+ for (i = 0; i < state->n; i++) {
+ int t, t0;
+ /*
+ * Figure out what should be displayed at this
+ * location. It's either a simple tile, or it's a
+ * transition between two tiles (in which case we say
+ * -1 because it must always be drawn).
+ */
+
+ if (oldstate && oldstate->tiles[i] != state->tiles[i])
+ t = -1;
+ else
+ t = state->tiles[i];
+
+ t0 = t;
+
+ if (ds->bgcolour != bgcolour || /* always redraw when flashing */
+ ds->tiles[i] != t || ds->tiles[i] == -1 || t == -1) {
+ int x, y, x2, y2;
+
+ /*
+ * Figure out what to _actually_ draw, and where to
+ * draw it.
+ */
+ if (t == -1) {
+ int x0, y0, x1, y1, dx, dy;
+ int j;
+ float c;
+ int sense;
+
+ if (dir < 0) {
+ assert(oldstate);
+ sense = -oldstate->last_movement_sense;
+ } else {
+ sense = state->last_movement_sense;
+ }
+
+ t = state->tiles[i];
+
+ /*
+ * FIXME: must be prepared to draw a double
+ * tile in some situations.
+ */
+
+ /*
+ * Find the coordinates of this tile in the old and
+ * new states.
+ */
+ x1 = COORD(X(state, i));
+ y1 = COORD(Y(state, i));
+ for (j = 0; j < oldstate->n; j++)
+ if (oldstate->tiles[j] == state->tiles[i])
+ break;
+ assert(j < oldstate->n);
+ x0 = COORD(X(state, j));
+ y0 = COORD(Y(state, j));
+
+ dx = (x1 - x0);
+ if (dx != 0 &&
+ dx != TILE_SIZE * sense) {
+ dx = (dx < 0 ? dx + TILE_SIZE * state->w :
+ dx - TILE_SIZE * state->w);
+ assert(abs(dx) == TILE_SIZE);
+ }
+ dy = (y1 - y0);
+ if (dy != 0 &&
+ dy != TILE_SIZE * sense) {
+ dy = (dy < 0 ? dy + TILE_SIZE * state->h :
+ dy - TILE_SIZE * state->h);
+ assert(abs(dy) == TILE_SIZE);
+ }
+
+ c = (animtime / ANIM_TIME);
+ if (c < 0.0F) c = 0.0F;
+ if (c > 1.0F) c = 1.0F;
+
+ x = x0 + (int)(c * dx);
+ y = y0 + (int)(c * dy);
+ x2 = x1 - dx + (int)(c * dx);
+ y2 = y1 - dy + (int)(c * dy);
+ } else {
+ x = COORD(X(state, i));
+ y = COORD(Y(state, i));
+ x2 = y2 = -1;
+ }
+
+ draw_tile(dr, ds, state, x, y, t, bgcolour);
+ if (x2 != -1 || y2 != -1)
+ draw_tile(dr, ds, state, x2, y2, t, bgcolour);
+ }
+ ds->tiles[i] = t0;