puzzles: refactor and resync with upstream

This brings puzzles up-to-date with upstream revision
2d333750272c3967cfd5cd3677572cddeaad5932, though certain changes made
by me, including cursor-only Untangle and some compilation fixes
remain. Upstream code has been moved to its separate subdirectory and
future syncs can be done by simply copying over the new sources.

Change-Id: Ia6506ca5f78c3627165ea6791d38db414ace0804

1 files changed, 1893 insertions, 0 deletions

diff --git a/apps/plugins/puzzles/src/netslide.c b/apps/plugins/puzzles/src/netslide.c
new file mode 100644
index 0000000000..c56e1abd6a
--- /dev/null
+++ b/apps/plugins/puzzles/src/netslide.c
@@ -0,0 +1,1893 @@
+/*
+ * netslide.c: cross between Net and Sixteen, courtesy of Richard
+ * Boulton.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+#include <ctype.h>
+#include <math.h>
+
+#include "puzzles.h"
+#include "tree234.h"
+
+#define MATMUL(xr,yr,m,x,y) do { \
+    float rx, ry, xx = (x), yy = (y), *mat = (m); \
+    rx = mat[0] * xx + mat[2] * yy; \
+    ry = mat[1] * xx + mat[3] * yy; \
+    (xr) = rx; (yr) = ry; \
+} while (0)
+
+/* Direction and other bitfields */
+#define R 0x01
+#define U 0x02
+#define L 0x04
+#define D 0x08
+#define FLASHING 0x10
+#define ACTIVE 0x20
+/* Corner flags go in the barriers array */
+#define RU 0x10
+#define UL 0x20
+#define LD 0x40
+#define DR 0x80
+
+/* Get tile at given coordinate */
+#define T(state, x, y) ( (y) * (state)->width + (x) )
+
+/* Rotations: Anticlockwise, Clockwise, Flip, general rotate */
+#define A(x) ( (((x) & 0x07) << 1) | (((x) & 0x08) >> 3) )
+#define C(x) ( (((x) & 0x0E) >> 1) | (((x) & 0x01) << 3) )
+#define F(x) ( (((x) & 0x0C) >> 2) | (((x) & 0x03) << 2) )
+#define ROT(x, n) ( ((n)&3) == 0 ? (x) : \
+                    ((n)&3) == 1 ? A(x) : \
+                    ((n)&3) == 2 ? F(x) : C(x) )
+
+/* X and Y displacements */
+#define X(x) ( (x) == R ? +1 : (x) == L ? -1 : 0 )
+#define Y(x) ( (x) == D ? +1 : (x) == U ? -1 : 0 )
+
+/* Bit count */
+#define COUNT(x) ( (((x) & 0x08) >> 3) + (((x) & 0x04) >> 2) + \
+                   (((x) & 0x02) >> 1) + ((x) & 0x01) )
+
+#define PREFERRED_TILE_SIZE 48
+#define TILE_SIZE (ds->tilesize)
+#define BORDER TILE_SIZE
+#define TILE_BORDER 1
+#define WINDOW_OFFSET 0
+
+#define ANIM_TIME 0.13F
+#define FLASH_FRAME 0.07F
+
+enum {
+    COL_BACKGROUND,
+    COL_FLASHING,
+    COL_BORDER,
+    COL_WIRE,
+    COL_ENDPOINT,
+    COL_POWERED,
+    COL_BARRIER,
+    COL_LOWLIGHT,
+    COL_TEXT,
+    NCOLOURS
+};
+
+struct game_params {
+    int width;
+    int height;
+    int wrapping;
+    float barrier_probability;
+    int movetarget;
+};
+
+struct game_state {
+    int width, height, cx, cy, wrapping, completed;
+    int used_solve;
+    int move_count, movetarget;
+
+    /* position (row or col number, starting at 0) of last move. */
+    int last_move_row, last_move_col;
+
+    /* direction of last move: +1 or -1 */
+    int last_move_dir;
+
+    unsigned char *tiles;
+    unsigned char *barriers;
+};
+
+#define OFFSET(x2,y2,x1,y1,dir,state) \
+    ( (x2) = ((x1) + (state)->width + X((dir))) % (state)->width, \
+      (y2) = ((y1) + (state)->height + Y((dir))) % (state)->height)
+
+#define index(state, a, x, y) ( a[(y) * (state)->width + (x)] )
+#define tile(state, x, y)     index(state, (state)->tiles, x, y)
+#define barrier(state, x, y)  index(state, (state)->barriers, x, y)
+
+struct xyd {
+    int x, y, direction;
+};
+
+static int xyd_cmp(void *av, void *bv) {
+    struct xyd *a = (struct xyd *)av;
+    struct xyd *b = (struct xyd *)bv;
+    if (a->x < b->x)
+        return -1;
+    if (a->x > b->x)
+        return +1;
+    if (a->y < b->y)
+        return -1;
+    if (a->y > b->y)
+        return +1;
+    if (a->direction < b->direction)
+        return -1;
+    if (a->direction > b->direction)
+        return +1;
+    return 0;
+}
+
+static struct xyd *new_xyd(int x, int y, int direction)
+{
+    struct xyd *xyd = snew(struct xyd);
+    xyd->x = x;
+    xyd->y = y;
+    xyd->direction = direction;
+    return xyd;
+}
+
+static void slide_col(game_state *state, int dir, int col);
+static void slide_col_int(int w, int h, unsigned char *tiles, int dir, int col);
+static void slide_row(game_state *state, int dir, int row);
+static void slide_row_int(int w, int h, unsigned char *tiles, int dir, int row);
+
+/* ----------------------------------------------------------------------
+ * Manage game parameters.
+ */
+static game_params *default_params(void)
+{
+    game_params *ret = snew(game_params);
+
+    ret->width = 3;
+    ret->height = 3;
+    ret->wrapping = FALSE;
+    ret->barrier_probability = 1.0;
+    ret->movetarget = 0;
+
+    return ret;
+}
+
+static const struct { int x, y, wrap, bprob; const char* desc; }
+netslide_presets[] = {
+    {3, 3, FALSE, 1, " easy"},
+    {3, 3, FALSE, 0, " medium"},
+    {3, 3, TRUE,  0, " hard"},
+    {4, 4, FALSE, 1, " easy"},
+    {4, 4, FALSE, 0, " medium"},
+    {4, 4, TRUE,  0, " hard"},
+    {5, 5, FALSE, 1, " easy"},
+    {5, 5, FALSE, 0, " medium"},
+    {5, 5, TRUE,  0, " hard"},
+};
+
+static int game_fetch_preset(int i, char **name, game_params **params)
+{
+    game_params *ret;
+    char str[80];
+
+    if (i < 0 || i >= lenof(netslide_presets))
+        return FALSE;
+
+    ret = snew(game_params);
+    ret->width = netslide_presets[i].x;
+    ret->height = netslide_presets[i].y;
+    ret->wrapping = netslide_presets[i].wrap;
+    ret->barrier_probability = (float)netslide_presets[i].bprob;
+    ret->movetarget = 0;
+
+    sprintf(str, "%dx%d%s", ret->width, ret->height, netslide_presets[i].desc);
+
+    *name = dupstr(str);
+    *params = ret;
+    return TRUE;
+}
+
+static void free_params(game_params *params)
+{
+    sfree(params);
+}
+
+static game_params *dup_params(const game_params *params)
+{
+    game_params *ret = snew(game_params);
+    *ret = *params;                    /* structure copy */
+    return ret;
+}
+
+static void decode_params(game_params *ret, char const *string)
+{
+    char const *p = string;
+
+    ret->wrapping = FALSE;
+    ret->barrier_probability = 0.0;
+    ret->movetarget = 0;
+
+    ret->width = atoi(p);
+    while (*p && isdigit((unsigned char)*p)) p++;
+    if (*p == 'x') {
+        p++;
+        ret->height = atoi(p);
+        while (*p && isdigit((unsigned char)*p)) p++;
+        if ( (ret->wrapping = (*p == 'w')) != 0 )
+            p++;
+        if (*p == 'b') {
+            ret->barrier_probability = (float)atof(++p);
+            while (*p && (isdigit((unsigned char)*p) || *p == '.')) p++;
+        }
+        if (*p == 'm') {
+            ret->movetarget = atoi(++p);
+        }
+    } else {
+        ret->height = ret->width;
+    }
+}
+
+static char *encode_params(const game_params *params, int full)
+{
+    char ret[400];
+    int len;
+
+    len = sprintf(ret, "%dx%d", params->width, params->height);
+    if (params->wrapping)
+        ret[len++] = 'w';
+    if (full && params->barrier_probability)
+        len += sprintf(ret+len, "b%g", params->barrier_probability);
+    /* Shuffle limit is part of the limited parameters, because we have to
+     * provide the target move count. */
+    if (params->movetarget)
+        len += sprintf(ret+len, "m%d", params->movetarget);
+    assert(len < lenof(ret));
+    ret[len] = '\0';
+
+    return dupstr(ret);
+}
+
+static config_item *game_configure(const game_params *params)
