Ticket #3944: collision.patch

src/jarabe/desktop/grid.py

@@ -197 +197 @@
     def _detect_collisions(self, child):
         collision_found = False
         child_rect = self._child_rects[child]
+
+        # Look at all of the other grid children, to see if child conflicts
+        # with them. If so, try to move one of the children involved in the
+        # collision.
         for c in self._children:
+            if c == child:
+                continue
+
             intersects_, intersection = Gdk.rectangle_intersect(
                 child_rect, self._child_rects[c])
-            if c != child and intersection.width > 0:
-                if (c not in self._locked_children and
-                    c not in self._collisions):
-                    collision_found = True
+            if intersection.width == 0:
+                # No collision
+                continue
+
+            # We found a collision - now we try to act on it
+            child_locked = child in self._locked_children
+            c_locked = c in self._locked_children
+
+            # If both children involved in the collision are locked, lets
+            # just let them collide.
+            if c_locked and child_locked:
+                continue
+
+            # If the child is locked, lets move the unlocked colliding c
+            # somewhere else
+            if child_locked:
+                if c not in self._collisions:
                     self._collisions.append(c)
-
-        if collision_found:
-            if child not in self._collisions:
-                self._collisions.append(child)
+                continue
+
+            # We are dealing with a collision where child is not locked.
+            # If it collides with a locked c, we try to reposition child,
+            # as the locked one should "win" for obvious reasons.
+            # If c is not locked, we similarly decide to move child to solve,
+            # the collision, on the basis that c got there first so child
+            # should be the one that moves around, reducing UI disruption.
+            self._collisions.append(child)
+
+            # Now we break out early; as we're about to re-position child,
+            # it doesn't make any sense to continue looking for more
+            # collisions with it.
+            break
 
         if self._collisions and not self._collisions_sid:
             self._collisions_sid = GObject.timeout_add(_REFRESH_RATE,