Calculate pattern bounds correctly

Use stable position on screen to calculate if pattern should be
dragged or not. Before we were only comparing bounds to events,
that would be on different coordinates (on a parent for example.)

Test: draw pattern starting at top left
Test: draw pattern starting at bottom right
Fixes: 132687980
Change-Id: Ibe2d7fc113bf8bc3a9ab4910b3ab21062b59e7f3