🚀 go-pugleaf

 If you want to catch mouse down events that hit, or nearly hit, 
parts of your drawings do not use regions.
  Regions are very memory intensive.  They are a scan line
representation.  The only compression is for vertical rectangular
sections.  The incremenal cost of building up a complex region
is almost always very high because it causes a lot of memory
manager thrashing.
  A very tractable way to check for a mouse down on your drawing
is to draw it into an off screen bit map.  Watch that bit
map for any bits near the mouse changing.
  The offscreen bit map maybe very small, and you can offset it
until only the area around the mouse is actually being filled out.
  Real power pixel people might grab the bottle neck procs and
modify the drawing stream to only use black paint.
  This is very very fast.  In one of my applications I do it inside
the event loop to change cursor shape dynamicly.  It works well for
hundred part drawings.
   - ben hyde, cambridge