {
1658                    if (RIGHTOF_DOT(sstate->state, i, j) == LINE_YES) {
1659                        merge_dots(sstate, i, j, i+1, j);
1660                        edgecount++;
1661                    }
1662                    if (BELOW_DOT(sstate->state, i, j) == LINE_YES) {
1663                        merge_dots(sstate, i, j, i, j+1);
1664                        edgecount++;
1665                    }
1666
1667                    if (CLUE_AT(sstate->state, i, j) != ' ') {
1668                        int c = CLUE_AT(sstate->state, i, j) - '0';
1669                        int o = square_order(sstate->state, i, j, LINE_YES);
1670                        if (o == c)
1671                            satclues++;
1672                        else if (o == c-1)
1673                            sm1clues++;
1674                        clues++;
1675                    }
1676                }
1677            }
1678
1679            /*
1680             * Now go through looking for LINE_UNKNOWN edges which
1681             * connect two dots that are already in the same
1682             * equivalence class. If we find one, test to see if the
1683             * loop it would create is a solution.
1684             */
1685            for (j = 0; j <= sstate->state->h; ++j) {
1686                for (i = 0; i <= sstate->state->w; ++i) {
1687                    for (d = 0; d < 2; d++) {
1688                        int i2, j2, eqclass, val;
1689
1690                        if (d == 0) {
1691                            if (RIGHTOF_DOT(sstate->state, i, j) !=
1692                                LINE_UNKNOWN)
1693                                continue;
1694                            i2 = i+1;
1695                            j2 = j;
1696                        } else {
1697                            if (BELOW_DOT(sstate->state, i, j) !=
1698                                LINE_UNKNOWN)
1699                                continue;
1700                            i2 = i;
1701                            j2 = j+1;
1702                        }
1703
1704                        eqclass = dsf_canonify(sstate->dotdsf,
1705                                               j * (sstate->state->w+1) + i);
1706                        if (eqclass != dsf_canonify(sstate->dotdsf,
1707                                                    j2 * (sstate->state->w+1) +
1708                                                    i2))
1709                            continue;
1710
1711                        val = LINE_NO;  /* loop is bad until proven otherwise */
1712
1713                        /*
1714                         * This edge would form a loop. Next
1715                         * question: how long would the loop be?
1716                         * Would it equal the total number of edges
1717                         * (plus the one we'd be adding if we added
1718                         * it)?
1719                         */
1720                        if (sstate->looplen[eqclass] == edgecount + 1) {
1721                            int sm1_nearby;
1722                            int cx, cy;
1723
1724                            /*
1725                             * This edge would form a loop which
1726                             * took in all the edges in the entire
1727                             * grid. So now we need to work out
1728                             * whether it would be a valid solution
1729                             * to the puzzle, which means we have to
1730                             * check if it satisfies all the clues.
1731                             * This means that every clue must be
1732                             * either satisfied or satisfied-minus-
1733                             * 1, and also that the number of
1734                             * satisfied-minus-1 clues must be at
1735                             * most two and they must lie on either
1736                             * side of this edge.
1737                             */
1738                            sm1_nearby = 0;
1739                            cx = i - (j2-j);
1740                            cy = j - (i2-i);
1741                            if (CLUE_AT(sstate->state, cx,cy) != ' ' &&
1742                                square_order(sstate->state, cx,cy, LINE_YES) ==
1743                                CLUE_AT(sstate->state, cx,cy) - '0' - 1)
1744                                sm1_nearby++;
1745                            if (CLUE_AT(sstate->state, i, j) != ' ' &&
1746                                square_order(sstate->state, i, j, LINE_YES) ==
1747                                CLUE_AT(sstate->state, i, j) - '0' - 1)
1748                                sm1_nearby++;
1749                            if (sm1clues == sm1_nearby &&
1750                                sm1clues + satclues == clues)
1751                                val = LINE_YES;  /* loop is good! */
1752                        }
1753
1754                        /*
1755                         * Right. Now we know that adding this edge
1756                         * would form a loop, and we know whether
1757                         * that loop would be a viable solution or
1758                         * not.
1759                         *
1760                         * If adding this edge produces a solution,
1761                         * then we know we've found _a_ solution but
1762                         * we don't know that it's _the_ solution -
1763                         * if it were provably the solution then
1764                         * we'd have deduced this edge some time ago
1765                         * without the need to do loop detection. So
1766                         * in this state we return SOLVER_AMBIGUOUS,
1767                         * which has the effect that hitting Solve
1768                         * on a user-provided puzzle will fill in a
1769                         * solution but using the solver to
1770                         * construct new puzzles won't consider this
1771                         * a reasonable deduction for the user to
1772                         * make.
