More forgiving selection of dragging targets.

git-svn-id: svn://svn.tartarus.org/sgt/puzzles@7574 cda61777-01e9-0310-a592-d414129be87e

diff --git a/unfinished/slide.c b/unfinished/slide.c
index 8a954a3..84639ed 100644 (file)
--- a/unfinished/slide.c
+++ b/unfinished/slide.c
@@ -5,9 +5,6 @@
 /*
  * TODO:
  * 
- *  - The dragging semantics are still subtly wrong in complex
- *    cases.
- * 
  *  - Improve the generator.
  *     * actually, we seem to be mostly sensible already now. I
  *      want more choice over the type of main block and location
@@ -1345,17 +1342,36 @@ static char *interpret_move(game_state *state, game_ui *ui, game_drawstate *ds,
         */
        return "";
     } else if (button == LEFT_DRAG && ui->dragging) {
+       int dist, distlimit, dx, dy, s, px, py;
+
        tx = FROMCOORD(x);
        ty = FROMCOORD(y);
 
        tx -= ui->drag_offset_x;
        ty -= ui->drag_offset_y;
-       if (tx < 0 || tx >= w || ty < 0 || ty >= h ||
-           !ui->reachable[ty*w+tx])
-           return NULL;               /* this drag has no effect */
 
-       ui->drag_currpos = ty*w+tx;
-       return "";
+       /*
+        * Now search outwards from (tx,ty), in order of Manhattan
+        * distance, until we find a reachable square.
+        */
+       distlimit = w+tx;
+       distlimit = max(distlimit, h+ty);
+       distlimit = max(distlimit, tx);
+       distlimit = max(distlimit, ty);
+       for (dist = 0; dist <= distlimit; dist++) {
+           for (dx = -dist; dx <= dist; dx++)
+               for (s = -1; s <= +1; s += 2) {
+                   dy = s * (dist - abs(dx));
+                   px = tx + dx;
+                   py = ty + dy;
+                   if (px >= 0 && px < w && py >= 0 && py < h &&
+                       ui->reachable[py*w+px]) {
+                       ui->drag_currpos = py*w+px;
+                       return "";
+                   }
+               }
+       }
+       return NULL;                   /* give up - this drag has no effect */
     } else if (button == LEFT_RELEASE && ui->dragging) {
        char data[256], *str;