Implemented a couple more reasoning modes for Extreme difficulty
[sgt/puzzles] / map.c
diff --git a/map.c b/map.c
index 5a9bf5e..45d6329 100644 (file)
--- a/map.c
+++ b/map.c
@@ -5,7 +5,6 @@
 /*
  * TODO:
  * 
- *  - error highlighting
  *  - clue marking
  *  - more solver brains?
  *  - better four-colouring algorithm?
@@ -43,7 +42,8 @@ static float flash_length;
  */
 #define DIFFLIST(A) \
     A(EASY,Easy,e) \
-    A(NORMAL,Normal,n)
+    A(NORMAL,Normal,n) \
+    A(RECURSE,Unreasonable,u)
 #define ENUM(upper,title,lower) DIFF_ ## upper,
 #define TITLE(upper,title,lower) #title,
 #define ENCODE(upper,title,lower) #lower
@@ -59,6 +59,7 @@ enum {
     COL_BACKGROUND,
     COL_GRID,
     COL_0, COL_1, COL_2, COL_3,
+    COL_ERROR, COL_ERRTEXT,
     NCOLOURS
 };
 
@@ -73,6 +74,7 @@ struct map {
     int n;
     int ngraph;
     int *immutable;
+    int *edgex, *edgey;                       /* positions of a point on each edge */
 };
 
 struct game_state {
@@ -607,7 +609,7 @@ static int gengraph(int w, int h, int n, int *map, int *graph)
     return j;
 }
 
-static int graph_adjacent(int *graph, int n, int ngraph, int i, int j)
+static int graph_edge_index(int *graph, int n, int ngraph, int i, int j)
 {
     int v = i*n+j;
     int top, bot, mid;
@@ -617,15 +619,18 @@ static int graph_adjacent(int *graph, int n, int ngraph, int i, int j)
     while (top - bot > 1) {
        mid = (top + bot) / 2;
        if (graph[mid] == v)
-           return TRUE;
+           return mid;
        else if (graph[mid] < v)
            bot = mid;
        else
            top = mid;
     }
-    return FALSE;
+    return -1;
 }
 
+#define graph_adjacent(graph, n, ngraph, i, j) \
+    (graph_edge_index((graph), (n), (ngraph), (i), (j)) >= 0)
+
 static int graph_vertex_start(int *graph, int n, int ngraph, int i)
 {
     int v = i*n;
@@ -785,6 +790,7 @@ struct solver_scratch {
     int *graph;
     int n;
     int ngraph;
+    int depth;
 };
 
 static struct solver_scratch *new_scratch(int *graph, int n, int ngraph)
@@ -796,6 +802,7 @@ static struct solver_scratch *new_scratch(int *graph, int n, int ngraph)
     sc->n = n;
     sc->ngraph = ngraph;
     sc->possible = snewn(n, unsigned char);
+    sc->depth = 0;
 
     return sc;
 }
@@ -953,13 +960,103 @@ static int map_solver(struct solver_scratch *sc,
     }
 
     /*
-     * We've run out of things to deduce. See if we've got the lot.
+     * See if we've got a complete solution, and return if so.
      */
     for (i = 0; i < n; i++)
        if (colouring[i] < 0)
-           return 2;
+            break;
+    if (i == n)
+        return 1;                      /* success! */
+
+    /*
+     * If recursion is not permissible, we now give up.
+     */
+    if (difficulty < DIFF_RECURSE)
+        return 2;                      /* unable to complete */
+
+    /*
+     * Now we've got to do something recursive. So first hunt for a
+     * currently-most-constrained region.
+     */
+    {
+        int best, bestc;
+        struct solver_scratch *rsc;
+        int *subcolouring, *origcolouring;
+        int ret, subret;
+        int we_already_got_one;
+
+        best = -1;
+        bestc = FIVE;
+
+        for (i = 0; i < n; i++) if (colouring[i] < 0) {
+            int p = sc->possible[i];
+            enum { compile_time_assertion = 1 / (FOUR <= 4) };
+            int c;
+
+            /* Count the set bits. */
+            c = (p & 5) + ((p >> 1) & 5);
+            c = (c & 3) + ((c >> 2) & 3);
+            assert(c > 1);             /* or colouring[i] would be >= 0 */
+
+            if (c < bestc) {
+                best = i;
+                bestc = c;
+            }
+        }
+
+        assert(best >= 0);             /* or we'd be solved already */
+
+        /*
+         * Now iterate over the possible colours for this region.
+         */
+        rsc = new_scratch(graph, n, ngraph);
+        rsc->depth = sc->depth + 1;
+        origcolouring = snewn(n, int);
+        memcpy(origcolouring, colouring, n * sizeof(int));
+        subcolouring = snewn(n, int);
+        we_already_got_one = FALSE;
+        ret = 0;
+
+        for (i = 0; i < FOUR; i++) {
+            if (!(sc->possible[best] & (1 << i)))
+                continue;
+
+            memcpy(subcolouring, origcolouring, n * sizeof(int));
+            subcolouring[best] = i;
+            subret = map_solver(rsc, graph, n, ngraph,
+                                subcolouring, difficulty);
 