1773                         */
1774                        if (d == 0)
1775                            LV_RIGHTOF_DOT(sstate->state, i, j) = val;
1776                        else
1777                            LV_BELOW_DOT(sstate->state, i, j) = val;
1778                        if (val == LINE_YES) {
1779                            sstate->solver_status = SOLVER_AMBIGUOUS;
1780                            goto finished_loop_checking;
1781                        }
1782                    }
1783                }
1784            }
1785
1786            finished_loop_checking:
1787
1788            RETURN_IF_SOLVED;
1789        }
1790
1791        if (solver_states_equal(sstate, sstate_saved)) {
1792            /* Solver has stopped making progress so we terminate */
1793            free_solver_state(sstate_saved);
1794            break;
1795        }
1796
1797        free_solver_state(sstate_saved);
1798    }
1799
1800    if (sstate->solver_status == SOLVER_SOLVED ||
1801        sstate->solver_status == SOLVER_AMBIGUOUS) {
1802        /* s/LINE_UNKNOWN/LINE_NO/g */
1803        array_setall(sstate->state->hl, LINE_UNKNOWN, LINE_NO,
1804                HL_COUNT(sstate->state));
1805        array_setall(sstate->state->vl, LINE_UNKNOWN, LINE_NO,
1806                VL_COUNT(sstate->state));
1807        return sstate;
1808    }
1809
1810    /* Perform recursive calls */
1811    if (sstate->recursion_remaining) {
1812        sstate->recursion_remaining--;
1813
1814        sstate_saved = dup_solver_state(sstate);
1815
1816        recursive_soln_count = 0;
1817        sstate_rec_solved = NULL;
1818
1819        /* Memory management:
1820         * sstate_saved won't be modified but needs to be freed when we have
1821         * finished with it.
1822         * sstate is expected to contain our 'best' solution by the time we
1823         * finish this section of code.  It's the thing we'll try adding lines
1824         * to, seeing if they make it more solvable.
1825         * If sstate_rec_solved is non-NULL, it will supersede sstate
1826         * eventually.  sstate_tmp should not hold a value persistently.
1827         */
1828
1829        /* NB SOLVER_AMBIGUOUS is like SOLVER_SOLVED except the solver is aware
1830         * of the possibility of additional solutions.  So as soon as we have a
1831         * SOLVER_AMBIGUOUS we can safely propagate it back to our caller, but
1832         * if we get a SOLVER_SOLVED we want to keep trying in case we find
1833         * further solutions and have to mark it ambiguous.
1834         */
1835
1836 #define DO_RECURSIVE_CALL(dir_dot)                                         \
1837        if (dir_dot(sstate->state, i, j) == LINE_UNKNOWN) {                 \
1838            debug(("Trying " #dir_dot " at [%d,%d]\n", i, j));               \
1839            LV_##dir_dot(sstate->state, i, j) = LINE_YES;                   \
1840            sstate_tmp = solve_game_rec(sstate);                            \
1841            switch (sstate_tmp->solver_status) {                            \
1842                case SOLVER_AMBIGUOUS:                                      \
1843                    debug(("Solver ambiguous, returning\n"));                \
1844                    sstate_rec_solved = sstate_tmp;                         \
1845                    goto finished_recursion;                                \
1846                case SOLVER_SOLVED:                                         \
1847                    switch (++recursive_soln_count) {                       \
1848                        case 1:                                             \
1849                            debug(("One solution found\n"));                 \
1850                            sstate_rec_solved = sstate_tmp;                 \
1851                            break;                                          \
1852                        case 2:                                             \
1853                            debug(("Ambiguous solutions found\n"));          \
1854                            free_solver_state(sstate_tmp);                  \
1855                            sstate_rec_solved->solver_status = SOLVER_AMBIGUOUS;\
1856                            goto finished_recursion;                        \
1857                        default:                                            \
1858                            assert(!"recursive_soln_count out of range");   \
1859                            break;                                          \
1860                    }                                                       \
1861                    break;                                                  \
1862                case SOLVER_MISTAKE:                                        \
1863                    debug(("Non-solution found\n"));                         \
1864                    free_solver_state(sstate_tmp);                          \
1865                    free_solver_state(sstate_saved);                        \
1866                    LV_##dir_dot(sstate->state, i, j) = LINE_NO;            \
1867                    goto nonrecursive_solver;                               \
1868                case SOLVER_INCOMPLETE:                                     \
1869                    debug(("Recursive step inconclusive\n"));                \
1870                    free_solver_state(sstate_tmp);                          \
1871                    break;                                                  \
1872            }                                                               \
1873            free_solver_state(sstate);                                      \
1874            sstate = dup_solver_state(sstate_saved);                        \
