commit 9480b4c29caad4f4bd070e35111d9a03e53a3337
author simon.fraser@apple.com <simon.fraser@apple.com@268f45cc-cd09-0410-ab3c-d52691b4dbfc> Wed May 22 00:12:49 2019 +0000
committer simon.fraser@apple.com <simon.fraser@apple.com@268f45cc-cd09-0410-ab3c-d52691b4dbfc> Wed May 22 00:12:49 2019 +0000
tree 8c941e2e3d3582bf7aea8f0d383325a3725941a1
parent 058b39402984831eed74663d6ad6d576aa5a3086

Layer flashing and poor perf during scrolling of message list on gmail.com and hotmail.com - overlap testing needs to constrained to clipping scopes
https://bugs.webkit.org/show_bug.cgi?id=198091
<rdar://problem/49403082>

Reviewed by Antti Koivisto.
Source/WebCore:

When overflow:scroll is scrolled asynchronously, we need to have already created compositing layers where necessary
for clipped-out layers in the scrolled content so that we have something to reveal. We also have ensure
that layers inside the scroller (but scrolled out of view) don't trigger overlap with layers outside the scroller.
All this has to work when the containing block hierarchy (clipping/scrolling) doesn't match the paint order hierarchy (structure
of the z-order and compositing trees).

Overlap testing previously simply used a list of rectangles per compositing container (OverlapMapContainer). This is
a series of layer bounds, built up as we traver the layer tree in z-order. Layers contribute to container N-2, and test
against container N-1.

To handle overlap with non-stacking-context scrollers, introduce the concept of a ClippingScope, which encompasses
a set of layers sharing the same composited-scrolling containing-block ancestor. Within a ClippingScope, layer bounds
are computed unclipped. Between them, bounds are tested clipped.

Conceptually, each OverlapMapContainer has a tree of ClippingScopes (reflecting the containing-block order tree of
composited overflow scroll), and rects are added to the appropriate ClippingScope. This tree is currently always
root-relative; the root node is the RenderView's RenderLayer, and will accumulate the bounds of layers not inside
composited overflow scroll (just like the old code).

When a OverlapMapContainer is popped, the list of rectangles in its ClippingScope tree is merged with that of the previous
container.

Tests: compositing/layer-creation/clipping-scope/nested-scroller-overlap.html
       compositing/layer-creation/clipping-scope/overlap-constrained-inside-scroller.html
       compositing/layer-creation/clipping-scope/overlap-constrained-inside-stacking-context-scroller.html
       compositing/layer-creation/clipping-scope/scroller-with-negative-z-children.html
       compositing/layer-creation/clipping-scope/shared-layers-in-scroller.html

* rendering/LayerOverlapMap.cpp:
(WebCore::operator<<):
(WebCore::OverlapMapContainer::OverlapMapContainer):
(WebCore::OverlapMapContainer::ClippingScope::ClippingScope):
(WebCore::OverlapMapContainer::ClippingScope::childWithLayer const):
(WebCore::OverlapMapContainer::ClippingScope::addChildWithLayerAndBounds):
(WebCore::OverlapMapContainer::ClippingScope::addChild):
(WebCore::OverlapMapContainer::ClippingScope::appendRect):
(WebCore::OverlapMapContainer::clippingScopeContainingLayerChildRecursive):
(WebCore::OverlapMapContainer::scopeContainingLayer const):
(WebCore::OverlapMapContainer::rootScope const):
(WebCore::OverlapMapContainer::rootScope):
(WebCore::OverlapMapContainer::add):
(WebCore::OverlapMapContainer::overlapsLayers const):
(WebCore::OverlapMapContainer::mergeClippingScopesRecursive):
(WebCore::OverlapMapContainer::append):
(WebCore::OverlapMapContainer::ensureClippingScopeForLayers):
(WebCore::OverlapMapContainer::findClippingScopeForLayers const):
(WebCore::OverlapMapContainer::recursiveOutputToStream const):
(WebCore::OverlapMapContainer::dump const):
(WebCore::LayerOverlapMap::LayerOverlapMap):
(WebCore::LayerOverlapMap::add):
(WebCore::LayerOverlapMap::overlapsLayers const):
(WebCore::LayerOverlapMap::pushCompositingContainer):
(WebCore::LayerOverlapMap::popCompositingContainer):
(WebCore::OverlapMapContainer::unite): Deleted.
(WebCore::OverlapMapContainer::rectList const): Deleted.
* rendering/LayerOverlapMap.h:
* rendering/RenderLayerCompositor.cpp:
(WebCore::RenderLayerCompositor::BackingSharingState::appendSharingLayer):
(WebCore::RenderLayerCompositor::BackingSharingState::updateBeforeDescendantTraversal):
(WebCore::RenderLayerCompositor::updateCompositingLayers):
(WebCore::RenderLayerCompositor::computeCompositingRequirements):
(WebCore::RenderLayerCompositor::traverseUnchangedSubtree):
(WebCore::RenderLayerCompositor::computeExtent const):
(WebCore::createsClippingScope):
(WebCore::enclosingClippingScopes):
(WebCore::RenderLayerCompositor::addToOverlapMap const):
(WebCore::RenderLayerCompositor::updateOverlapMap const):
(WebCore::RenderLayerCompositor::layerOverlaps const):
* rendering/RenderLayerCompositor.h:

Source/WebCore/../../LayoutTests:

* TestExpectations:
* compositing/layer-creation/clipping-scope/nested-scroller-overlap-expected.txt: Added.
* compositing/layer-creation/clipping-scope/nested-scroller-overlap.html: Added.
* compositing/layer-creation/clipping-scope/overlap-constrained-inside-scroller-expected.txt: Added.
* compositing/layer-creation/clipping-scope/overlap-constrained-inside-scroller.html: Added.
* compositing/layer-creation/clipping-scope/overlap-constrained-inside-stacking-context-scroller-expected.txt: Added.
* compositing/layer-creation/clipping-scope/overlap-constrained-inside-stacking-context-scroller.html: Added.
* compositing/layer-creation/clipping-scope/scroller-with-negative-z-children-expected.txt: Added.
* compositing/layer-creation/clipping-scope/scroller-with-negative-z-children.html: Added.
* compositing/layer-creation/clipping-scope/shared-layers-in-scroller-expected.txt: Added.
* compositing/layer-creation/clipping-scope/shared-layers-in-scroller.html: Added.
* platform/ios-wk2/TestExpectations:
* platform/ios-wk2/compositing/layer-creation/clipping-scope/nested-scroller-overlap-expected.txt: Added.
* platform/ios-wk2/compositing/layer-creation/clipping-scope/overlap-constrained-inside-scroller-expected.txt: Added.
* platform/ios-wk2/compositing/layer-creation/clipping-scope/overlap-constrained-inside-stacking-context-scroller-expected.txt: Added.
* platform/ios-wk2/compositing/layer-creation/clipping-scope/scroller-with-negative-z-children-expected.txt: Added.
* platform/ios-wk2/compositing/layer-creation/clipping-scope/shared-layers-in-scroller-expected.txt: Added.
* platform/mac-wk2/TestExpectations:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@245602 268f45cc-cd09-0410-ab3c-d52691b4dbfc