-    return 1;                         /* success! */
+            /*
+             * If this possibility turned up more than one valid
+             * solution, or if it turned up one and we already had
+             * one, we're definitely ambiguous.
+             */
+            if (subret == 2 || (subret == 1 && we_already_got_one)) {
+                ret = 2;
+                break;
+            }
+
+            /*
+             * If this possibility turned up one valid solution and
+             * it's the first we've seen, copy it into the output.
+             */
+            if (subret == 1) {
+                memcpy(colouring, subcolouring, n * sizeof(int));
+                we_already_got_one = TRUE;
+                ret = 1;
+            }
+
+            /*
+             * Otherwise, this guess led to a contradiction, so we
+             * do nothing.
+             */
+        }
+
+        sfree(subcolouring);
+        free_scratch(rsc);
+
+        return ret;
+    }
 }
 
 /* ----------------------------------------------------------------------
@@ -969,7 +1066,7 @@ static int map_solver(struct solver_scratch *sc,
 static char *new_game_desc(game_params *params, random_state *rs,
                           char **aux, int interactive)
 {
-    struct solver_scratch *sc;
+    struct solver_scratch *sc = NULL;
     int *map, *graph, ngraph, *colouring, *colouring2, *regions;
     int i, j, w, h, n, solveret, cfreq[FOUR];
     int wh;
@@ -1103,6 +1200,7 @@ static char *new_game_desc(game_params *params, random_state *rs,
 
         shuffle(regions, n, sizeof(*regions), rs);
 
+        if (sc) free_scratch(sc);
         sc = new_scratch(graph, n, ngraph);
 
         for (i = 0; i < n; i++) {
@@ -1141,8 +1239,8 @@ static char *new_game_desc(game_params *params, random_state *rs,
          * Finally, check that the puzzle is _at least_ as hard as
          * required, and indeed that it isn't already solved.
          * (Calling map_solver with negative difficulty ensures the
-         * latter - if a solver which _does nothing_ can't solve
-         * it, it's too easy!)
+         * latter - if a solver which _does nothing_ can solve it,
+         * it's too easy!)
          */
         memcpy(colouring2, colouring, n*sizeof(int));
         if (map_solver(sc, graph, n, ngraph, colouring2,
@@ -1150,7 +1248,7 @@ static char *new_game_desc(game_params *params, random_state *rs,
            /*
             * Drop minimum difficulty if necessary.
             */
-           if (mindiff > 0 && (n < 9 || n > 3*wh/2)) {
+           if (mindiff > 0 && (n < 9 || n > 2*wh/3)) {
                if (tries-- <= 0)
                    mindiff = 0;       /* give up and go for Easy */
            }
@@ -1388,7 +1486,7 @@ static char *validate_desc(game_params *params, char *desc)
     return NULL;
 }
 
-static game_state *new_game(midend_data *me, game_params *params, char *desc)
+static game_state *new_game(midend *me, game_params *params, char *desc)
 {
     int w = params->w, h = params->h, wh = w*h, n = params->n;
     int i, pos;
@@ -1501,6 +1599,198 @@ static game_state *new_game(midend_data *me, game_params *params, char *desc)
         random_free(rs);
     }
 