+{
+    config_item *ret;
+    char buf[80];
+
+    ret = snewn(6, config_item);
+
+    ret[0].name = "Width";
+    ret[0].type = C_STRING;
+    sprintf(buf, "%d", params->width);
+    ret[0].sval = dupstr(buf);
+    ret[0].ival = 0;
+
+    ret[1].name = "Height";
+    ret[1].type = C_STRING;
+    sprintf(buf, "%d", params->height);
+    ret[1].sval = dupstr(buf);
+    ret[1].ival = 0;
+
+    ret[2].name = "Walls wrap around";
+    ret[2].type = C_BOOLEAN;
+    ret[2].sval = NULL;
+    ret[2].ival = params->wrapping;
+
+    ret[3].name = "Barrier probability";
+    ret[3].type = C_STRING;
+    sprintf(buf, "%g", params->barrier_probability);
+    ret[3].sval = dupstr(buf);
+    ret[3].ival = 0;
+
+    ret[4].name = "Number of shuffling moves";
+    ret[4].type = C_STRING;
+    sprintf(buf, "%d", params->movetarget);
+    ret[4].sval = dupstr(buf);
+    ret[4].ival = 0;
+
+    ret[5].name = NULL;
+    ret[5].type = C_END;
+    ret[5].sval = NULL;
+    ret[5].ival = 0;
+
+    return ret;
+}
+
+static game_params *custom_params(const config_item *cfg)
+{
+    game_params *ret = snew(game_params);
+
+    ret->width = atoi(cfg[0].sval);
+    ret->height = atoi(cfg[1].sval);
+    ret->wrapping = cfg[2].ival;
+    ret->barrier_probability = (float)atof(cfg[3].sval);
+    ret->movetarget = atoi(cfg[4].sval);
+
+    return ret;
+}
+
+static char *validate_params(const game_params *params, int full)
+{
+    if (params->width <= 1 || params->height <= 1)
+        return "Width and height must both be greater than one";
+    if (params->barrier_probability < 0)
+        return "Barrier probability may not be negative";
+    if (params->barrier_probability > 1)
+        return "Barrier probability may not be greater than 1";
+    return NULL;
+}
+
+/* ----------------------------------------------------------------------
+ * Randomly select a new game description.
+ */
+
+static char *new_game_desc(const game_params *params, random_state *rs,
+                           char **aux, int interactive)
+{
+    tree234 *possibilities, *barriertree;
+    int w, h, x, y, cx, cy, nbarriers;
+    unsigned char *tiles, *barriers;
+    char *desc, *p;
+
+    w = params->width;
+    h = params->height;
+
+    tiles = snewn(w * h, unsigned char);
+    memset(tiles, 0, w * h);
+    barriers = snewn(w * h, unsigned char);
+    memset(barriers, 0, w * h);
+
+    cx = w / 2;
+    cy = h / 2;
+
+    /*
+     * Construct the unshuffled grid.
+     * 
+     * To do this, we simply start at the centre point, repeatedly
+     * choose a random possibility out of the available ways to
+     * extend a used square into an unused one, and do it. After
+     * extending the third line out of a square, we remove the
+     * fourth from the possibilities list to avoid any full-cross
+     * squares (which would make the game too easy because they
+     * only have one orientation).
+     * 
+     * The slightly worrying thing is the avoidance of full-cross
+     * squares. Can this cause our unsophisticated construction
+     * algorithm to paint itself into a corner, by getting into a
+     * situation where there are some unreached squares and the
+     * only way to reach any of them is to extend a T-piece into a
+     * full cross?
+     * 
+     * Answer: no it can't, and here's a proof.
+     * 
+     * Any contiguous group of such unreachable squares must be
+     * surrounded on _all_ sides by T-pieces pointing away from the
+     * group. (If not, then there is a square which can be extended
+     * into one of the `unreachable' ones, and so it wasn't
+     * unreachable after all.) In particular, this implies that
+     * each contiguous group of unreachable squares must be
+     * rectangular in shape (any deviation from that yields a
+     * non-T-piece next to an `unreachable' square).
+     * 
+     * So we have a rectangle of unreachable squares, with T-pieces
+     * forming a solid border around the rectangle. The corners of
+     * that border must be connected (since every tile connects all
+     * the lines arriving in it), and therefore the border must
+     * form a closed loop around the rectangle.
+     * 
+     * But this can't have happened in the first place, since we
+     * _know_ we've avoided creating closed loops! Hence, no such
+     * situation can ever arise, and the naive grid construction
+     * algorithm will guaranteeably result in a complete grid
+     * containing no unreached squares, no full crosses _and_ no
+     * closed loops. []
+     */
+    possibilities = newtree234(xyd_cmp);
+
+    if (cx+1 < w)
+        add234(possibilities, new_xyd(cx, cy, R));
+    if (cy-1 >= 0)
+        add234(possibilities, new_xyd(cx, cy, U));
+    if (cx-1 >= 0)
+        add234(possibilities, new_xyd(cx, cy, L));
+    if (cy+1 < h)
+        add234(possibilities, new_xyd(cx, cy, D));
+
+    while (count234(possibilities) > 0) {
+        int i;
+        struct xyd *xyd;
+        int x1, y1, d1, x2, y2, d2, d;
+
+        /*
+         * Extract a randomly chosen possibility from the list.
+         */
+        i = random_upto(rs, count234(possibilities));
+        xyd = delpos234(possibilities, i);
+        x1 = xyd->x;
+        y1 = xyd->y;
+        d1 = xyd->direction;
+        sfree(xyd);
+
+        OFFSET(x2, y2, x1, y1, d1, params);
+        d2 = F(d1);
+#ifdef GENERATION_DIAGNOSTICS
+        printf("picked (%d,%d,%c) <-> (%d,%d,%c)\n",
+               x1, y1, "0RU3L567D9abcdef"[d1], x2, y2, "0RU3L567D9abcdef"[d2]);
+#endif
+
+        /*
+         * Make the connection. (We should be moving to an as yet
+         * unused tile.)
+         */
+        index(params, tiles, x1, y1) |= d1;
+        assert(index(params, tiles, x2, y2) == 0);
+        index(params, tiles, x2, y2) |= d2;
+
+        /*
+         * If we have created a T-piece, remove its last
+         * possibility.
+         */
+        if (COUNT(index(params, tiles, x1, y1)) == 3) {
+            struct xyd xyd1, *xydp;
+
+            xyd1.x = x1;
+            xyd1.y = y1;
+            xyd1.direction = 0x0F ^ index(params, tiles, x1, y1);
+
+            xydp = find234(possibilities, &xyd1, NULL);
+
+            if (xydp) {
+#ifdef GENERATION_DIAGNOSTICS
+                printf("T-piece; removing (%d,%d,%c)\n",
+                       xydp->x, xydp->y, "0RU3L567D9abcdef"[xydp->direction]);
+#endif
+                del234(possibilities, xydp);
+                sfree(xydp);
+            }
+        }
+
+        /*
+         * Remove all other possibilities that were pointing at the
+         * tile we've just moved into.
+         */
+        for (d = 1; d < 0x10; d <<= 1) {
+            int x3, y3, d3;
+            struct xyd xyd1, *xydp;
+
+            OFFSET(x3, y3, x2, y2, d, params);
+            d3 = F(d);
+
+            xyd1.x = x3;
+            xyd1.y = y3;
+            xyd1.direction = d3;
+
+            xydp = find234(possibilities, &xyd1, NULL);
+
+            if (xydp) {
+#ifdef GENERATION_DIAGNOSTICS
+                printf("Loop avoidance; removing (%d,%d,%c)\n",
+                       xydp->x, xydp->y, "0RU3L567D9abcdef"[xydp->direction]);
+#endif
+                del234(possibilities, xydp);
+                sfree(xydp);
+            }
+        }
+
+        /*
+         * Add new possibilities to the list for moving _out_ of
+         * the tile we have just moved into.