1875        }
1876
1877        for (j = 0; j < sstate->state->h + 1; ++j) {
1878            for (i = 0; i < sstate->state->w + 1; ++i) {
1879                /* Only perform recursive calls on 'loose ends' */
1880                if (dot_order(sstate->state, i, j, LINE_YES) == 1) {
1881                    if (LEFTOF_DOT(sstate->state, i, j) == LINE_UNKNOWN)
1882                        DO_RECURSIVE_CALL(LEFTOF_DOT);
1883                    if (RIGHTOF_DOT(sstate->state, i, j) == LINE_UNKNOWN)
1884                        DO_RECURSIVE_CALL(RIGHTOF_DOT);
1885                    if (ABOVE_DOT(sstate->state, i, j) == LINE_UNKNOWN)
1886                        DO_RECURSIVE_CALL(ABOVE_DOT);
1887                    if (BELOW_DOT(sstate->state, i, j) == LINE_UNKNOWN)
1888                        DO_RECURSIVE_CALL(BELOW_DOT);
1889                }
1890            }
1891        }
1892
1893 finished_recursion:
1894
1895        if (sstate_rec_solved) {
1896            free_solver_state(sstate);
1897            sstate = sstate_rec_solved;
1898        }
1899    }
1900
1901    return sstate;
1902 }
1903
1904 /* XXX bits of solver that may come in handy one day */
1905 #if 0
1906 #define HANDLE_DLINE(dline, dir1_dot, dir2_dot)                         \
1907                    /* dline from this dot that's entirely unknown must have
1908                     * both lines identical */                           \
1909                    if (dir1_dot(sstate->state, i, j) == LINE_UNKNOWN &&       \
1910                        dir2_dot(sstate->state, i, j) == LINE_UNKNOWN) {       \
1911                        sstate->dline_identical[i + (sstate->state->w + 1) * j] |= \
1912                            1<<dline;                                    \
1913                    } else if (sstate->dline_identical[i +
1914                                                       (sstate->state->w + 1) * j] &\
1915                               1<<dline) {                                   \
1916                        /* If they're identical and one is known do the obvious
1917                         * thing */                                      \
1918                        t = dir1_dot(sstate->state, i, j);                     \
1919                        if (t != LINE_UNKNOWN)                           \
1920                            dir2_dot(sstate->state, i, j) = t;                 \
1921                        else {                                           \
1922                            t = dir2_dot(sstate->state, i, j);                 \
1923                            if (t != LINE_UNKNOWN)                       \
1924                                dir1_dot(sstate->state, i, j) = t;             \
1925                        }                                                \
1926                    }                                                    \
1927                    DOT_DLINES;
1928 #undef HANDLE_DLINE
1929 #endif
1930
1931 #if 0
1932 #define HANDLE_DLINE(dline, dir1_sq, dir2_sq, a, b) \
1933                        if (sstate->dline_identical[i+a +                     \
1934                                                    (sstate->state->w + 1) * (j+b)] &\
1935                            1<<dline) {                                       \
1936                            dir1_sq(sstate->state, i, j) = LINE_YES;                \
1937                            dir2_sq(sstate->state, i, j) = LINE_YES;                \
1938                        }
1939                        /* If two lines are the same they must be on */
1940                        SQUARE_DLINES;
1941 #undef HANDLE_DLINE
1942 #endif
1943
1944
1945 #if 0
1946 #define HANDLE_DLINE(dline, dir1_sq, dir2_sq, a, b) \
1947                if (sstate->dot_atmostone[i+a + (sstate->state->w + 1) * (j+b)] &  \
1948                    1<<dline) {                                   \
1949                    if (square_order(sstate->state, i, j,  LINE_UNKNOWN) - 1 ==  \
1950                        CLUE_AT(sstate->state, i, j) - '0') {      \
1951                        square_setall(sstate->state, i, j, LINE_UNKNOWN, LINE_YES); \
1952                            /* XXX the following may overwrite known data! */ \
1953                        dir1_sq(sstate->state, i, j) = LINE_UNKNOWN;  \
1954                        dir2_sq(sstate->state, i, j) = LINE_UNKNOWN;  \
1955                    }                                  \
1956                }
1957                SQUARE_DLINES;
1958 #undef HANDLE_DLINE
1959 #endif
1960
1961 #if 0
1962 #define HANDLE_DLINE(dline, dir1_sq, dir2_sq, a, b) \
1963                        if (sstate->dline_identical[i+a +
1964                                                    (sstate->state->w + 1) * (j+b)] &\
1965                            1<<dline) {                                       \
1966                            dir1_sq(sstate->state, i, j) = LINE_NO;                 \
1967                            dir2_sq(sstate->state, i, j) = LINE_NO;                 \
1968                        }
1969                        /* If two lines are the same they must be off */
1970                        SQUARE_DLINES;
1971 #undef HANDLE_DLINE
1972 #endif
1973
1974 static char *solve_game(game_state *state, game_state *currstate,
1975                         char *aux, char **error)
1976 {
1977     char *soln = NULL;
1978     solver_state *sstate, *new_sstate;
1979
1980     sstate = new_solver_state(state);
1981     new_sstate = solve_game_rec(sstate);
1982
1983     if (new_sstate->solver_status == SOLVER_SOLVED) {
1984         soln = encode_solve_move(new_sstate->state);
1985     } else if (new_sstate->solver_status == SOLVER_AMBIGUOUS) {
1986         soln = encode_solve_move(new_sstate->state);