+    /*
+     * Analyse the map to find a canonical line segment
+     * corresponding to each edge. These are where we'll eventually
+     * put error markers.
+     */
+    {
+       int *bestx, *besty, *an, pass;
+       float *ax, *ay, *best;
+
+       ax = snewn(state->map->ngraph, float);
+       ay = snewn(state->map->ngraph, float);
+       an = snewn(state->map->ngraph, int);
+       bestx = snewn(state->map->ngraph, int);
+       besty = snewn(state->map->ngraph, int);
+       best = snewn(state->map->ngraph, float);
+
+       for (i = 0; i < state->map->ngraph; i++) {
+           bestx[i] = besty[i] = -1;
+           best[i] = 2*(w+h)+1;
+           ax[i] = ay[i] = 0.0F;
+           an[i] = 0;
+       }
+
+       /*
+        * We make two passes over the map, finding all the line
+        * segments separating regions. In the first pass, we
+        * compute the _average_ x and y coordinate of all the line
+        * segments separating each pair of regions; in the second
+        * pass, for each such average point, we find the line
+        * segment closest to it and call that canonical.
+        * 
+        * Line segments are considered to have coordinates in
+        * their centre. Thus, at least one coordinate for any line
+        * segment is always something-and-a-half; so we store our
+        * coordinates as twice their normal value.
+        */
+       for (pass = 0; pass < 2; pass++) {
+           int x, y;
+
+           for (y = 0; y < h; y++)
+               for (x = 0; x < w; x++) {
+                   int ex[4], ey[4], ea[4], eb[4], en = 0;
+
+                   /*
+                    * Look for an edge to the right of this
+                    * square, an edge below it, and an edge in the
+                    * middle of it. Also look to see if the point
+                    * at the bottom right of this square is on an
+                    * edge (and isn't a place where more than two
+                    * regions meet).
+                    */
+                   if (x+1 < w) {
+                       /* right edge */
+                       ea[en] = state->map->map[RE * wh + y*w+x];
+                       eb[en] = state->map->map[LE * wh + y*w+(x+1)];
+                       if (ea[en] != eb[en]) {
+                           ex[en] = (x+1)*2;
+                           ey[en] = y*2+1;
+                           en++;
+                       }
+                   }
+                   if (y+1 < h) {
+                       /* bottom edge */
+                       ea[en] = state->map->map[BE * wh + y*w+x];
+                       eb[en] = state->map->map[TE * wh + (y+1)*w+x];
+                       if (ea[en] != eb[en]) {
+                           ex[en] = x*2+1;
+                           ey[en] = (y+1)*2;
+                           en++;
+                       }
+                   }
+                   /* diagonal edge */
+                   ea[en] = state->map->map[TE * wh + y*w+x];
+                   eb[en] = state->map->map[BE * wh + y*w+x];
+                   if (ea[en] != eb[en]) {
+                       ex[en] = x*2+1;
+                       ey[en] = y*2+1;
+                       en++;
+                   }
+                   if (x+1 < w && y+1 < h) {
+                       /* bottom right corner */
+                       int oct[8], othercol, nchanges;
+                       oct[0] = state->map->map[RE * wh + y*w+x];
+                       oct[1] = state->map->map[LE * wh + y*w+(x+1)];
+                       oct[2] = state->map->map[BE * wh + y*w+(x+1)];
+                       oct[3] = state->map->map[TE * wh + (y+1)*w+(x+1)];
+                       oct[4] = state->map->map[LE * wh + (y+1)*w+(x+1)];
+                       oct[5] = state->map->map[RE * wh + (y+1)*w+x];
+                       oct[6] = state->map->map[TE * wh + (y+1)*w+x];
+                       oct[7] = state->map->map[BE * wh + y*w+x];
+
+                       othercol = -1;
+                       nchanges = 0;
+                       for (i = 0; i < 8; i++) {
+                           if (oct[i] != oct[0]) {
+                               if (othercol < 0)
+                                   othercol = oct[i];
+                               else if (othercol != oct[i])
+                                   break;   /* three colours at this point */
+                           }
+                           if (oct[i] != oct[(i+1) & 7])
+                               nchanges++;
+                       }
+
+                       /*
+                        * Now if there are exactly two regions at
+                        * this point (not one, and not three or
+                        * more), and only two changes around the
+                        * loop, then this is a valid place to put
+                        * an error marker.
+                        */
+                       if (i == 8 && othercol >= 0 && nchanges == 2) {
+                           ea[en] = oct[0];
+                           eb[en] = othercol;
+                           ex[en] = (x+1)*2;
+                           ey[en] = (y+1)*2;
+                           en++;
+                       }
+                   }
+
+                   /*
+                    * Now process the edges we've found, one by
+                    * one.
+                    */
+                   for (i = 0; i < en; i++) {
+                       int emin = min(ea[i], eb[i]);
+                       int emax = max(ea[i], eb[i]);
+                       int gindex = 
+                           graph_edge_index(state->map->graph, n,
+                                            state->map->ngraph, emin, emax);
+
+                       assert(gindex >= 0);
+
+                       if (pass == 0) {
+                           /*
+                            * In pass 0, accumulate the values
+                            * we'll use to compute the average
+                            * positions.
+                            */
+                           ax[gindex] += ex[i];
+                           ay[gindex] += ey[i];
+                           an[gindex] += 1.0F;
+                       } else {
+                           /*
+                            * In pass 1, work out whether this
+                            * point is closer to the average than
+                            * the last one we've seen.
+                            */
+                           float dx, dy, d;
+
+                           assert(an[gindex] > 0);
+                           dx = ex[i] - ax[gindex];
+                           dy = ey[i] - ay[gindex];
+                           d = sqrt(dx*dx + dy*dy);
+                           if (d < best[gindex]) {
+                               best[gindex] = d;
+                               bestx[gindex] = ex[i];
+                               besty[gindex] = ey[i];
+                           }
+                       }
+                   }
+               }
+
+           if (pass == 0) {
+               for (i = 0; i < state->map->ngraph; i++)
+                   if (an[i] > 0) {
+                       ax[i] /= an[i];
+                       ay[i] /= an[i];
+                   }
+           }
+       }
+
+       state->map->edgex = bestx;
+       state->map->edgey = besty;
+
+       for (i = 0; i < state->map->ngraph; i++)
+           if (state->map->edgex[i] < 0) {
+               /* Find the other representation of this edge. */
+               int e = state->map->graph[i];
+               int iprime = graph_edge_index(state->map->graph, n,
+                                             state->map->ngraph, e%n, e/n);
+               assert(state->map->edgex[iprime] >= 0);
+               state->map->edgex[i] = state->map->edgex[iprime];
+               state->map->edgey[i] = state->map->edgey[iprime];
+           }
+
+       sfree(ax);
+       sfree(ay);
+       sfree(an);
+       sfree(best);
+    }
+
     return state;
 }
 