+         */
+        for (d = 1; d < 0x10; d <<= 1) {
+            int x3, y3;
+
+            if (d == d2)
+                continue;              /* we've got this one already */
+
+            if (!params->wrapping) {
+                if (d == U && y2 == 0)
+                    continue;
+                if (d == D && y2 == h-1)
+                    continue;
+                if (d == L && x2 == 0)
+                    continue;
+                if (d == R && x2 == w-1)
+                    continue;
+            }
+
+            OFFSET(x3, y3, x2, y2, d, params);
+
+            if (index(params, tiles, x3, y3))
+                continue;              /* this would create a loop */
+
+#ifdef GENERATION_DIAGNOSTICS
+            printf("New frontier; adding (%d,%d,%c)\n",
+                   x2, y2, "0RU3L567D9abcdef"[d]);
+#endif
+            add234(possibilities, new_xyd(x2, y2, d));
+        }
+    }
+    /* Having done that, we should have no possibilities remaining. */
+    assert(count234(possibilities) == 0);
+    freetree234(possibilities);
+
+    /*
+     * Now compute a list of the possible barrier locations.
+     */
+    barriertree = newtree234(xyd_cmp);
+    for (y = 0; y < h; y++) {
+        for (x = 0; x < w; x++) {
+
+            if (!(index(params, tiles, x, y) & R) &&
+                (params->wrapping || x < w-1))
+                add234(barriertree, new_xyd(x, y, R));
+            if (!(index(params, tiles, x, y) & D) &&
+                (params->wrapping || y < h-1))
+                add234(barriertree, new_xyd(x, y, D));
+        }
+    }
+
+    /*
+     * Save the unshuffled grid in aux.
+     */
+    {
+        char *solution;
+        int i;
+
+        /*
+         * String format is exactly the same as a solve move, so we
+         * can just dupstr this in solve_game().
+         */
+
+        solution = snewn(w * h + 2, char);
+        solution[0] = 'S';
+        for (i = 0; i < w * h; i++)
+            solution[i+1] = "0123456789abcdef"[tiles[i] & 0xF];
+        solution[w*h+1] = '\0';
+
+        *aux = solution;
+    }
+
+    /*
+     * Now shuffle the grid.
+     * FIXME - this simply does a set of random moves to shuffle the pieces,
+     * although we make a token effort to avoid boring cases by avoiding moves
+     * that directly undo the previous one, or that repeat so often as to
+     * turn into fewer moves.
+     *
+     * A better way would be to number all the pieces, generate a placement
+     * for all the numbers as for "sixteen", observing parity constraints if
+     * neccessary, and then place the pieces according to their numbering.
+     * BUT - I'm not sure if this will work, since we disallow movement of
+     * the middle row and column.
+     */
+    {
+        int i;
+        int cols = w - 1;
+        int rows = h - 1;
+        int moves = params->movetarget;
+        int prevdir = -1, prevrowcol = -1, nrepeats = 0;
+        if (!moves) moves = cols * rows * 2;
+        for (i = 0; i < moves; /* incremented conditionally */) {
+            /* Choose a direction: 0,1,2,3 = up, right, down, left. */
+            int dir = random_upto(rs, 4);
+            int rowcol;
+            if (dir % 2 == 0) {
+                int col = random_upto(rs, cols);
+                if (col >= cx) col += 1;    /* avoid centre */
+                if (col == prevrowcol) {
+                    if (dir == 2-prevdir)
+                        continue;   /* undoes last move */
+                    else if (dir == prevdir && (nrepeats+1)*2 > h)
+                        continue;   /* makes fewer moves */
+                }
+                slide_col_int(w, h, tiles, 1 - dir, col);
+                rowcol = col;
+            } else {
+                int row = random_upto(rs, rows);
+                if (row >= cy) row += 1;    /* avoid centre */
+                if (row == prevrowcol) {
+                    if (dir == 4-prevdir)
+                        continue;   /* undoes last move */
+                    else if (dir == prevdir && (nrepeats+1)*2 > w)
+                        continue;   /* makes fewer moves */
+                }
+                slide_row_int(w, h, tiles, 2 - dir, row);
+                rowcol = row;
+            }
+            if (dir == prevdir && rowcol == prevrowcol)
+                nrepeats++;
+            else
+                nrepeats = 1;
+            prevdir = dir;
+            prevrowcol = rowcol;
+            i++;    /* if we got here, the move was accepted */
+        }
+    }
+
+    /*
+     * And now choose barrier locations. (We carefully do this
+     * _after_ shuffling, so that changing the barrier rate in the
+     * params while keeping the random seed the same will give the
+     * same shuffled grid and _only_ change the barrier locations.
+     * Also the way we choose barrier locations, by repeatedly
+     * choosing one possibility from the list until we have enough,
+     * is designed to ensure that raising the barrier rate while
+     * keeping the seed the same will provide a superset of the
+     * previous barrier set - i.e. if you ask for 10 barriers, and
+     * then decide that's still too hard and ask for 20, you'll get
+     * the original 10 plus 10 more, rather than getting 20 new
+     * ones and the chance of remembering your first 10.)
+     */
+    nbarriers = (int)(params->barrier_probability * count234(barriertree));
+    assert(nbarriers >= 0 && nbarriers <= count234(barriertree));
+
+    while (nbarriers > 0) {
+        int i;
+        struct xyd *xyd;
+        int x1, y1, d1, x2, y2, d2;
+
+        /*
+         * Extract a randomly chosen barrier from the list.
+         */
+        i = random_upto(rs, count234(barriertree));
+        xyd = delpos234(barriertree, i);
+
+        assert(xyd != NULL);
+
+        x1 = xyd->x;
+        y1 = xyd->y;
+        d1 = xyd->direction;
+        sfree(xyd);
+
+        OFFSET(x2, y2, x1, y1, d1, params);
+        d2 = F(d1);
+
+        index(params, barriers, x1, y1) |= d1;
+        index(params, barriers, x2, y2) |= d2;
+
+        nbarriers--;
+    }
+
+    /*
+     * Clean up the rest of the barrier list.
+     */
+    {
+        struct xyd *xyd;
+
+        while ( (xyd = delpos234(barriertree, 0)) != NULL)
+            sfree(xyd);
+
+        freetree234(barriertree);
+    }
+
+    /*
+     * Finally, encode the grid into a string game description.
+     * 
+     * My syntax is extremely simple: each square is encoded as a
+     * hex digit in which bit 0 means a connection on the right,
+     * bit 1 means up, bit 2 left and bit 3 down. (i.e. the same
+     * encoding as used internally). Each digit is followed by
+     * optional barrier indicators: `v' means a vertical barrier to
+     * the right of it, and `h' means a horizontal barrier below
+     * it.
+     */
+    desc = snewn(w * h * 3 + 1, char);
+    p = desc;
+    for (y = 0; y < h; y++) {
+        for (x = 0; x < w; x++) {
+            *p++ = "0123456789abcdef"[index(params, tiles, x, y)];
+            if ((params->wrapping || x < w-1) &&
+                (index(params, barriers, x, y) & R))
+                *p++ = 'v';
+            if ((params->wrapping || y < h-1) &&
+                (index(params, barriers, x, y) & D))
+                *p++ = 'h';
+        }
+    }
+    assert(p - desc <= w*h*3);
+    *p = '\0';
+
+    sfree(tiles);
+    sfree(barriers);
+
+    return desc;
+}
+
+static char *validate_desc(const game_params *params, const char *desc)
+{
+    int w = params->width, h = params->height;
+    int i;
+
+    for (i = 0; i < w*h; i++) {
+        if (*desc >= '0' && *desc <= '9')
+            /* OK */;
+        else if (*desc >= 'a' && *desc <= 'f')
+            /* OK */;
+        else if (*desc >= 'A' && *desc <= 'F')
+            /* OK */;
+        else if (!*desc)
+            return "Game description shorter than expected";
+        else
+            return "Game description contained unexpected character";
+        desc++;
+        while (*desc == 'h' || *desc == 'v')
+            desc++;
+    }
+    if (*desc)
+        return "Game description longer than expected";
+
+    return NULL;
+}
+
+/* ----------------------------------------------------------------------
+ * Construct an initial game state, given a description and parameters.
+ */
+
+static game_state *new_game(midend *me, const game_params *params,
+                            const char *desc)
+{
+    game_state *state;
+    int w, h, x, y;
+
+    assert(params->width > 0 && params->height > 0);
+    assert(params->width > 1 || params->height > 1);
+
+    /*
+     * Create a blank game state.
+     */
+    state = snew(game_state);
+    w = state->width = params->width;
+    h = state->height = params->height;
+    state->cx = state->width / 2;
+    state->cy = state->height / 2;
+    state->wrapping = params->wrapping;
+    state->movetarget = params->movetarget;
+    state->completed = 0;
+    state->used_solve = FALSE;
+    state->move_count = 0;
+    state->last_move_row = -1;
+    state->last_move_col = -1;
+    state->last_move_dir = 0;
+    state->tiles = snewn(state->width * state->height, unsigned char);
+    memset(state->tiles, 0, state->width * state->height);
+    state->barriers = snewn(state->width * state->height, unsigned char);
+    memset(state->barriers, 0, state->width * state->height);
+
+
+    /*
+     * Parse the game description into the grid.
