+hit_in_square(Sprite *r, Sprite *s)
+{
+ for(; r; r=r->next) {
+ if(collide(r, s)) return true;
+ }
+ return false;
+}
+
+int
+collides(Sprite *s)
+{
+ int l, r, t, b;
+ Sprite **sq;
+
+ l = (s->x + grid_size) / grid_size;
+ r = (s->x + s->w + grid_size) / grid_size;
+ t = (s->y + grid_size) / grid_size;
+ b = (s->y + s->h + grid_size) / grid_size;
+ sq = &sprites[set][l + t*gw];
+
+ if(hit_in_square(*sq, s)) return true;
+ if(l > 0 && hit_in_square(*(sq-1), s)) return true;
+ if(t > 0 && hit_in_square(*(sq-gw), s)) return true;
+ if(l > 0 && t > 0 && hit_in_square(*(sq-1-gw), s)) return true;
+
+ if(r > l) {
+ if(hit_in_square(*(sq+1), s)) return true;
+ if(t > 0 && hit_in_square(*(sq+1-gw), s)) return true;
+ }
+ if(b > t) {
+ if(hit_in_square(*(sq+gw), s)) return true;
+ if(l > 0 && hit_in_square(*(sq-1+gw), s)) return true;
+ }
+ if(r > l && b > t && hit_in_square(*(sq+1+gw), s)) return true;
+ return false;
+}
+
+int
+pixel_collide(Sprite *s, int x, int y)