@@ -1525,6 +1815,8 @@ static void free_game(game_state *state)
        sfree(state->map->map);
        sfree(state->map->graph);
        sfree(state->map->immutable);
+       sfree(state->map->edgex);
+       sfree(state->map->edgey);
        sfree(state->map);
     }
     sfree(state->colouring);
@@ -1562,8 +1854,10 @@ static char *solve_game(game_state *state, game_state *currstate,
            return NULL;
        }
 
-       retlen = retsize = 0;
-       ret = NULL;
+        retsize = 64;
+        ret = snewn(retsize, char);
+        strcpy(ret, "S");
+        retlen = 1;
 
        for (i = 0; i < state->map->n; i++) {
             int len;
@@ -1573,8 +1867,7 @@ static char *solve_game(game_state *state, game_state *currstate,
                 continue;
            assert(!state->map->immutable[i]);
 
-            len = sprintf(buf, "%s%d:%d", retlen ? ";" : "S;",
-                         colouring[i], i);
+            len = sprintf(buf, ";%d:%d", colouring[i], i);
             if (retlen + len >= retsize) {
                 retsize = retlen + len + 256;
                 ret = sresize(ret, retsize, char);
@@ -1629,12 +1922,16 @@ static void game_changed_state(game_ui *ui, game_state *oldstate,
 
 struct game_drawstate {
     int tilesize;
-    unsigned char *drawn;
+    unsigned short *drawn, *todraw;
     int started;
     int dragx, dragy, drag_visible;
     blitter *bl;
 };
 
+/* Flags in `drawn'. */
+#define ERR_BASE 0x0080
+#define ERR_MASK 0xFF80
+
 #define TILESIZE (ds->tilesize)
 #define BORDER (TILESIZE)
 #define COORD(x)  ( (x) * TILESIZE + BORDER )
@@ -1703,7 +2000,7 @@ static char *interpret_move(game_state *state, game_ui *ui, game_drawstate *ds,
         if (state->colouring[r] == c)
             return "";                 /* don't _need_ to change this region */
 
-       sprintf(buf, "%c:%d", (c < 0 ? 'C' : '0' + c), r);
+       sprintf(buf, "%c:%d", (int)(c < 0 ? 'C' : '0' + c), r);
        return dupstr(buf);
     }
 
@@ -1784,16 +2081,26 @@ static void game_compute_size(game_params *params, int tilesize,
     *y = params->h * TILESIZE + 2 * BORDER + 1;
 }
 
-static void game_set_size(game_drawstate *ds, game_params *params,
-                         int tilesize)
+static void game_set_size(drawing *dr, game_drawstate *ds,
+                         game_params *params, int tilesize)
 {
     ds->tilesize = tilesize;
 
     if (ds->bl)
-        blitter_free(ds->bl);
-    ds->bl = blitter_new(TILESIZE+3, TILESIZE+3);
+        blitter_free(dr, ds->bl);
+    ds->bl = blitter_new(dr, TILESIZE+3, TILESIZE+3);
 }
 
+const float map_colours[FOUR][3] = {
+    {0.7F, 0.5F, 0.4F},
+    {0.8F, 0.7F, 0.4F},
+    {0.5F, 0.6F, 0.4F},
+    {0.55F, 0.45F, 0.35F},
+};
+const int map_hatching[FOUR] = {
+    HATCH_VERT, HATCH_SLASH, HATCH_HORIZ, HATCH_BACKSLASH
+};
+
 static float *game_colours(frontend *fe, game_state *state, int *ncolours)
 {
     float *ret = snewn(3 * NCOLOURS, float);
@@ -1804,33 +2111,33 @@ static float *game_colours(frontend *fe, game_state *state, int *ncolours)
     ret[COL_GRID * 3 + 1] = 0.0F;
     ret[COL_GRID * 3 + 2] = 0.0F;
 
