On Thu, Jul 5, 2012 at 1:05 PM, Edward O'Connor <eocon...@apple.com> wrote: > As things currently stand in the spec, implementations basically need to > keep N+1 bitmaps per canvas, where N is the number of hit regions. I > doubt any implementors would be enthusiastic to implement hit regions > like this. From a WebKit perspective, we'd much prefer keeping a Path > for each hit region, and then simply using isPointInPath for hit > testing. This also implies that the current piggybacking of "Clear > regions that cover the pixels" in clearRect() could go away. Yay! :)
Bog-standard hit-testing algorithms apply. Keep a single extra canvas around, draw each region into it with a different color. When you're hit-testing, just see what color that pixel is, and look up which region is associated with it. This is extremely fast and simple to implement, and has all the right properties - the "topmost" region for a given pixel is the one returned. ~TJ
