[OpenLayers-Dev] canvas hit detection simplification
tschaub at opengeo.org
Fri Apr 1 19:19:47 EDT 2011
There's one additional change I'd like to get in regarding the hit
detection in canvas. It's a fairly big simplification that lets us
avoid a same origin constraint on external graphics.
Currently, when the user styles a point with an external graphic, we
render this graphic to a dedicated graphic hit canvas and then render
just the visible pixels with an identifiable color to the main hit
canvas. This has the benefit of only counting hits when an event
coincides with a non-transparent pixel in the external graphic. The
drawbacks are that it brings extra overhead and limits external graphics
to the same origin policy.
The hit detection for external graphics can be simplified by rendering a
rectangle on the hit canvas that is the same size as the graphic on the
display canvas. With this method, we get rid of extra pixel manipulation
and avoid same origin constraints.
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