-    ret[COL_0 * 3 + 0] = 0.7F;
-    ret[COL_0 * 3 + 1] = 0.5F;
-    ret[COL_0 * 3 + 2] = 0.4F;
-
-    ret[COL_1 * 3 + 0] = 0.8F;
-    ret[COL_1 * 3 + 1] = 0.7F;
-    ret[COL_1 * 3 + 2] = 0.4F;
+    memcpy(ret + COL_0 * 3, map_colours[0], 3 * sizeof(float));
+    memcpy(ret + COL_1 * 3, map_colours[1], 3 * sizeof(float));
+    memcpy(ret + COL_2 * 3, map_colours[2], 3 * sizeof(float));
+    memcpy(ret + COL_3 * 3, map_colours[3], 3 * sizeof(float));
 
-    ret[COL_2 * 3 + 0] = 0.5F;
-    ret[COL_2 * 3 + 1] = 0.6F;
-    ret[COL_2 * 3 + 2] = 0.4F;
+    ret[COL_ERROR * 3 + 0] = 1.0F;
+    ret[COL_ERROR * 3 + 1] = 0.0F;
+    ret[COL_ERROR * 3 + 2] = 0.0F;
 
-    ret[COL_3 * 3 + 0] = 0.55F;
-    ret[COL_3 * 3 + 1] = 0.45F;
-    ret[COL_3 * 3 + 2] = 0.35F;
+    ret[COL_ERRTEXT * 3 + 0] = 1.0F;
+    ret[COL_ERRTEXT * 3 + 1] = 1.0F;
+    ret[COL_ERRTEXT * 3 + 2] = 1.0F;
 
     *ncolours = NCOLOURS;
     return ret;
 }
 
-static game_drawstate *game_new_drawstate(game_state *state)
+static game_drawstate *game_new_drawstate(drawing *dr, game_state *state)
 {
     struct game_drawstate *ds = snew(struct game_drawstate);
+    int i;
 
     ds->tilesize = 0;
-    ds->drawn = snewn(state->p.w * state->p.h, unsigned char);
-    memset(ds->drawn, 0xFF, state->p.w * state->p.h);
+    ds->drawn = snewn(state->p.w * state->p.h, unsigned short);
+    for (i = 0; i < state->p.w * state->p.h; i++)
+       ds->drawn[i] = 0xFFFF;
+    ds->todraw = snewn(state->p.w * state->p.h, unsigned short);
     ds->started = FALSE;
     ds->bl = NULL;
     ds->drag_visible = FALSE;
@@ -1839,26 +2146,64 @@ static game_drawstate *game_new_drawstate(game_state *state)
     return ds;
 }
 
-static void game_free_drawstate(game_drawstate *ds)
+static void game_free_drawstate(drawing *dr, game_drawstate *ds)
 {
+    sfree(ds->drawn);
+    sfree(ds->todraw);
     if (ds->bl)
-        blitter_free(ds->bl);
+        blitter_free(dr, ds->bl);
     sfree(ds);
 }
 
-static void draw_square(frontend *fe, game_drawstate *ds,
+static void draw_error(drawing *dr, game_drawstate *ds, int x, int y)
+{
+    int coords[8];
+    int yext, xext;
+
+    /*
+     * Draw a diamond.
+     */
+    coords[0] = x - TILESIZE*2/5;
+    coords[1] = y;
+    coords[2] = x;
+    coords[3] = y - TILESIZE*2/5;
+    coords[4] = x + TILESIZE*2/5;
+    coords[5] = y;
+    coords[6] = x;
+    coords[7] = y + TILESIZE*2/5;
+    draw_polygon(dr, coords, 4, COL_ERROR, COL_GRID);
+
+    /*
+     * Draw an exclamation mark in the diamond. This turns out to
+     * look unpleasantly off-centre if done via draw_text, so I do
+     * it by hand on the basis that exclamation marks aren't that
+     * difficult to draw...
+     */
+    xext = TILESIZE/16;
+    yext = TILESIZE*2/5 - (xext*2+2);
+    draw_rect(dr, x-xext, y-yext, xext*2+1, yext*2+1 - (xext*3),
+             COL_ERRTEXT);
+    draw_rect(dr, x-xext, y+yext-xext*2+1, xext*2+1, xext*2, COL_ERRTEXT);
+}
+
+static void draw_square(drawing *dr, game_drawstate *ds,
                        game_params *params, struct map *map,
                        int x, int y, int v)
 {
     int w = params->w, h = params->h, wh = w*h;
-    int tv = v / FIVE, bv = v % FIVE;
+    int tv, bv, xo, yo, errs;
 
-    clip(fe, COORD(x), COORD(y), TILESIZE, TILESIZE);
+    errs = v & ERR_MASK;
+    v &= ~ERR_MASK;
+    tv = v / FIVE;
+    bv = v % FIVE;
+
+    clip(dr, COORD(x), COORD(y), TILESIZE, TILESIZE);
 
