Layer squashing prototype

[shawnsingh, 2013-03-21 04:54:40]

PTAL

In particular, please give feedback on the overall design.  I still need to
address performance and some bugs.  Thanks!

[shawnsingh, 2013-03-21 05:01:02]

https://codereview.appspot.com/7625051/diff/2001/Source/WebCore/rendering/Ren...
File Source/WebCore/rendering/RenderLayerBacking.cpp (right):

https://codereview.appspot.com/7625051/diff/2001/Source/WebCore/rendering/Ren...
Source/WebCore/rendering/RenderLayerBacking.cpp:1383: phase &=
~(GraphicsLayerPaintForeground & GraphicsLayerPaintOverlap);
Actually I think this should be bitwise OR |  instead of AND &.

[vollick, 2013-03-21 17:21:01]

Nicely done! This patch seems very reasonable to me.

https://codereview.appspot.com/7625051/diff/8001/Source/WebCore/rendering/Ren...
File Source/WebCore/rendering/RenderLayer.cpp (right):

https://codereview.appspot.com/7625051/diff/8001/Source/WebCore/rendering/Ren...
Source/WebCore/rendering/RenderLayer.cpp:3928: if
(childLayer->shouldPaintDuringOverlapPhase() && !(paintFlags &
PaintLayerPaintingCompositingOverlapPhase))
nit: If the logic goes this way, I'd suggest the name
shouldOnlyPaintDuringOverlapPhase

https://codereview.appspot.com/7625051/diff/8001/Source/WebCore/rendering/Ren...
File Source/WebCore/rendering/RenderLayerCompositor.cpp (right):

https://codereview.appspot.com/7625051/diff/8001/Source/WebCore/rendering/Ren...
Source/WebCore/rendering/RenderLayerCompositor.cpp:1045: : true)) {
This is very tough to follow. Please build up the should-use-an-overlap-layer
boolean over several lines rather than using all these ternary operators.

[hartmanng, 2013-03-21 17:43:19]

+1 to Ian's comments, and another tiny nit, overall plan lgtm though!

https://codereview.appspot.com/7625051/diff/8001/Source/WebCore/rendering/Ren...
File Source/WebCore/rendering/RenderLayerCompositor.cpp (right):

https://codereview.appspot.com/7625051/diff/8001/Source/WebCore/rendering/Ren...
Source/WebCore/rendering/RenderLayerCompositor.cpp:510: TRACE_EVENT0("WebCore",
"computeCompositingRequirements()");
nit: redundant trace events, you can just move these outside the if block
(unless you're planning on modifying them to tell them apart)