1987         /**error = "Solver found ambiguous solutions"; */
1988     } else {
1989         soln = encode_solve_move(new_sstate->state);
1990         /**error = "Solver failed"; */
1991     }
1992
1993     free_solver_state(new_sstate);
1994     free_solver_state(sstate);
1995
1996     return soln;
1997 }
1998
1999 static char *game_text_format(game_state *state)
2000 {
2001     int i, j;
2002     int len;
2003     char *ret, *rp;
2004
2005     len = (2 * state->w + 2) * (2 * state->h + 1);
2006     rp = ret = snewn(len + 1, char);
2007
2008 #define DRAW_HL                          \
2009     switch (ABOVE_SQUARE(state, i, j)) { \
2010         case LINE_YES:                   \
2011             rp += sprintf(rp, " -");     \
2012             break;                       \
2013         case LINE_NO:                    \
2014             rp += sprintf(rp, " x");     \
2015             break;                       \
2016         case LINE_UNKNOWN:               \
2017             rp += sprintf(rp, "  ");     \
2018             break;                       \
2019         default:                         \
2020             assert(!"Illegal line state for HL");\
2021     }
2022
2023 #define DRAW_VL                          \
2024     switch (LEFTOF_SQUARE(state, i, j)) {\
2025         case LINE_YES:                   \
2026             rp += sprintf(rp, "|");      \
2027             break;                       \
2028         case LINE_NO:                    \
2029             rp += sprintf(rp, "x");      \
2030             break;                       \
2031         case LINE_UNKNOWN:               \
2032             rp += sprintf(rp, " ");      \
2033             break;                       \
2034         default:                         \
2035             assert(!"Illegal line state for VL");\
2036     }
2037
2038     for (j = 0; j < state->h; ++j) {
2039         for (i = 0; i < state->w; ++i) {
2040             DRAW_HL;
2041         }
2042         rp += sprintf(rp, " \n");
2043         for (i = 0; i < state->w; ++i) {
2044             DRAW_VL;
2045             rp += sprintf(rp, "%c", (int)(CLUE_AT(state, i, j)));
2046         }
2047         DRAW_VL;
2048         rp += sprintf(rp, "\n");
2049     }
2050     for (i = 0; i < state->w; ++i) {
2051         DRAW_HL;
2052     }
2053     rp += sprintf(rp, " \n");
2054
2055     assert(strlen(ret) == len);
2056     return ret;
2057 }
2058
2059 static game_ui *new_ui(game_state *state)
2060 {
2061     return NULL;
2062 }
2063
2064 static void free_ui(game_ui *ui)
2065 {
2066 }
2067
2068 static char *encode_ui(game_ui *ui)
2069 {
2070     return NULL;
2071 }
2072
2073 static void decode_ui(game_ui *ui, char *encoding)
2074 {
2075 }
2076
2077 static void game_changed_state(game_ui *ui, game_state *oldstate,
2078                                game_state *newstate)
2079 {
2080 }
2081
2082 struct game_drawstate {
2083     int started;
2084     int tilesize;
2085     int flashing;
2086     char *hl, *vl;
2087 };
2088
2089 static char *interpret_move(game_state *state, game_ui *ui, game_drawstate *ds,
2090                             int x, int y, int button)
2091 {
2092     int hl_selected;
2093     int i, j, p, q;
2094     char *ret, buf[80];
2095     char button_char = ' ';
2096     enum line_state old_state;
2097
2098     button &= ~MOD_MASK;
2099
2100     /* Around each line is a diamond-shaped region where points within that
2101      * region are closer to this line than any other.  We assume any click
2102      * within a line's diamond was meant for that line.  It would all be a lot
2103      * simpler if the / and % operators respected modulo arithmetic properly
2104      * for negative numbers. */
2105
2106     x -= BORDER;
2107     y -= BORDER;
2108
2109     /* Get the coordinates of the square the click was in */
2110     i = (x + TILE_SIZE) / TILE_SIZE - 1;
2111     j = (y + TILE_SIZE) / TILE_SIZE - 1;
2112
2113     /* Get the precise position inside square [i,j] */
2114     p = (x + TILE_SIZE) % TILE_SIZE;
2115     q = (y + TILE_SIZE) % TILE_SIZE;
2116
2117     /* After this bit of magic [i,j] will correspond to the point either above
2118      * or to the left of the line selected */
2119     if (p > q) {
2120         if (TILE_SIZE - p > q) {
2121             hl_selected = TRUE;
2122         } else {
2123             hl_selected = FALSE;
2124             ++i;
2125         }
2126     } else {
2127         if (TILE_SIZE - q > p) {
2128             hl_selected = FALSE;
2129         } else {
2130             hl_selected = TRUE;
2131             ++j;
2132         }
2133     }
2134
2135     if (i < 0 || j < 0)
2136         return NULL;
2137
2138     if (hl_selected) {
2139         if (i >= state->w || j >= state->h + 1)
2140             return NULL;
2141     } else {
2142         if (i >= state->w + 1 || j >= state->h)
2143             return NULL;
2144     }
2145
2146     /* I think it's only possible to play this game with mouse clicks, sorry */
2147     /* Maybe will add mouse drag support some time */
2148     if (hl_selected)
2149         old_state = RIGHTOF_DOT(state, i, j);
2150     else
2151         old_state = BELOW_DOT(state, i, j);
2152
2153     switch (button) {
2154         case LEFT_BUTTON:
2155             switch (old_state) {
2156                 case LINE_UNKNOWN:
2157                     button_char = 'y';
2158                     break;
2159                 case LINE_YES:
2160                 case LINE_NO:
2161                     button_char = 'u';
2162                     break;
2163             }
2164             break;
2165         case MIDDLE_BUTTON:
2166             button_char = 'u';
2167             break;
2168         case RIGHT_BUTTON:
2169             switch (old_state) {