+     */
+    for (y = 0; y < h; y++) {
+        for (x = 0; x < w; x++) {
+            if (*desc >= '0' && *desc <= '9')
+                tile(state, x, y) = *desc - '0';
+            else if (*desc >= 'a' && *desc <= 'f')
+                tile(state, x, y) = *desc - 'a' + 10;
+            else if (*desc >= 'A' && *desc <= 'F')
+                tile(state, x, y) = *desc - 'A' + 10;
+            if (*desc)
+                desc++;
+            while (*desc == 'h' || *desc == 'v') {
+                int x2, y2, d1, d2;
+                if (*desc == 'v')
+                    d1 = R;
+                else
+                    d1 = D;
+
+                OFFSET(x2, y2, x, y, d1, state);
+                d2 = F(d1);
+
+                barrier(state, x, y) |= d1;
+                barrier(state, x2, y2) |= d2;
+
+                desc++;
+            }
+        }
+    }
+
+    /*
+     * Set up border barriers if this is a non-wrapping game.
+     */
+    if (!state->wrapping) {
+        for (x = 0; x < state->width; x++) {
+            barrier(state, x, 0) |= U;
+            barrier(state, x, state->height-1) |= D;
+        }
+        for (y = 0; y < state->height; y++) {
+            barrier(state, 0, y) |= L;
+            barrier(state, state->width-1, y) |= R;
+        }
+    }
+
+    /*
+     * Set up the barrier corner flags, for drawing barriers
+     * prettily when they meet.
+     */
+    for (y = 0; y < state->height; y++) {
+        for (x = 0; x < state->width; x++) {
+            int dir;
+
+            for (dir = 1; dir < 0x10; dir <<= 1) {
+                int dir2 = A(dir);
+                int x1, y1, x2, y2, x3, y3;
+                int corner = FALSE;
+
+                if (!(barrier(state, x, y) & dir))
+                    continue;
+
+                if (barrier(state, x, y) & dir2)
+                    corner = TRUE;
+
+                x1 = x + X(dir), y1 = y + Y(dir);
+                if (x1 >= 0 && x1 < state->width &&
+                    y1 >= 0 && y1 < state->height &&
+                    (barrier(state, x1, y1) & dir2))
+                    corner = TRUE;
+
+                x2 = x + X(dir2), y2 = y + Y(dir2);
+                if (x2 >= 0 && x2 < state->width &&
+                    y2 >= 0 && y2 < state->height &&
+                    (barrier(state, x2, y2) & dir))
+                    corner = TRUE;
+
+                if (corner) {
+                    barrier(state, x, y) |= (dir << 4);
+                    if (x1 >= 0 && x1 < state->width &&
+                        y1 >= 0 && y1 < state->height)
+                        barrier(state, x1, y1) |= (A(dir) << 4);
+                    if (x2 >= 0 && x2 < state->width &&
+                        y2 >= 0 && y2 < state->height)
+                        barrier(state, x2, y2) |= (C(dir) << 4);
+                    x3 = x + X(dir) + X(dir2), y3 = y + Y(dir) + Y(dir2);
+                    if (x3 >= 0 && x3 < state->width &&
+                        y3 >= 0 && y3 < state->height)
+                        barrier(state, x3, y3) |= (F(dir) << 4);
+                }
+            }
+        }
+    }
+
+    return state;
+}
+
+static game_state *dup_game(const game_state *state)
+{
+    game_state *ret;
+
+    ret = snew(game_state);
+    ret->width = state->width;
+    ret->height = state->height;
+    ret->cx = state->cx;
+    ret->cy = state->cy;
+    ret->wrapping = state->wrapping;
+    ret->movetarget = state->movetarget;
+    ret->completed = state->completed;
+    ret->used_solve = state->used_solve;
+    ret->move_count = state->move_count;
+    ret->last_move_row = state->last_move_row;
+    ret->last_move_col = state->last_move_col;
+    ret->last_move_dir = state->last_move_dir;
+    ret->tiles = snewn(state->width * state->height, unsigned char);
+    memcpy(ret->tiles, state->tiles, state->width * state->height);
+    ret->barriers = snewn(state->width * state->height, unsigned char);
+    memcpy(ret->barriers, state->barriers, state->width * state->height);
+
+    return ret;
+}
+
+static void free_game(game_state *state)
+{
+    sfree(state->tiles);
+    sfree(state->barriers);
+    sfree(state);
+}
+
+static char *solve_game(const game_state *state, const game_state *currstate,
+                        const char *aux, char **error)
+{
+    if (!aux) {
+        *error = "Solution not known for this puzzle";
+        return NULL;
+    }
+
+    return dupstr(aux);
+}
+
+static int game_can_format_as_text_now(const game_params *params)
+{
+    return TRUE;
+}
+
+static char *game_text_format(const game_state *state)
+{
+    return NULL;
+}
+
+/* ----------------------------------------------------------------------
+ * Utility routine.
+ */
+
+/*
+ * Compute which squares are reachable from the centre square, as a
+ * quick visual aid to determining how close the game is to
+ * completion. This is also a simple way to tell if the game _is_
+ * completed - just call this function and see whether every square
+ * is marked active.
+ *
+ * squares in the moving_row and moving_col are always inactive - this
+ * is so that "current" doesn't appear to jump across moving lines.
+ */
+static unsigned char *compute_active(const game_state *state,
+                                     int moving_row, int moving_col)
+{
+    unsigned char *active;
+    tree234 *todo;
+    struct xyd *xyd;
+
+    active = snewn(state->width * state->height, unsigned char);
+    memset(active, 0, state->width * state->height);
+
+    /*
+     * We only store (x,y) pairs in todo, but it's easier to reuse
+     * xyd_cmp and just store direction 0 every time.
+     */
+    todo = newtree234(xyd_cmp);
+    index(state, active, state->cx, state->cy) = ACTIVE;
+    add234(todo, new_xyd(state->cx, state->cy, 0));
+
+    while ( (xyd = delpos234(todo, 0)) != NULL) {
+        int x1, y1, d1, x2, y2, d2;
+
+        x1 = xyd->x;
+        y1 = xyd->y;
+        sfree(xyd);
+
+        for (d1 = 1; d1 < 0x10; d1 <<= 1) {
+            OFFSET(x2, y2, x1, y1, d1, state);
+            d2 = F(d1);
+
+            /*
+             * If the next tile in this direction is connected to
+             * us, and there isn't a barrier in the way, and it
+             * isn't already marked active, then mark it active and
+             * add it to the to-examine list.
+             */
+            if ((x2 != moving_col && y2 != moving_row) &&
+                (tile(state, x1, y1) & d1) &&
+                (tile(state, x2, y2) & d2) &&
+                !(barrier(state, x1, y1) & d1) &&
+                !index(state, active, x2, y2)) {
+                index(state, active, x2, y2) = ACTIVE;
+                add234(todo, new_xyd(x2, y2, 0));
+            }
+        }
+    }
+    /* Now we expect the todo list to have shrunk to zero size. */
+    assert(count234(todo) == 0);
+    freetree234(todo);
+
+    return active;
+}
+
+struct game_ui {
+    int cur_x, cur_y;
+    int cur_visible;
+};
+
+static game_ui *new_ui(const game_state *state)
+{
+    game_ui *ui = snew(game_ui);
+    ui->cur_x = 0;
+    ui->cur_y = -1;
+    ui->cur_visible = FALSE;
+
+    return ui;
+}
+
+static void free_ui(game_ui *ui)
+{
+    sfree(ui);
+}
+
+static char *encode_ui(const game_ui *ui)
+{
+    return NULL;
+}
+
+static void decode_ui(game_ui *ui, const char *encoding)
+{
+}
+
+/* ----------------------------------------------------------------------
+ * Process a move.