     /*
      * Draw the region colour.
      */
-    draw_rect(fe, COORD(x), COORD(y), TILESIZE, TILESIZE,
+    draw_rect(dr, COORD(x), COORD(y), TILESIZE, TILESIZE,
              (tv == FOUR ? COL_BACKGROUND : COL_0 + tv));
     /*
      * Draw the second region colour, if this is a diagonally
@@ -1875,7 +2220,7 @@ static void draw_square(frontend *fe, game_drawstate *ds,
         coords[3] = COORD(y)-1;
         coords[4] = COORD(x+1)+1;
         coords[5] = COORD(y+1)+1;
-        draw_polygon(fe, coords, 3,
+        draw_polygon(dr, coords, 3,
                      (bv == FOUR ? COL_BACKGROUND : COL_0 + bv), COL_GRID);
     }
 
@@ -1883,29 +2228,40 @@ static void draw_square(frontend *fe, game_drawstate *ds,
      * Draw the grid lines, if required.
      */
     if (x <= 0 || map->map[RE*wh+y*w+(x-1)] != map->map[LE*wh+y*w+x])
-       draw_rect(fe, COORD(x), COORD(y), 1, TILESIZE, COL_GRID);
+       draw_rect(dr, COORD(x), COORD(y), 1, TILESIZE, COL_GRID);
     if (y <= 0 || map->map[BE*wh+(y-1)*w+x] != map->map[TE*wh+y*w+x])
-       draw_rect(fe, COORD(x), COORD(y), TILESIZE, 1, COL_GRID);
+       draw_rect(dr, COORD(x), COORD(y), TILESIZE, 1, COL_GRID);
     if (x <= 0 || y <= 0 ||
         map->map[RE*wh+(y-1)*w+(x-1)] != map->map[TE*wh+y*w+x] ||
         map->map[BE*wh+(y-1)*w+(x-1)] != map->map[LE*wh+y*w+x])
-       draw_rect(fe, COORD(x), COORD(y), 1, 1, COL_GRID);
+       draw_rect(dr, COORD(x), COORD(y), 1, 1, COL_GRID);
+
+    /*
+     * Draw error markers.
+     */
+    for (yo = 0; yo < 3; yo++)
+       for (xo = 0; xo < 3; xo++)
+           if (errs & (ERR_BASE << (yo*3+xo)))
+               draw_error(dr, ds,
+                          (COORD(x)*2+TILESIZE*xo)/2,
+                          (COORD(y)*2+TILESIZE*yo)/2);
+
+    unclip(dr);
 
-    unclip(fe);
-    draw_update(fe, COORD(x), COORD(y), TILESIZE, TILESIZE);
+    draw_update(dr, COORD(x), COORD(y), TILESIZE, TILESIZE);
 }
 
-static void game_redraw(frontend *fe, game_drawstate *ds, game_state *oldstate,
+static void game_redraw(drawing *dr, game_drawstate *ds, game_state *oldstate,
                        game_state *state, int dir, game_ui *ui,
                        float animtime, float flashtime)
 {
-    int w = state->p.w, h = state->p.h, wh = w*h /*, n = state->p.n */;
-    int x, y;
+    int w = state->p.w, h = state->p.h, wh = w*h, n = state->p.n;
+    int x, y, i;
     int flash;
 
     if (ds->drag_visible) {
-        blitter_load(fe, ds->bl, ds->dragx, ds->dragy);
-        draw_update(fe, ds->dragx, ds->dragy, TILESIZE + 3, TILESIZE + 3);
+        blitter_load(dr, ds->bl, ds->dragx, ds->dragy);
+        draw_update(dr, ds->dragx, ds->dragy, TILESIZE + 3, TILESIZE + 3);
         ds->drag_visible = FALSE;
     }
 
@@ -1919,11 +2275,11 @@ static void game_redraw(frontend *fe, game_drawstate *ds, game_state *oldstate,
        int ww, wh;
 
        game_compute_size(&state->p, TILESIZE, &ww, &wh);
-       draw_rect(fe, 0, 0, ww, wh, COL_BACKGROUND);
-       draw_rect(fe, COORD(0), COORD(0), w*TILESIZE+1, h*TILESIZE+1,
+       draw_rect(dr, 0, 0, ww, wh, COL_BACKGROUND);
+       draw_rect(dr, COORD(0), COORD(0), w*TILESIZE+1, h*TILESIZE+1,
                  COL_GRID);
 
-       draw_update(fe, 0, 0, ww, wh);
+       draw_update(dr, 0, 0, ww, wh);
        ds->started = TRUE;
     }
 
@@ -1935,6 +2291,9 @@ static void game_redraw(frontend *fe, game_drawstate *ds, game_state *oldstate,
     } else
        flash = -1;
 