2170                 case LINE_UNKNOWN:
2171                     button_char = 'n';
2172                     break;
2173                 case LINE_NO:
2174                 case LINE_YES:
2175                     button_char = 'u';
2176                     break;
2177             }
2178             break;
2179         default:
2180             return NULL;
2181     }
2182
2183
2184     sprintf(buf, "%d,%d%c%c", i, j, (int)(hl_selected ? 'h' : 'v'), (int)button_char);
2185     ret = dupstr(buf);
2186
2187     return ret;
2188 }
2189
2190 static game_state *execute_move(game_state *state, char *move)
2191 {
2192     int i, j;
2193     game_state *newstate = dup_game(state);
2194
2195     if (move[0] == 'S') {
2196         move++;
2197         newstate->cheated = TRUE;
2198     }
2199
2200     while (*move) {
2201         i = atoi(move);
2202         move = strchr(move, ',');
2203         if (!move)
2204             goto fail;
2205         j = atoi(++move);
2206         move += strspn(move, "1234567890");
2207         switch (*(move++)) {
2208             case 'h':
2209                 if (i >= newstate->w || j > newstate->h)
2210                     goto fail;
2211                 switch (*(move++)) {
2212                     case 'y':
2213                         LV_RIGHTOF_DOT(newstate, i, j) = LINE_YES;
2214                         break;
2215                     case 'n':
2216                         LV_RIGHTOF_DOT(newstate, i, j) = LINE_NO;
2217                         break;
2218                     case 'u':
2219                         LV_RIGHTOF_DOT(newstate, i, j) = LINE_UNKNOWN;
2220                         break;
2221                     default:
2222                         goto fail;
2223                 }
2224                 break;
2225             case 'v':
2226                 if (i > newstate->w || j >= newstate->h)
2227                     goto fail;
2228                 switch (*(move++)) {
2229                     case 'y':
2230                         LV_BELOW_DOT(newstate, i, j) = LINE_YES;
2231                         break;
2232                     case 'n':
2233                         LV_BELOW_DOT(newstate, i, j) = LINE_NO;
2234                         break;
2235                     case 'u':
2236                         LV_BELOW_DOT(newstate, i, j) = LINE_UNKNOWN;
2237                         break;
2238                     default:
2239                         goto fail;
2240                 }
2241                 break;
2242             default:
2243                 goto fail;
2244         }
2245     }
2246
2247     /*
2248      * Check for completion.
2249      */
2250     i = 0;                             /* placate optimiser */
2251     for (j = 0; j <= newstate->h; j++) {
2252         for (i = 0; i < newstate->w; i++)
2253             if (LV_RIGHTOF_DOT(newstate, i, j) == LINE_YES)
2254                 break;
2255         if (i < newstate->w)
2256             break;
2257     }
2258     if (j <= newstate->h) {
2259         int prevdir = 'R';
2260         int x = i, y = j;
2261         int looplen, count;
2262
2263         /*
2264          * We've found a horizontal edge at (i,j). Follow it round
2265          * to see if it's part of a loop.
2266          */
2267         looplen = 0;
2268         while (1) {
2269             int order = dot_order(newstate, x, y, LINE_YES);
2270             if (order != 2)
2271                 goto completion_check_done;
2272
2273             if (LEFTOF_DOT(newstate, x, y) == LINE_YES && prevdir != 'L') {
2274                 x--;
2275                 prevdir = 'R';
2276             } else if (RIGHTOF_DOT(newstate, x, y) == LINE_YES &&
2277                        prevdir != 'R') {
2278                 x++;
2279                 prevdir = 'L';
2280             } else if (ABOVE_DOT(newstate, x, y) == LINE_YES &&
2281                        prevdir != 'U') {
2282                 y--;
2283                 prevdir = 'D';
2284             } else if (BELOW_DOT(newstate, x, y) == LINE_YES &&
2285                        prevdir != 'D') {
2286                 y++;
2287                 prevdir = 'U';
2288             } else {
2289                 assert(!"Can't happen");   /* dot_order guarantees success */
2290             }
2291
2292             looplen++;
2293
2294             if (x == i && y == j)
2295                 break;
2296         }
2297
2298         if (x != i || y != j || looplen == 0)
2299             goto completion_check_done;
2300
2301         /*
2302          * We've traced our way round a loop, and we know how many
2303          * line segments were involved. Count _all_ the line
2304          * segments in the grid, to see if the loop includes them
2305          * all.
2306          */
2307         count = 0;
2308         for (j = 0; j <= newstate->h; j++)
2309             for (i = 0; i <= newstate->w; i++)
2310                 count += ((RIGHTOF_DOT(newstate, i, j) == LINE_YES) +
2311                           (BELOW_DOT(newstate, i, j) == LINE_YES));
2312         assert(count >= looplen);
2313         if (count != looplen)
2314             goto completion_check_done;
2315
2316         /*
2317          * The grid contains one closed loop and nothing else.
2318          * Check that all the clues are satisfied.
2319          */
2320         for (j = 0; j < newstate->h; ++j) {
2321             for (i = 0; i < newstate->w; ++i) {
2322                 int n = CLUE_AT(newstate, i, j);
2323                 if (n != ' ') {
2324                     if (square_order(newstate, i, j, LINE_YES) != n - '0') {
2325                         goto completion_check_done;
2326                     }
2327                 }
2328             }
2329         }
2330
2331         /*
2332          * Completed!