+ */
+
+static void slide_row_int(int w, int h, unsigned char *tiles, int dir, int row)
+{
+    int x = dir > 0 ? -1 : w;
+    int tx = x + dir;
+    int n = w - 1;
+    unsigned char endtile = tiles[row * w + tx];
+    do {
+        x = tx;
+        tx = (x + dir + w) % w;
+        tiles[row * w + x] = tiles[row * w + tx];
+    } while (--n > 0);
+    tiles[row * w + tx] = endtile;
+}
+
+static void slide_col_int(int w, int h, unsigned char *tiles, int dir, int col)
+{
+    int y = dir > 0 ? -1 : h;
+    int ty = y + dir;
+    int n = h - 1;
+    unsigned char endtile = tiles[ty * w + col];
+    do {
+        y = ty;
+        ty = (y + dir + h) % h;
+        tiles[y * w + col] = tiles[ty * w + col];
+    } while (--n > 0);
+    tiles[ty * w + col] = endtile;
+}
+
+static void slide_row(game_state *state, int dir, int row)
+{
+    slide_row_int(state->width, state->height, state->tiles, dir, row);
+}
+
+static void slide_col(game_state *state, int dir, int col)
+{
+    slide_col_int(state->width, state->height, state->tiles, dir, col);
+}
+
+static void game_changed_state(game_ui *ui, const game_state *oldstate,
+                               const game_state *newstate)
+{
+}
+
+struct game_drawstate {
+    int started;
+    int width, height;
+    int tilesize;
+    unsigned char *visible;
+    int cur_x, cur_y;
+};
+
+static char *interpret_move(const game_state *state, game_ui *ui,
+                            const game_drawstate *ds,
+                            int x, int y, int button)
+{
+    int cx, cy;
+    int dx, dy;
+    char buf[80];
+
+    button &= ~MOD_MASK;
+
+    if (IS_CURSOR_MOVE(button)) {
+        int cpos, diff = 0;
+        cpos = c2pos(state->width, state->height, ui->cur_x, ui->cur_y);
+        diff = c2diff(state->width, state->height, ui->cur_x, ui->cur_y, button);
+
+        if (diff != 0) {
+            do { /* we might have to do this more than once to skip missing arrows */
+                cpos += diff;
+                pos2c(state->width, state->height, cpos, &ui->cur_x, &ui->cur_y);
+            } while (ui->cur_x == state->cx || ui->cur_y == state->cy);
+        }
+
+        ui->cur_visible = 1;
+        return "";
+    }
+
+    if (button == LEFT_BUTTON || button == RIGHT_BUTTON) {
+        cx = (x - (BORDER + WINDOW_OFFSET + TILE_BORDER) + 2*TILE_SIZE) / TILE_SIZE - 2;
+        cy = (y - (BORDER + WINDOW_OFFSET + TILE_BORDER) + 2*TILE_SIZE) / TILE_SIZE - 2;
+        ui->cur_visible = 0;
+    } else if (IS_CURSOR_SELECT(button)) {
+        if (ui->cur_visible) {
+            cx = ui->cur_x;
+            cy = ui->cur_y;
+        } else {
+            /* 'click' when cursor is invisible just makes cursor visible. */
+            ui->cur_visible = 1;
+            return "";
+        }
+    } else
+        return NULL;
+
+    if (cy >= 0 && cy < state->height && cy != state->cy)
+    {
+        if (cx == -1) dx = +1;
+        else if (cx == state->width) dx = -1;
+        else return NULL;
+        dy = 0;
+    }
+    else if (cx >= 0 && cx < state->width && cx != state->cx)
+    {
+        if (cy == -1) dy = +1;
+        else if (cy == state->height) dy = -1;
+        else return NULL;
+        dx = 0;
+    }
+    else
+        return NULL;
+
+    /* reverse direction if right hand button is pressed */
+    if (button == RIGHT_BUTTON)
+    {
+        dx = -dx;
+        dy = -dy;
+    }
+
+    if (dx == 0)
+        sprintf(buf, "C%d,%d", cx, dy);
+    else
+        sprintf(buf, "R%d,%d", cy, dx);
+    return dupstr(buf);
+}
+
+static game_state *execute_move(const game_state *from, const char *move)
+{
+    game_state *ret;
+    int c, d, col;
+
+    if ((move[0] == 'C' || move[0] == 'R') &&
+        sscanf(move+1, "%d,%d", &c, &d) == 2 &&
+        c >= 0 && c < (move[0] == 'C' ? from->width : from->height)) {
+        col = (move[0] == 'C');
+    } else if (move[0] == 'S' &&
+               strlen(move) == from->width * from->height + 1) {
+        int i;
+        ret = dup_game(from);
+        ret->used_solve = TRUE;
+        ret->completed = ret->move_count = 1;
+
+        for (i = 0; i < from->width * from->height; i++) {
+            c = move[i+1];
+            if (c >= '0' && c <= '9')
+                c -= '0';
+            else if (c >= 'A' && c <= 'F')
+                c -= 'A' - 10;
+            else if (c >= 'a' && c <= 'f')
+                c -= 'a' - 10;
+            else {
+                free_game(ret);
+                return NULL;
+            }
+            ret->tiles[i] = c;
+        }
+        return ret;
+    } else
+        return NULL;                   /* can't parse move string */
+
+    ret = dup_game(from);
+
+    if (col)
+        slide_col(ret, d, c);
+    else
+        slide_row(ret, d, c);
+
+    ret->move_count++;
+    ret->last_move_row = col ? -1 : c;
+    ret->last_move_col = col ? c : -1;
+    ret->last_move_dir = d;
+
+    /*
+     * See if the game has been completed.
+     */
+    if (!ret->completed) {
+        unsigned char *active = compute_active(ret, -1, -1);
+        int x1, y1;
+        int complete = TRUE;
+
+        for (x1 = 0; x1 < ret->width; x1++)
+            for (y1 = 0; y1 < ret->height; y1++)
+                if (!index(ret, active, x1, y1)) {
+                    complete = FALSE;
+                    goto break_label;  /* break out of two loops at once */
+                }
+        break_label:
+
+        sfree(active);
+
+        if (complete)
+            ret->completed = ret->move_count;
+    }
+
+    return ret;
+}
+
+/* ----------------------------------------------------------------------
+ * Routines for drawing the game position on the screen.
+ */
+
+static game_drawstate *game_new_drawstate(drawing *dr, const game_state *state)
+{
+    game_drawstate *ds = snew(game_drawstate);
+
+    ds->started = FALSE;
+    ds->width = state->width;
+    ds->height = state->height;
+    ds->visible = snewn(state->width * state->height, unsigned char);
+    ds->tilesize = 0;                  /* not decided yet */
+    memset(ds->visible, 0xFF, state->width * state->height);
+    ds->cur_x = ds->cur_y = -1;
+
+    return ds;
+}
+
+static void game_free_drawstate(drawing *dr, game_drawstate *ds)
+{
+    sfree(ds->visible);
+    sfree(ds);
+}
+
+static void game_compute_size(const game_params *params, int tilesize,
+                              int *x, int *y)
+{
+    /* Ick: fake up `ds->tilesize' for macro expansion purposes */
+    struct { int tilesize; } ads, *ds = &ads;
+    ads.tilesize = tilesize;
+
+    *x = BORDER * 2 + WINDOW_OFFSET * 2 + TILE_SIZE * params->width + TILE_BORDER;
+    *y = BORDER * 2 + WINDOW_OFFSET * 2 + TILE_SIZE * params->height + TILE_BORDER;
+}
+
+static void game_set_size(drawing *dr, game_drawstate *ds,
+                          const game_params *params, int tilesize)
+{
+    ds->tilesize = tilesize;
+}
+
+static float *game_colours(frontend *fe, int *ncolours)
+{
+    float *ret;
+
+    ret = snewn(NCOLOURS * 3, float);
+    *ncolours = NCOLOURS;
+
+    /*
+     * Basic background colour is whatever the front end thinks is
+     * a sensible default.
+     */
+    frontend_default_colour(fe, &ret[COL_BACKGROUND * 3]);
+
+    /*
+     * Wires are black.
+     */
+    ret[COL_WIRE * 3 + 0] = 0.0F;
+    ret[COL_WIRE * 3 + 1] = 0.0F;
+    ret[COL_WIRE * 3 + 2] = 0.0F;
+
+    /*
+     * Powered wires and powered endpoints are cyan.
+     */
+    ret[COL_POWERED * 3 + 0] = 0.0F;
+    ret[COL_POWERED * 3 + 1] = 1.0F;
+    ret[COL_POWERED * 3 + 2] = 1.0F;
+
+    /*
+     * Barriers are red.
+     */
+    ret[COL_BARRIER * 3 + 0] = 1.0F;
+    ret[COL_BARRIER * 3 + 1] = 0.0F;
+    ret[COL_BARRIER * 3 + 2] = 0.0F;
+
+    /*
+     * Unpowered endpoints are blue.
+     */
+    ret[COL_ENDPOINT * 3 + 0] = 0.0F;
+    ret[COL_ENDPOINT * 3 + 1] = 0.0F;
+    ret[COL_ENDPOINT * 3 + 2] = 1.0F;
+
+    /*
+     * Tile borders are a darker grey than the background.
