Merge pull request kivy#1797 from matham/scatter-fix

Fix scatter issues

Author: tshirtman

kivy/uix/scatter.py

@@ -415,24 +415,29 @@ def transform_with_touch(self, touch):
         if len(self._touches) == 1:
             return changed
 
-        # we have more than one touch...
-        points = [Vector(self._last_touch_pos[t]) for t in self._touches]
+        # we have more than one touch... list of last known pos
+        points = [Vector(self._last_touch_pos[t]) for t in self._touches
+                  if t is not touch]
+        # add current touch last
+        points.append(Vector(touch.pos))
 
         # we only want to transform if the touch is part of the two touches
-        # furthest apart! So first we find anchor, the point to transform
-        # around as the touch farthest away from touch
-        anchor = max(points, key=lambda p: p.distance(touch.pos))
+        # farthest apart! So first we find anchor, the point to transform
+        # around as another touch farthest away from current touch's pos
+        anchor = max(points[:-1], key=lambda p: p.distance(touch.pos))
 
         # now we find the touch farthest away from anchor, if its not the
         # same as touch. Touch is not one of the two touches used to transform
         farthest = max(points, key=anchor.distance)
-        if points.index(farthest) != self._touches.index(touch):
+        if farthest is not points[-1]:
             return changed
 
         # ok, so we have touch, and anchor, so we can actually compute the
         # transformation
         old_line = Vector(*touch.ppos) - anchor
         new_line = Vector(*touch.pos) - anchor
+        if not old_line.length():   # div by zero
+            return changed
 
         angle = radians(new_line.angle(old_line)) * self.do_rotation
         self.apply_transform(Matrix().rotate(angle, 0, 0, 1), anchor=anchor)