2333          */
2334         newstate->solved = TRUE;
2335     }
2336
2337 completion_check_done:
2338     return newstate;
2339
2340 fail:
2341     free_game(newstate);
2342     return NULL;
2343 }
2344
2345 /* ----------------------------------------------------------------------
2346  * Drawing routines.
2347  */
2348
2349 #define SIZE(d) ((d) * TILE_SIZE + 2 * BORDER + 1)
2350
2351 static void game_compute_size(game_params *params, int tilesize,
2352                               int *x, int *y)
2353 {
2354     struct { int tilesize; } ads, *ds = &ads;
2355     ads.tilesize = tilesize;
2356
2357     *x = SIZE(params->w);
2358     *y = SIZE(params->h);
2359 }
2360
2361 static void game_set_size(drawing *dr, game_drawstate *ds,
2362                           game_params *params, int tilesize)
2363 {
2364     ds->tilesize = tilesize;
2365 }
2366
2367 static float *game_colours(frontend *fe, game_state *state, 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     *ncolours = NCOLOURS;
2382     return ret;
2383 }
2384
2385 static game_drawstate *game_new_drawstate(drawing *dr, game_state *state)
2386 {
2387     struct game_drawstate *ds = snew(struct game_drawstate);
2388
2389     ds->tilesize = 0;
2390     ds->started = 0;
2391     ds->hl = snewn(HL_COUNT(state), char);
2392     ds->vl = snewn(VL_COUNT(state), char);
2393     ds->flashing = 0;
2394
2395     memset(ds->hl, LINE_UNKNOWN, HL_COUNT(state));
2396     memset(ds->vl, LINE_UNKNOWN, VL_COUNT(state));
2397
2398     return ds;
2399 }
2400
2401 static void game_free_drawstate(drawing *dr, game_drawstate *ds)
2402 {
2403     sfree(ds->hl);
2404     sfree(ds->vl);
2405     sfree(ds);
2406 }
2407
2408 static void game_redraw(drawing *dr, game_drawstate *ds, game_state *oldstate,
2409                         game_state *state, int dir, game_ui *ui,
2410                         float animtime, float flashtime)
2411 {
2412     int i, j;
2413     int w = state->w, h = state->h;
2414     char c[2];
2415     int line_colour, flash_changed;
2416
2417     if (!ds->started) {
2418         /*
2419          * The initial contents of the window are not guaranteed and
2420          * can vary with front ends. To be on the safe side, all games
2421          * should start by drawing a big background-colour rectangle
2422          * covering the whole window.
2423          */
2424         draw_rect(dr, 0, 0, SIZE(state->w), SIZE(state->h), COL_BACKGROUND);
2425
2426         /* Draw dots */
2427         for (j = 0; j < h + 1; ++j) {
2428             for (i = 0; i < w + 1; ++i) {
2429                 draw_rect(dr,
2430                           BORDER + i * TILE_SIZE - LINEWIDTH/2,
2431                           BORDER + j * TILE_SIZE - LINEWIDTH/2,
2432                           LINEWIDTH, LINEWIDTH, COL_FOREGROUND);
2433             }
2434         }
2435
2436         /* Draw clues */
2437         for (j = 0; j < h; ++j) {
2438             for (i = 0; i < w; ++i) {
2439                 c[0] = CLUE_AT(state, i, j);
2440                 c[1] = '\0';
2441                 draw_text(dr,
2442                           BORDER + i * TILE_SIZE + TILE_SIZE/2,
2443                           BORDER + j * TILE_SIZE + TILE_SIZE/2,
2444                           FONT_VARIABLE, TILE_SIZE/2,
2445                           ALIGN_VCENTRE | ALIGN_HCENTRE, COL_FOREGROUND, c);
2446             }
2447         }
2448         draw_update(dr, 0, 0,
2449                     state->w * TILE_SIZE + 2*BORDER + 1,
2450                     state->h * TILE_SIZE + 2*BORDER + 1);
2451         ds->started = TRUE;
2452     }
2453
2454     if (flashtime > 0 &&
2455         (flashtime <= FLASH_TIME/3 ||
2456          flashtime >= FLASH_TIME*2/3)) {
2457         flash_changed = !ds->flashing;
2458         ds->flashing = TRUE;
2459         line_colour = COL_HIGHLIGHT;
2460     } else {
2461         flash_changed = ds->flashing;
2462         ds->flashing = FALSE;
2463         line_colour = COL_FOREGROUND;
2464     }
2465
2466 #define CROSS_SIZE (3 * LINEWIDTH / 2)
2467
2468 #define CLEAR_VL(i, j) do {                                                \
2469                            draw_rect(dr,                                   \
2470                                  BORDER + i * TILE_SIZE - CROSS_SIZE,      \
2471                                  BORDER + j * TILE_SIZE + LINEWIDTH - LINEWIDTH/2,     \
2472                                  CROSS_SIZE * 2,                           \
2473                                  TILE_SIZE - LINEWIDTH,                    \
2474                                  COL_BACKGROUND);                          \
2475                            draw_update(dr,                                 \
2476                                        BORDER + i * TILE_SIZE - CROSS_SIZE, \
2477                                        BORDER + j * TILE_SIZE - CROSS_SIZE, \
2478                                        CROSS_SIZE*2,                       \
2479                                        TILE_SIZE + CROSS_SIZE*2);          \
2480                         } while (0)
2481
2482 #define CLEAR_HL(i, j) do {                                                \
2483                            draw_rect(dr,                                   \
2484                                  BORDER + i * TILE_SIZE + LINEWIDTH - LINEWIDTH/2,     \
2485                                  BORDER + j * TILE_SIZE - CROSS_SIZE,      \
2486                                  TILE_SIZE - LINEWIDTH,                    \
2487                                  CROSS_SIZE * 2,                           \
2488                                  COL_BACKGROUND);                          \