+     */
+    ret[COL_BORDER * 3 + 0] = 0.5F * ret[COL_BACKGROUND * 3 + 0];
+    ret[COL_BORDER * 3 + 1] = 0.5F * ret[COL_BACKGROUND * 3 + 1];
+    ret[COL_BORDER * 3 + 2] = 0.5F * ret[COL_BACKGROUND * 3 + 2];
+
+    /*
+     * Flashing tiles are a grey in between those two.
+     */
+    ret[COL_FLASHING * 3 + 0] = 0.75F * ret[COL_BACKGROUND * 3 + 0];
+    ret[COL_FLASHING * 3 + 1] = 0.75F * ret[COL_BACKGROUND * 3 + 1];
+    ret[COL_FLASHING * 3 + 2] = 0.75F * ret[COL_BACKGROUND * 3 + 2];
+
+    ret[COL_LOWLIGHT * 3 + 0] = ret[COL_BACKGROUND * 3 + 0] * 0.8F;
+    ret[COL_LOWLIGHT * 3 + 1] = ret[COL_BACKGROUND * 3 + 1] * 0.8F;
+    ret[COL_LOWLIGHT * 3 + 2] = ret[COL_BACKGROUND * 3 + 2] * 0.8F;
+    ret[COL_TEXT * 3 + 0] = 0.0;
+    ret[COL_TEXT * 3 + 1] = 0.0;
+    ret[COL_TEXT * 3 + 2] = 0.0;
+
+    return ret;
+}
+
+static void draw_filled_line(drawing *dr, int x1, int y1, int x2, int y2,
+                             int colour)
+{
+    draw_line(dr, x1-1, y1, x2-1, y2, COL_WIRE);
+    draw_line(dr, x1+1, y1, x2+1, y2, COL_WIRE);
+    draw_line(dr, x1, y1-1, x2, y2-1, COL_WIRE);
+    draw_line(dr, x1, y1+1, x2, y2+1, COL_WIRE);
+    draw_line(dr, x1, y1, x2, y2, colour);
+}
+
+static void draw_rect_coords(drawing *dr, int x1, int y1, int x2, int y2,
+                             int colour)
+{
+    int mx = (x1 < x2 ? x1 : x2);
+    int my = (y1 < y2 ? y1 : y2);
+    int dx = (x2 + x1 - 2*mx + 1);
+    int dy = (y2 + y1 - 2*my + 1);
+
+    draw_rect(dr, mx, my, dx, dy, colour);
+}
+
+static void draw_barrier_corner(drawing *dr, game_drawstate *ds,
+                                int x, int y, int dir, int phase)
+{
+    int bx = BORDER + WINDOW_OFFSET + TILE_SIZE * x;
+    int by = BORDER + WINDOW_OFFSET + TILE_SIZE * y;
+    int x1, y1, dx, dy, dir2;
+
+    dir >>= 4;
+
+    dir2 = A(dir);
+    dx = X(dir) + X(dir2);
+    dy = Y(dir) + Y(dir2);
+    x1 = (dx > 0 ? TILE_SIZE+TILE_BORDER-1 : 0);
+    y1 = (dy > 0 ? TILE_SIZE+TILE_BORDER-1 : 0);
+
+    if (phase == 0) {
+        draw_rect_coords(dr, bx+x1, by+y1,
+                         bx+x1-TILE_BORDER*dx, by+y1-(TILE_BORDER-1)*dy,
+                         COL_WIRE);
+        draw_rect_coords(dr, bx+x1, by+y1,
+                         bx+x1-(TILE_BORDER-1)*dx, by+y1-TILE_BORDER*dy,
+                         COL_WIRE);
+    } else {
+        draw_rect_coords(dr, bx+x1, by+y1,
+                         bx+x1-(TILE_BORDER-1)*dx, by+y1-(TILE_BORDER-1)*dy,
+                         COL_BARRIER);
+    }
+}
+
+static void draw_barrier(drawing *dr, game_drawstate *ds,
+                         int x, int y, int dir, int phase)
+{
+    int bx = BORDER + WINDOW_OFFSET + TILE_SIZE * x;
+    int by = BORDER + WINDOW_OFFSET + TILE_SIZE * y;
+    int x1, y1, w, h;
+
+    x1 = (X(dir) > 0 ? TILE_SIZE : X(dir) == 0 ? TILE_BORDER : 0);
+    y1 = (Y(dir) > 0 ? TILE_SIZE : Y(dir) == 0 ? TILE_BORDER : 0);
+    w = (X(dir) ? TILE_BORDER : TILE_SIZE - TILE_BORDER);
+    h = (Y(dir) ? TILE_BORDER : TILE_SIZE - TILE_BORDER);
+
+    if (phase == 0) {
+        draw_rect(dr, bx+x1-X(dir), by+y1-Y(dir), w, h, COL_WIRE);
+    } else {
+        draw_rect(dr, bx+x1, by+y1, w, h, COL_BARRIER);
+    }
+}
+
+static void draw_tile(drawing *dr, game_drawstate *ds, const game_state *state,
+                      int x, int y, int tile, float xshift, float yshift)
+{
+    int bx = BORDER + WINDOW_OFFSET + TILE_SIZE * x + (int)(xshift * TILE_SIZE);
+    int by = BORDER + WINDOW_OFFSET + TILE_SIZE * y + (int)(yshift * TILE_SIZE);
+    float cx, cy, ex, ey;
+    int dir, col;
+
+    /*
+     * When we draw a single tile, we must draw everything up to
+     * and including the borders around the tile. This means that
+     * if the neighbouring tiles have connections to those borders,
+     * we must draw those connections on the borders themselves.
+     *
+     * This would be terribly fiddly if we ever had to draw a tile
+     * while its neighbour was in mid-rotate, because we'd have to
+     * arrange to _know_ that the neighbour was being rotated and
+     * hence had an anomalous effect on the redraw of this tile.
+     * Fortunately, the drawing algorithm avoids ever calling us in
+     * this circumstance: we're either drawing lots of straight
+     * tiles at game start or after a move is complete, or we're
+     * repeatedly drawing only the rotating tile. So no problem.
+     */
+
+    /*
+     * So. First blank the tile out completely: draw a big
+     * rectangle in border colour, and a smaller rectangle in
+     * background colour to fill it in.
+     */
+    draw_rect(dr, bx, by, TILE_SIZE+TILE_BORDER, TILE_SIZE+TILE_BORDER,
+              COL_BORDER);
+    draw_rect(dr, bx+TILE_BORDER, by+TILE_BORDER,
+              TILE_SIZE-TILE_BORDER, TILE_SIZE-TILE_BORDER,
+              tile & FLASHING ? COL_FLASHING : COL_BACKGROUND);
+
+    /*
+     * Draw the wires.
+     */
+    cx = cy = TILE_BORDER + (TILE_SIZE-TILE_BORDER) / 2.0F - 0.5F;
+    col = (tile & ACTIVE ? COL_POWERED : COL_WIRE);
+    for (dir = 1; dir < 0x10; dir <<= 1) {
+        if (tile & dir) {
+            ex = (TILE_SIZE - TILE_BORDER - 1.0F) / 2.0F * X(dir);
+            ey = (TILE_SIZE - TILE_BORDER - 1.0F) / 2.0F * Y(dir);
+            draw_filled_line(dr, bx+(int)cx, by+(int)cy,
+                             bx+(int)(cx+ex), by+(int)(cy+ey),
+                             COL_WIRE);
+        }
+    }
+    for (dir = 1; dir < 0x10; dir <<= 1) {
+        if (tile & dir) {
+            ex = (TILE_SIZE - TILE_BORDER - 1.0F) / 2.0F * X(dir);
+            ey = (TILE_SIZE - TILE_BORDER - 1.0F) / 2.0F * Y(dir);
+            draw_line(dr, bx+(int)cx, by+(int)cy,
+                      bx+(int)(cx+ex), by+(int)(cy+ey), col);
+        }
+    }
+
+    /*
+     * Draw the box in the middle. We do this in blue if the tile
+     * is an unpowered endpoint, in cyan if the tile is a powered
+     * endpoint, in black if the tile is the centrepiece, and
+     * otherwise not at all.
+     */
+    col = -1;
+    if (x == state->cx && y == state->cy)
+        col = COL_WIRE;
+    else if (COUNT(tile) == 1) {
+        col = (tile & ACTIVE ? COL_POWERED : COL_ENDPOINT);
+    }
+    if (col >= 0) {
+        int i, points[8];
+
+        points[0] = +1; points[1] = +1;
+        points[2] = +1; points[3] = -1;
+        points[4] = -1; points[5] = -1;
+        points[6] = -1; points[7] = +1;
+
+        for (i = 0; i < 8; i += 2) {
+            ex = (TILE_SIZE * 0.24F) * points[i];
+            ey = (TILE_SIZE * 0.24F) * points[i+1];
+            points[i] = bx+(int)(cx+ex);
+            points[i+1] = by+(int)(cy+ey);
+        }
+
+        draw_polygon(dr, points, 4, col, COL_WIRE);
+    }
+
+    /*
+     * Draw the points on the border if other tiles are connected
+     * to us.
