[haiku-bugs] [Haiku] #10877: ClipToPicture is too slow

  • From: "pulkomandy" <trac@xxxxxxxxxxxx>
  • Date: Tue, 27 May 2014 07:22:05 -0000

#10877: ClipToPicture is too slow
 Reporter:  pulkomandy          |        Owner:  stippi
     Type:  enhancement         |       Status:  new
 Priority:  normal              |    Milestone:  R1
Component:  Servers/app_server  |      Version:  R1/Development
 Keywords:                      |   Blocked By:
 Blocking:                      |  Has a Patch:  0
 Platform:  All                 |
 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.

Ticket URL: <https://dev.haiku-os.org/ticket/10877>
Haiku <https://dev.haiku-os.org>
Haiku - the operating system.

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