2489                            draw_update(dr,                                 \
2490                                        BORDER + i * TILE_SIZE - CROSS_SIZE, \
2491                                        BORDER + j * TILE_SIZE - CROSS_SIZE, \
2492                                        TILE_SIZE + CROSS_SIZE*2,           \
2493                                        CROSS_SIZE*2);                      \
2494                         } while (0)
2495
2496     /* Vertical lines */
2497     for (j = 0; j < h; ++j) {
2498         for (i = 0; i < w + 1; ++i) {
2499             switch (BELOW_DOT(state, i, j)) {
2500                 case LINE_UNKNOWN:
2501                     if (ds->vl[i + (w + 1) * j] != BELOW_DOT(state, i, j)) {
2502                         CLEAR_VL(i, j);
2503                     }
2504                     break;
2505                 case LINE_YES:
2506                     if (ds->vl[i + (w + 1) * j] != BELOW_DOT(state, i, j) ||
2507                         flash_changed) {
2508                         CLEAR_VL(i, j);
2509                         draw_rect(dr,
2510                                   BORDER + i * TILE_SIZE - LINEWIDTH/2,
2511                                   BORDER + j * TILE_SIZE + LINEWIDTH - LINEWIDTH/2,
2512                                   LINEWIDTH, TILE_SIZE - LINEWIDTH,
2513                                   line_colour);
2514                     }
2515                     break;
2516                 case LINE_NO:
2517                     if (ds->vl[i + (w + 1) * j] != BELOW_DOT(state, i, j)) {
2518                         CLEAR_VL(i, j);
2519                         draw_line(dr,
2520                                  BORDER + i * TILE_SIZE - CROSS_SIZE,
2521                                  BORDER + j * TILE_SIZE + TILE_SIZE/2 - CROSS_SIZE,
2522                                  BORDER + i * TILE_SIZE + CROSS_SIZE - 1,
2523                                  BORDER + j * TILE_SIZE + TILE_SIZE/2 + CROSS_SIZE - 1,
2524                                   COL_FOREGROUND);
2525                         draw_line(dr,
2526                                  BORDER + i * TILE_SIZE + CROSS_SIZE - 1,
2527                                  BORDER + j * TILE_SIZE + TILE_SIZE/2 - CROSS_SIZE,
2528                                  BORDER + i * TILE_SIZE - CROSS_SIZE,
2529                                  BORDER + j * TILE_SIZE + TILE_SIZE/2 + CROSS_SIZE - 1,
2530                                   COL_FOREGROUND);
2531                     }
2532                     break;
2533             }
2534             ds->vl[i + (w + 1) * j] = BELOW_DOT(state, i, j);
2535         }
2536     }
2537
2538     /* Horizontal lines */
2539     for (j = 0; j < h + 1; ++j) {
2540         for (i = 0; i < w; ++i) {
2541             switch (RIGHTOF_DOT(state, i, j)) {
2542                 case LINE_UNKNOWN:
2543                     if (ds->hl[i + w * j] != RIGHTOF_DOT(state, i, j)) {
2544                         CLEAR_HL(i, j);
2545                 }
2546                         break;
2547                 case LINE_YES:
2548                     if (ds->hl[i + w * j] != RIGHTOF_DOT(state, i, j) ||
2549                         flash_changed) {
2550                         CLEAR_HL(i, j);
2551                         draw_rect(dr,
2552                                   BORDER + i * TILE_SIZE + LINEWIDTH - LINEWIDTH/2,
2553                                   BORDER + j * TILE_SIZE - LINEWIDTH/2,
2554                                   TILE_SIZE - LINEWIDTH, LINEWIDTH,
2555                                   line_colour);
2556                         break;
2557                     }
2558                 case LINE_NO:
2559                     if (ds->hl[i + w * j] != RIGHTOF_DOT(state, i, j)) {
2560                         CLEAR_HL(i, j);
2561                         draw_line(dr,
2562                                  BORDER + i * TILE_SIZE + TILE_SIZE/2 - CROSS_SIZE,
2563                                  BORDER + j * TILE_SIZE + CROSS_SIZE - 1,
2564                                  BORDER + i * TILE_SIZE + TILE_SIZE/2 + CROSS_SIZE - 1,
2565                                  BORDER + j * TILE_SIZE - CROSS_SIZE,
2566                                   COL_FOREGROUND);
2567                         draw_line(dr,
2568                                  BORDER + i * TILE_SIZE + TILE_SIZE/2 - CROSS_SIZE,
2569                                  BORDER + j * TILE_SIZE - CROSS_SIZE,
2570                                  BORDER + i * TILE_SIZE + TILE_SIZE/2 + CROSS_SIZE - 1,
2571                                  BORDER + j * TILE_SIZE + CROSS_SIZE - 1,
2572                                   COL_FOREGROUND);
2573                         break;
2574                     }
2575             }
2576             ds->hl[i + w * j] = RIGHTOF_DOT(state, i, j);
2577         }
2578     }
2579 }
2580
2581 static float game_anim_length(game_state *oldstate, game_state *newstate,
2582                               int dir, game_ui *ui)
2583 {
2584     return 0.0F;
2585 }
2586
2587 static float game_flash_length(game_state *oldstate, game_state *newstate,
2588                                int dir, game_ui *ui)
2589 {
2590     if (!oldstate->solved  &&  newstate->solved &&
2591         !oldstate->cheated && !newstate->cheated) {
2592         return FLASH_TIME;
2593     }
2594
2595     return 0.0F;
2596 }
2597
2598 static int game_wants_statusbar(void)
2599 {
2600     return FALSE;
2601 }
2602
2603 static int game_timing_state(game_state *state, game_ui *ui)
2604 {
2605     return TRUE;
2606 }
2607
2608 static void game_print_size(game_params *params, float *x, float *y)
2609 {
2610     int pw, ph;
2611
2612     /*
2613      * I'll use 7mm squares by default.