+     */
+    for (dir = 1; dir < 0x10; dir <<= 1) {
+        int dx, dy, px, py, lx, ly, vx, vy, ox, oy;
+
+        dx = X(dir);
+        dy = Y(dir);
+
+        ox = x + dx;
+        oy = y + dy;
+
+        if (ox < 0 || ox >= state->width || oy < 0 || oy >= state->height)
+            continue;
+
+        if (!(tile(state, ox, oy) & F(dir)))
+            continue;
+
+        px = bx + (int)(dx>0 ? TILE_SIZE + TILE_BORDER - 1 : dx<0 ? 0 : cx);
+        py = by + (int)(dy>0 ? TILE_SIZE + TILE_BORDER - 1 : dy<0 ? 0 : cy);
+        lx = dx * (TILE_BORDER-1);
+        ly = dy * (TILE_BORDER-1);
+        vx = (dy ? 1 : 0);
+        vy = (dx ? 1 : 0);
+
+        if (xshift == 0.0 && yshift == 0.0 && (tile & dir)) {
+            /*
+             * If we are fully connected to the other tile, we must
+             * draw right across the tile border. (We can use our
+             * own ACTIVE state to determine what colour to do this
+             * in: if we are fully connected to the other tile then
+             * the two ACTIVE states will be the same.)
+             */
+            draw_rect_coords(dr, px-vx, py-vy, px+lx+vx, py+ly+vy, COL_WIRE);
+            draw_rect_coords(dr, px, py, px+lx, py+ly,
+                             (tile & ACTIVE) ? COL_POWERED : COL_WIRE);
+        } else {
+            /*
+             * The other tile extends into our border, but isn't
+             * actually connected to us. Just draw a single black
+             * dot.
+             */
+            draw_rect_coords(dr, px, py, px, py, COL_WIRE);
+        }
+    }
+
+    draw_update(dr, bx, by, TILE_SIZE+TILE_BORDER, TILE_SIZE+TILE_BORDER);
+}
+
+static void draw_tile_barriers(drawing *dr, game_drawstate *ds,
+                               const game_state *state, int x, int y)
+{
+    int phase;
+    int dir;
+    int bx = BORDER + WINDOW_OFFSET + TILE_SIZE * x;
+    int by = BORDER + WINDOW_OFFSET + TILE_SIZE * y;
+    /*
+     * Draw barrier corners, and then barriers.
+     */
+    for (phase = 0; phase < 2; phase++) {
+        for (dir = 1; dir < 0x10; dir <<= 1)
+            if (barrier(state, x, y) & (dir << 4))
+                draw_barrier_corner(dr, ds, x, y, dir << 4, phase);
+        for (dir = 1; dir < 0x10; dir <<= 1)
+            if (barrier(state, x, y) & dir)
+                draw_barrier(dr, ds, x, y, dir, phase);
+    }
+
+    draw_update(dr, bx, by, TILE_SIZE+TILE_BORDER, TILE_SIZE+TILE_BORDER);
+}
+
+static void draw_arrow(drawing *dr, game_drawstate *ds,
+                       int x, int y, int xdx, int xdy, int cur)
+{
+    int coords[14];
+    int ydy = -xdx, ydx = xdy;
+
+    x = x * TILE_SIZE + BORDER + WINDOW_OFFSET;
+    y = y * TILE_SIZE + BORDER + WINDOW_OFFSET;
+
+#define POINT(n, xx, yy) ( \
+    coords[2*(n)+0] = x + (xx)*xdx + (yy)*ydx, \
+    coords[2*(n)+1] = y + (xx)*xdy + (yy)*ydy)
+
+    POINT(0, TILE_SIZE / 2, 3 * TILE_SIZE / 4);   /* top of arrow */
+    POINT(1, 3 * TILE_SIZE / 4, TILE_SIZE / 2);   /* right corner */
+    POINT(2, 5 * TILE_SIZE / 8, TILE_SIZE / 2);   /* right concave */
+    POINT(3, 5 * TILE_SIZE / 8, TILE_SIZE / 4);   /* bottom right */
+    POINT(4, 3 * TILE_SIZE / 8, TILE_SIZE / 4);   /* bottom left */
+    POINT(5, 3 * TILE_SIZE / 8, TILE_SIZE / 2);   /* left concave */
+    POINT(6,     TILE_SIZE / 4, TILE_SIZE / 2);   /* left corner */
+
+    draw_polygon(dr, coords, 7, cur ? COL_POWERED : COL_LOWLIGHT, COL_TEXT);
+}
+
+static void draw_arrow_for_cursor(drawing *dr, game_drawstate *ds,
+                                  int cur_x, int cur_y, int cur)
+{
+    if (cur_x == -1 && cur_y == -1)
+        return; /* 'no cursur here */
+    else if (cur_x == -1) /* LH column. */
+        draw_arrow(dr, ds, 0, cur_y+1, 0, -1, cur);
+    else if (cur_x == ds->width) /* RH column */
+        draw_arrow(dr, ds, ds->width, cur_y, 0, +1, cur);
+    else if (cur_y == -1) /* Top row */
+        draw_arrow(dr, ds, cur_x, 0, +1, 0, cur);
+    else if (cur_y == ds->height) /* Bottom row */
+        draw_arrow(dr, ds, cur_x+1, ds->height, -1, 0, cur);
+    else
+        assert(!"Invalid cursor position");
+
+    draw_update(dr,
+                cur_x * TILE_SIZE + BORDER + WINDOW_OFFSET,
+                cur_y * TILE_SIZE + BORDER + WINDOW_OFFSET,
+                TILE_SIZE, TILE_SIZE);
+}
+
+static void game_redraw(drawing *dr, game_drawstate *ds,
+                        const game_state *oldstate, const game_state *state,
+                        int dir, const game_ui *ui,
+                        float t, float ft)
+{
+    int x, y, frame;
+    unsigned char *active;
+    float xshift = 0.0;
+    float yshift = 0.0;
+    int cur_x = -1, cur_y = -1;
+
+    /*
+     * Clear the screen and draw the exterior barrier lines if this
+     * is our first call.
+     */
+    if (!ds->started) {
+        int phase;
+
+        ds->started = TRUE;
+
+        draw_rect(dr, 0, 0, 
+                  BORDER * 2 + WINDOW_OFFSET * 2 + TILE_SIZE * state->width + TILE_BORDER,
+                  BORDER * 2 + WINDOW_OFFSET * 2 + TILE_SIZE * state->height + TILE_BORDER,
+                  COL_BACKGROUND);
+        draw_update(dr, 0, 0, 
+                    BORDER * 2 + WINDOW_OFFSET*2 + TILE_SIZE*state->width + TILE_BORDER,
+                    BORDER * 2 + WINDOW_OFFSET*2 + TILE_SIZE*state->height + TILE_BORDER);
+
+        for (phase = 0; phase < 2; phase++) {
+
+            for (x = 0; x < ds->width; x++) {
+                if (barrier(state, x, 0) & UL)
+                    draw_barrier_corner(dr, ds, x, -1, LD, phase);
+                if (barrier(state, x, 0) & RU)
+                    draw_barrier_corner(dr, ds, x, -1, DR, phase);
+                if (barrier(state, x, 0) & U)
+                    draw_barrier(dr, ds, x, -1, D, phase);
+                if (barrier(state, x, ds->height-1) & DR)
+                    draw_barrier_corner(dr, ds, x, ds->height, RU, phase);
+                if (barrier(state, x, ds->height-1) & LD)
+                    draw_barrier_corner(dr, ds, x, ds->height, UL, phase);
+                if (barrier(state, x, ds->height-1) & D)
+                    draw_barrier(dr, ds, x, ds->height, U, phase);
+            }
+
+            for (y = 0; y < ds->height; y++) {
+                if (barrier(state, 0, y) & UL)
+                    draw_barrier_corner(dr, ds, -1, y, RU, phase);
+                if (barrier(state, 0, y) & LD)
+                    draw_barrier_corner(dr, ds, -1, y, DR, phase);
+                if (barrier(state, 0, y) & L)
+                    draw_barrier(dr, ds, -1, y, R, phase);
+                if (barrier(state, ds->width-1, y) & RU)
+                    draw_barrier_corner(dr, ds, ds->width, y, UL, phase);
+                if (barrier(state, ds->width-1, y) & DR)
+                    draw_barrier_corner(dr, ds, ds->width, y, LD, phase);
+                if (barrier(state, ds->width-1, y) & R)
+                    draw_barrier(dr, ds, ds->width, y, L, phase);
+            }
+        }
+
+        /*
+         * Arrows for making moves.
