#10877: ClipToPicture is too slow
----------------------------------+----------------------------
Reporter: pulkomandy | Owner: stippi
Type: enhancement | Status: closed
Priority: normal | Milestone: R1
Component: Servers/app_server | Version: R1/Development
Resolution: fixed | Keywords:
Blocked By: | Blocking:
Has a Patch: 0 | Platform: All
----------------------------------+----------------------------
Changes (by pulkomandy):
* status: new => closed
* resolution: => fixed
Old description:
We now have a working implementation of ClipToPicture. It is the only way
to perform clipping in the transformed view space
(ConstrainClippingRegion does not work with transforms). However,
ClipToPicture hit tests work by alpha blending pixels, which is slow.
WebKit makes heavy use of that feature which makes it painful to use. We
have to make this work faster.
An idea is to compute the un-transformed bounds of the clipping picture
covered area, and use rectangle clipping to exclude anything outside that
area from the drawing. When using a big view and a small clipping
picture, this could cut down the time a lot. This extra clipping
rectangle needs to be computed whenever the AlphaMask is generated, as
changes in the view state could lead to different results.
Maybe there are other ways to improve this on the drawing side: avoiding
the alpha blending when the clipping picture is only made of fully opaque
or fully transparent pixels, for example? This may needs changes to agg
rasterizer code.