2614      */
2615     game_compute_size(params, 700, &pw, &ph);
2616     *x = pw / 100.0F;
2617     *y = ph / 100.0F;
2618 }
2619
2620 static void game_print(drawing *dr, game_state *state, int tilesize)
2621 {
2622     int w = state->w, h = state->h;
2623     int ink = print_mono_colour(dr, 0);
2624     int x, y;
2625     game_drawstate ads, *ds = &ads;
2626     ds->tilesize = tilesize;
2627
2628     /*
2629      * Dots. I'll deliberately make the dots a bit wider than the
2630      * lines, so you can still see them. (And also because it's
2631      * annoyingly tricky to make them _exactly_ the same size...)
2632      */
2633     for (y = 0; y <= h; y++)
2634         for (x = 0; x <= w; x++)
2635             draw_circle(dr, BORDER + x * TILE_SIZE, BORDER + y * TILE_SIZE,
2636                         LINEWIDTH, ink, ink);
2637
2638     /*
2639      * Clues.
2640      */
2641     for (y = 0; y < h; y++)
2642         for (x = 0; x < w; x++)
2643             if (CLUE_AT(state, x, y) != ' ') {
2644                 char c[2];
2645
2646                 c[0] = CLUE_AT(state, x, y);
2647                 c[1] = '\0';
2648                 draw_text(dr,
2649                           BORDER + x * TILE_SIZE + TILE_SIZE/2,
2650                           BORDER + y * TILE_SIZE + TILE_SIZE/2,
2651                           FONT_VARIABLE, TILE_SIZE/2,
2652                           ALIGN_VCENTRE | ALIGN_HCENTRE, ink, c);
2653             }
2654
2655     /*
2656      * Lines. (At the moment, I'm not bothering with crosses.)
2657      */
2658     for (y = 0; y <= h; y++)
2659         for (x = 0; x < w; x++)
2660             if (RIGHTOF_DOT(state, x, y) == LINE_YES)
2661                 draw_rect(dr, BORDER + x * TILE_SIZE,
2662                           BORDER + y * TILE_SIZE - LINEWIDTH/2,
2663                           TILE_SIZE, (LINEWIDTH/2) * 2 + 1, ink);
2664     for (y = 0; y < h; y++)
2665         for (x = 0; x <= w; x++)
2666             if (BELOW_DOT(state, x, y) == LINE_YES)
2667                 draw_rect(dr, BORDER + x * TILE_SIZE - LINEWIDTH/2,
2668                           BORDER + y * TILE_SIZE,
2669                           (LINEWIDTH/2) * 2 + 1, TILE_SIZE, ink);
2670 }
2671
2672 #ifdef COMBINED
2673 #define thegame loopy
2674 #endif
2675
2676 const struct game thegame = {
2677     "Loopy", "games.loopy",
2678     default_params,
2679     game_fetch_preset,
2680     decode_params,
2681     encode_params,
2682     free_params,
2683     dup_params,
2684     TRUE, game_configure, custom_params,
2685     validate_params,
2686     new_game_desc,
2687     validate_desc,
2688     new_game,
2689     dup_game,
2690     free_game,
2691     1, solve_game,
2692     TRUE, game_text_format,
2693     new_ui,
2694     free_ui,
2695     encode_ui,
2696     decode_ui,
2697     game_changed_state,
2698     interpret_move,
2699     execute_move,
2700     PREFERRED_TILE_SIZE, game_compute_size, game_set_size,
2701     game_colours,
2702     game_new_drawstate,
2703     game_free_drawstate,
2704     game_redraw,
2705     game_anim_length,
2706     game_flash_length,
2707     TRUE, FALSE, game_print_size, game_print,
2708     game_wants_statusbar,
2709     FALSE, game_timing_state,
2710     0,                                       /* mouse_priorities */
2711 };