+    /*
+     * Set up the `todraw' array.
+     */
     for (y = 0; y < h; y++)
        for (x = 0; x < w; x++) {
            int tv = state->colouring[state->map->map[TE * wh + y*w+x]];
@@ -1965,8 +2324,51 @@ static void game_redraw(frontend *fe, game_drawstate *ds, game_state *oldstate,
 
             v = tv * FIVE + bv;
 
+           ds->todraw[y*w+x] = v;
+       }
+
+    /*
+     * Add error markers to the `todraw' array.
+     */
+    for (i = 0; i < state->map->ngraph; i++) {
+       int v1 = state->map->graph[i] / n;
+       int v2 = state->map->graph[i] % n;
+       int xo, yo;
+
+       if (state->colouring[v1] < 0 || state->colouring[v2] < 0)
+           continue;
+       if (state->colouring[v1] != state->colouring[v2])
+           continue;
+
+       x = state->map->edgex[i];
+       y = state->map->edgey[i];
+
+       xo = x % 2; x /= 2;
+       yo = y % 2; y /= 2;
+
+       ds->todraw[y*w+x] |= ERR_BASE << (yo*3+xo);
+       if (xo == 0) {
+           assert(x > 0);
+           ds->todraw[y*w+(x-1)] |= ERR_BASE << (yo*3+2);
+       }
+       if (yo == 0) {
+           assert(y > 0);
+           ds->todraw[(y-1)*w+x] |= ERR_BASE << (2*3+xo);
+       }
+       if (xo == 0 && yo == 0) {
+           assert(x > 0 && y > 0);
+           ds->todraw[(y-1)*w+(x-1)] |= ERR_BASE << (2*3+2);
+       }
+    }
+
+    /*
+     * Now actually draw everything.
+     */
+    for (y = 0; y < h; y++)
+       for (x = 0; x < w; x++) {
+           int v = ds->todraw[y*w+x];
            if (ds->drawn[y*w+x] != v) {
-               draw_square(fe, ds, &state->p, state->map, x, y, v);
+               draw_square(dr, ds, &state->p, state->map, x, y, v);
                ds->drawn[y*w+x] = v;
            }
        }
@@ -1977,11 +2379,11 @@ static void game_redraw(frontend *fe, game_drawstate *ds, game_state *oldstate,
     if (ui->drag_colour > -2) {
         ds->dragx = ui->dragx - TILESIZE/2 - 2;
         ds->dragy = ui->dragy - TILESIZE/2 - 2;
-        blitter_save(fe, ds->bl, ds->dragx, ds->dragy);
-        draw_circle(fe, ui->dragx, ui->dragy, TILESIZE/2,
+        blitter_save(dr, ds->bl, ds->dragx, ds->dragy);
+        draw_circle(dr, ui->dragx, ui->dragy, TILESIZE/2,
                     (ui->drag_colour < 0 ? COL_BACKGROUND :
                      COL_0 + ui->drag_colour), COL_GRID);
-        draw_update(fe, ds->dragx, ds->dragy, TILESIZE + 3, TILESIZE + 3);
+        draw_update(dr, ds->dragx, ds->dragy, TILESIZE + 3, TILESIZE + 3);
         ds->drag_visible = TRUE;
     }
 }
@@ -2020,6 +2422,157 @@ static int game_timing_state(game_state *state, game_ui *ui)
     return TRUE;
 }
 