+         */
+        for (x = 0; x < ds->width; x++) {
+            if (x == state->cx) continue;
+            draw_arrow(dr, ds, x, 0, +1, 0, 0);
+            draw_arrow(dr, ds, x+1, ds->height, -1, 0, 0);
+        }
+        for (y = 0; y < ds->height; y++) {
+            if (y == state->cy) continue;
+            draw_arrow(dr, ds, ds->width, y, 0, +1, 0);
+            draw_arrow(dr, ds, 0, y+1, 0, -1, 0);
+        }
+    }
+    if (ui->cur_visible) {
+        cur_x = ui->cur_x; cur_y = ui->cur_y;
+    }
+    if (cur_x != ds->cur_x || cur_y != ds->cur_y) {
+        /* Cursor has changed; redraw two (prev and curr) arrows. */
+        assert(cur_x != state->cx && cur_y != state->cy);
+
+        draw_arrow_for_cursor(dr, ds, cur_x, cur_y, 1);
+        draw_arrow_for_cursor(dr, ds, ds->cur_x, ds->cur_y, 0);
+        ds->cur_x = cur_x; ds->cur_y = cur_y;
+    }
+
+    /* Check if this is an undo.  If so, we will need to run any animation
+     * backwards.
+     */
+    if (oldstate && oldstate->move_count > state->move_count) {
+        const game_state * tmpstate = state;
+        state = oldstate;
+        oldstate = tmpstate;
+        t = ANIM_TIME - t;
+    }
+
+    if (oldstate && (t < ANIM_TIME)) {
+        /*
+         * We're animating a slide, of row/column number
+         * state->last_move_pos, in direction
+         * state->last_move_dir
+         */
+        xshift = state->last_move_row == -1 ? 0.0F :
+                (1 - t / ANIM_TIME) * state->last_move_dir;
+        yshift = state->last_move_col == -1 ? 0.0F :
+                (1 - t / ANIM_TIME) * state->last_move_dir;
+    }
+    
+    frame = -1;
+    if (ft > 0) {
+        /*
+         * We're animating a completion flash. Find which frame
+         * we're at.
+         */
+        frame = (int)(ft / FLASH_FRAME);
+    }
+
+    /*
+     * Draw any tile which differs from the way it was last drawn.
+     */
+    if (xshift != 0.0 || yshift != 0.0) {
+        active = compute_active(state,
+                                state->last_move_row, state->last_move_col);
+    } else {
+        active = compute_active(state, -1, -1);
+    }
+
+    clip(dr,
+         BORDER + WINDOW_OFFSET, BORDER + WINDOW_OFFSET,
+         TILE_SIZE * state->width + TILE_BORDER,
+         TILE_SIZE * state->height + TILE_BORDER);
+    
+    for (x = 0; x < ds->width; x++)
+        for (y = 0; y < ds->height; y++) {
+            unsigned char c = tile(state, x, y) | index(state, active, x, y);
+
+            /*
+             * In a completion flash, we adjust the FLASHING bit
+             * depending on our distance from the centre point and
+             * the frame number.
+             */
+            if (frame >= 0) {
+                int xdist, ydist, dist;
+                xdist = (x < state->cx ? state->cx - x : x - state->cx);
+                ydist = (y < state->cy ? state->cy - y : y - state->cy);
+                dist = (xdist > ydist ? xdist : ydist);
+
+                if (frame >= dist && frame < dist+4) {
+                    int flash = (frame - dist) & 1;
+                    flash = flash ? FLASHING : 0;
+                    c = (c &~ FLASHING) | flash;
+                }
+            }
+
+            if (index(state, ds->visible, x, y) != c ||
+                index(state, ds->visible, x, y) == 0xFF ||
+                (x == state->last_move_col || y == state->last_move_row))
+            {
+                float xs = (y == state->last_move_row ? xshift : (float)0.0);
+                float ys = (x == state->last_move_col ? yshift : (float)0.0);
+
+                draw_tile(dr, ds, state, x, y, c, xs, ys);
+                if (xs < 0 && x == 0)
+                    draw_tile(dr, ds, state, state->width, y, c, xs, ys);
+                else if (xs > 0 && x == state->width - 1)
+                    draw_tile(dr, ds, state, -1, y, c, xs, ys);
+                else if (ys < 0 && y == 0)
+                    draw_tile(dr, ds, state, x, state->height, c, xs, ys);
+                else if (ys > 0 && y == state->height - 1)
+                    draw_tile(dr, ds, state, x, -1, c, xs, ys);
+
+                if (x == state->last_move_col || y == state->last_move_row)
+                    index(state, ds->visible, x, y) = 0xFF;
+                else
+                    index(state, ds->visible, x, y) = c;
+            }
+        }
+
+    for (x = 0; x < ds->width; x++)
+        for (y = 0; y < ds->height; y++)
+            draw_tile_barriers(dr, ds, state, x, y);
+
+    unclip(dr);
+
+    /*
+     * Update the status bar.
+     */
+    {
+        char statusbuf[256];
+        int i, n, a;
+
+        n = state->width * state->height;
+        for (i = a = 0; i < n; i++)
+            if (active[i])
+                a++;
+
+        if (state->used_solve)
+            sprintf(statusbuf, "Moves since auto-solve: %d",
+                    state->move_count - state->completed);
+        else
+            sprintf(statusbuf, "%sMoves: %d",
+                    (state->completed ? "COMPLETED! " : ""),
+                    (state->completed ? state->completed : state->move_count));
+
+        if (state->movetarget)
+            sprintf(statusbuf + strlen(statusbuf), " (target %d)",
+                    state->movetarget);
+
+        sprintf(statusbuf + strlen(statusbuf), " Active: %d/%d", a, n);
+
+        status_bar(dr, statusbuf);
+    }
+
+    sfree(active);
+}
+
+static float game_anim_length(const game_state *oldstate,
+                              const game_state *newstate, int dir, game_ui *ui)
+{
+    return ANIM_TIME;
+}
+
+static float game_flash_length(const game_state *oldstate,
+                               const game_state *newstate, int dir, game_ui *ui)
+{
+    /*
+     * If the game has just been completed, we display a completion
+     * flash.
+     */
+    if (!oldstate->completed && newstate->completed &&
+        !oldstate->used_solve && !newstate->used_solve) {
+        int size;
+        size = 0;
+        if (size < newstate->cx+1)
+            size = newstate->cx+1;
+        if (size < newstate->cy+1)
+            size = newstate->cy+1;
+        if (size < newstate->width - newstate->cx)
+            size = newstate->width - newstate->cx;
+        if (size < newstate->height - newstate->cy)
+            size = newstate->height - newstate->cy;
+        return FLASH_FRAME * (size+4);
+    }
+
+    return 0.0F;
+}
+
+static int game_status(const game_state *state)
+{
+    return state->completed ? +1 : 0;
+}
+
+static int game_timing_state(const game_state *state, game_ui *ui)
+{
+    return FALSE;
+}
+
+static void game_print_size(const game_params *params, float *x, float *y)
+{
+}
+
+static void game_print(drawing *dr, const game_state *state, int tilesize)
+{
+}
+
+#ifdef COMBINED
+#define thegame netslide
+#endif
+
+const struct game thegame = {
+    "Netslide", "games.netslide", "netslide",
+    default_params,
+    game_fetch_preset, NULL,
+    decode_params,
+    encode_params,
+    free_params,
+    dup_params,
+    TRUE, game_configure, custom_params,
+    validate_params,
+    new_game_desc,
+    validate_desc,
+    new_game,
+    dup_game,
+    free_game,
+    TRUE, solve_game,
+    FALSE, game_can_format_as_text_now, game_text_format,
+    new_ui,
+    free_ui,
+    encode_ui,
+    decode_ui,
+    game_changed_state,
+    interpret_move,
+    execute_move,
+    PREFERRED_TILE_SIZE, game_compute_size, game_set_size,
+    game_colours,
+    game_new_drawstate,
+    game_free_drawstate,
+    game_redraw,
+    game_anim_length,
+    game_flash_length,
+    game_status,
+    FALSE, FALSE, game_print_size, game_print,
+    TRUE,                              /* wants_statusbar */
+    FALSE, game_timing_state,
+    0,                                 /* flags */
+};
+
+/* vim: set shiftwidth=4 tabstop=8: */