tree f0d9b4d0d585c098249019b61717ae050440e4fa
parent 13a4e86f9805ee8595db991a26eb0211c7c172ff
author simon.fraser@apple.com <simon.fraser@apple.com@268f45cc-cd09-0410-ab3c-d52691b4dbfc> 1558274475 +0000
committer simon.fraser@apple.com <simon.fraser@apple.com@268f45cc-cd09-0410-ab3c-d52691b4dbfc> 1558274475 +0000

Layers painting into shared backing need to contribute to overlap
https://bugs.webkit.org/show_bug.cgi?id=198021

Reviewed by Zalan Bujtas.
Source/WebCore:

Layers that paint into a composited (non-root) layer get added to the overlap map so
that later layers correct overlap them; this is done via the test against currentState.compositingAncestor.

We need the same logic for layers that paint into shared backing; they need to behave
the same way in terms of how they contribute to overlap. We already had currentState.backingSharingAncestor
which was unused, but now use it for this, and correctly null it out when a layer composites.

Bug was noticed during testing, and not known to affect any websites (though it probably does).

Also move the overlap container popping into updateOverlapMap() so the two callers can
share the code, and more explicitly track whether a container was pushed.

Test: compositing/shared-backing/sharing-child-contributes-to-overlap.html

* rendering/RenderLayerCompositor.cpp:
(WebCore::RenderLayerCompositor::computeCompositingRequirements):
(WebCore::RenderLayerCompositor::traverseUnchangedSubtree):
(WebCore::RenderLayerCompositor::updateOverlapMap const):
* rendering/RenderLayerCompositor.h:

LayoutTests:

* compositing/shared-backing/sharing-child-contributes-to-overlap-expected.html: Added.
* compositing/shared-backing/sharing-child-contributes-to-overlap.html: Added.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@245502 268f45cc-cd09-0410-ab3c-d52691b4dbfc