+static void game_print_size(game_params *params, float *x, float *y)
+{
+    int pw, ph;
+
+    /*
+     * I'll use 4mm squares by default, I think. Simplest way to
+     * compute this size is to compute the pixel puzzle size at a
+     * given tile size and then scale.
+     */
+    game_compute_size(params, 400, &pw, &ph);
+    *x = pw / 100.0;
+    *y = ph / 100.0;
+}
+
+static void game_print(drawing *dr, game_state *state, int tilesize)
+{
+    int w = state->p.w, h = state->p.h, wh = w*h, n = state->p.n;
+    int ink, c[FOUR], i;
+    int x, y, r;
+    int *coords, ncoords, coordsize;
+
+    /* Ick: fake up `ds->tilesize' for macro expansion purposes */
+    struct { int tilesize; } ads, *ds = &ads;
+    ads.tilesize = tilesize;
+
+    ink = print_mono_colour(dr, 0);
+    for (i = 0; i < FOUR; i++)
+       c[i] = print_rgb_colour(dr, map_hatching[i], map_colours[i][0],
+                               map_colours[i][1], map_colours[i][2]);
+
+    coordsize = 0;
+    coords = NULL;
+
+    print_line_width(dr, TILESIZE / 16);
+
+    /*
+     * Draw a single filled polygon around each region.
+     */
+    for (r = 0; r < n; r++) {
+       int octants[8], lastdir, d1, d2, ox, oy;
+
+       /*
+        * Start by finding a point on the region boundary. Any
+        * point will do. To do this, we'll search for a square
+        * containing the region and then decide which corner of it
+        * to use.
+        */
+       x = w;
+       for (y = 0; y < h; y++) {
+           for (x = 0; x < w; x++) {
+               if (state->map->map[wh*0+y*w+x] == r ||
+                   state->map->map[wh*1+y*w+x] == r ||
+                   state->map->map[wh*2+y*w+x] == r ||
+                   state->map->map[wh*3+y*w+x] == r)
+                   break;
+           }
+           if (x < w)
+               break;
+       }
+       assert(y < h && x < w);        /* we must have found one somewhere */
+       /*
+        * This is the first square in lexicographic order which
+        * contains part of this region. Therefore, one of the top
+        * two corners of the square must be what we're after. The
+        * only case in which it isn't the top left one is if the
+        * square is diagonally divided and the region is in the
+        * bottom right half.
+        */
+       if (state->map->map[wh*TE+y*w+x] != r &&
+           state->map->map[wh*LE+y*w+x] != r)
+           x++;                       /* could just as well have done y++ */
+
+       /*
+        * Now we have a point on the region boundary. Trace around
+        * the region until we come back to this point,
+        * accumulating coordinates for a polygon draw operation as
+        * we go.
+        */
+       lastdir = -1;
+       ox = x;
+       oy = y;
+       ncoords = 0;
+
+       do {
+           /*
+            * There are eight possible directions we could head in
+            * from here. We identify them by octant numbers, and
+            * we also use octant numbers to identify the spaces
+            * between them:
+            * 
+            *   6   7   0
+            *    \ 7|0 /
+            *     \ | /
+            *    6 \|/ 1
+            * 5-----+-----1
+            *    5 /|\ 2
+            *     / | \
+            *    / 4|3 \
+            *   4   3   2
+            */
+           octants[0] = x<w && y>0 ? state->map->map[wh*LE+(y-1)*w+x] : -1;
+           octants[1] = x<w && y>0 ? state->map->map[wh*BE+(y-1)*w+x] : -1;
+           octants[2] = x<w && y<h ? state->map->map[wh*TE+y*w+x] : -1;
+           octants[3] = x<w && y<h ? state->map->map[wh*LE+y*w+x] : -1;
+           octants[4] = x>0 && y<h ? state->map->map[wh*RE+y*w+(x-1)] : -1;
+           octants[5] = x>0 && y<h ? state->map->map[wh*TE+y*w+(x-1)] : -1;
+           octants[6] = x>0 && y>0 ? state->map->map[wh*BE+(y-1)*w+(x-1)] :-1;
+           octants[7] = x>0 && y>0 ? state->map->map[wh*RE+(y-1)*w+(x-1)] :-1;
+
+           d1 = d2 = -1;
+           for (i = 0; i < 8; i++)
+               if ((octants[i] == r) ^ (octants[(i+1)%8] == r)) {
+                   assert(d2 == -1);
+                   if (d1 == -1)
+                       d1 = i;
+                   else
+                       d2 = i;
+               }
+/* printf("%% %d,%d r=%d: d1=%d d2=%d lastdir=%d\n", x, y, r, d1, d2, lastdir); */
+           assert(d1 != -1 && d2 != -1);
+           if (d1 == lastdir)
+               d1 = d2;
+
+           /*
+            * Now we're heading in direction d1. Save the current
+            * coordinates.
+            */
+           if (ncoords + 2 > coordsize) {
+               coordsize += 128;
+               coords = sresize(coords, coordsize, int);
+           }
+           coords[ncoords++] = COORD(x);
+           coords[ncoords++] = COORD(y);
+
+           /*
+            * Compute the new coordinates.
+            */
+           x += (d1 % 4 == 3 ? 0 : d1 < 4 ? +1 : -1);
+           y += (d1 % 4 == 1 ? 0 : d1 > 1 && d1 < 5 ? +1 : -1);
+           assert(x >= 0 && x <= w && y >= 0 && y <= h);
+
+           lastdir = d1 ^ 4;
+       } while (x != ox || y != oy);
+
+       draw_polygon(dr, coords, ncoords/2,
+                    state->colouring[r] >= 0 ?
+                    c[state->colouring[r]] : -1, ink);
+    }
+    sfree(coords);
+}
+
 #ifdef COMBINED
 #define thegame map
 #endif
@@ -2055,6 +2608,7 @@ const struct game thegame = {
     game_redraw,
     game_anim_length,
     game_flash_length,
+    TRUE, TRUE, game_print_size, game_print,
     game_wants_statusbar,
     FALSE, game_timing_state,
     0,                                /* mouse_priorities */