tree c8758c247e61a2f21d043cdf957a4006715cad41
parent 2e01d18091ad946a40770a39cb3dadc0fabeb062
author simon.fraser@apple.com <simon.fraser@apple.com@268f45cc-cd09-0410-ab3c-d52691b4dbfc> 1557336112 +0000
committer simon.fraser@apple.com <simon.fraser@apple.com@268f45cc-cd09-0410-ab3c-d52691b4dbfc> 1557336112 +0000

Implement backing-sharing in compositing layers, allowing overlap layers to paint into the backing store of another layer
https://bugs.webkit.org/show_bug.cgi?id=197561
<rdar://problem/50445998>

Reviewed by Antti Koivisto.
Source/WebCore:

This change introduces the concept of layers that share backing store for compositing. A layer
which is sharing its backing store first paints itself, and then some set of layers which come
later in paint order in the same stacking context. This reduces the composited layer count in
some overflow scrolling scenarios, thereby also simplifying the scrolling tree.

A backing-shared layer stores a vector of "sharing" RenderLayer* in its RenderLayerBacking. At
paint time, the owning layer is painted, then the sharing layers, setting the owning layer as the
painting root so that positioning and clipping just work.

Sharing layer relationships are constructed in RenderLayerCompositor::computeCompositingRequirements().
We track the last layer which was composited in paint order as a shared candidate. If a later layer
would composite for overlap (and no other reasons), then we allow it to share with the candidate
if the candidate is in its ancestor containing block chain. Sharing is currently limited to layers
in the same stacking context.

isComposited() returns false for sharing layers, but they are like composited layers in that
they behave as painting boundaries, so RenderLayer::paintLayer() needs to stop at them,
and repaints in shared layers have to be directed to their shared layer, hence
changes to RenderLayer::clippingRootForPainting() and RenderLayer::enclosingCompositingLayerForRepaint().

The clipping boundary logic in RenderLayer::backgroundClipRect() needed to be generalized so that
all calls to RenderLayer::parentClipRects() check for crossing painting boundaries and use
TemporaryClipRects in that case.

Tests: compositing/shared-backing/overflow-scroll/absolute-in-stacking-relative-in-scroller.html
       compositing/shared-backing/overflow-scroll/composited-absolute-in-absolute-in-relative-in-scroller.html
       compositing/shared-backing/overflow-scroll/nested-absolute-with-clipping-in-stacking-overflow.html
       compositing/shared-backing/overflow-scroll/previous-sibling-prevents-inclusiveness.html
       compositing/shared-backing/overflow-scroll/relative-in-clipping-in-scroller-in-clipping.html
       compositing/shared-backing/overflow-scroll/relative-in-clipping-in-scroller-in-relative-clipping.html
       compositing/shared-backing/overflow-scroll/relative-in-div-in-overflow-scroll.html
       compositing/shared-backing/overflow-scroll/scrolled-contents-has-painted-content.html
       compositing/shared-backing/overflow-scroll/scrolled-contents-unconstrained-clip.html
       compositing/shared-backing/overflow-scroll/shared-layer-clipping.html
       compositing/shared-backing/overflow-scroll/shared-layer-composited-bounds.html
       compositing/shared-backing/overflow-scroll/shared-layer-nested-relative-stacking.html
       compositing/shared-backing/overflow-scroll/shared-layer-repaint.html
       compositing/shared-backing/partial-compositing-update.html
       compositing/shared-backing/partial-compositing-update2.html
       compositing/shared-backing/remove-sharing-layer.html
       compositing/shared-backing/sharing-cached-clip-rects.html

* rendering/RenderLayer.cpp:
(WebCore::RenderLayer::~RenderLayer):
(WebCore::RenderLayer::ancestorLayerIsInContainingBlockChain const):
(WebCore::RenderLayer::setBackingProviderLayer):
(WebCore::RenderLayer::disconnectFromBackingProviderLayer):
(WebCore::RenderLayer::enclosingCompositingLayerForRepaint const):
(WebCore::RenderLayer::clippingRootForPainting const):
(WebCore::RenderLayer::clipToRect):
(WebCore::RenderLayer::paintLayer):
(WebCore::RenderLayer::updateClipRects):
(WebCore::RenderLayer::clipCrossesPaintingBoundary const):
(WebCore::RenderLayer::calculateClipRects const):
(WebCore::outputPaintOrderTreeLegend):
(WebCore::outputPaintOrderTreeRecursive):
(WebCore::inContainingBlockChain): Deleted.
* rendering/RenderLayer.h:
* rendering/RenderLayerBacking.cpp:
(WebCore::RenderLayerBacking::willBeDestroyed):
(WebCore::clearBackingSharingLayerProviders):
(WebCore::RenderLayerBacking::setBackingSharingLayers):
(WebCore::RenderLayerBacking::removeBackingSharingLayer):
(WebCore::RenderLayerBacking::clearBackingSharingLayers):
(WebCore::RenderLayerBacking::updateCompositedBounds):
(WebCore::RenderLayerBacking::updateDrawsContent):
(WebCore::RenderLayerBacking::isSimpleContainerCompositingLayer const):
(WebCore::RenderLayerBacking::paintIntoLayer):
(WebCore::RenderLayerBacking::paintContents):
* rendering/RenderLayerBacking.h:
* rendering/RenderLayerCompositor.cpp:
(WebCore::RenderLayerCompositor::CompositingState::stateForPaintOrderChildren const):
(WebCore::RenderLayerCompositor::CompositingState::propagateStateFromChildren):
(WebCore::RenderLayerCompositor::CompositingState::propagateStateFromChildrenForUnchangedSubtree):
(WebCore::RenderLayerCompositor::BackingSharingState::resetBackingProviderCandidate):
(WebCore::RenderLayerCompositor::updateCompositingLayers):
(WebCore::backingProviderLayerCanIncludeLayer):
(WebCore::RenderLayerCompositor::computeCompositingRequirements):
(WebCore::RenderLayerCompositor::traverseUnchangedSubtree):
(WebCore::RenderLayerCompositor::updateBacking):
(WebCore::RenderLayerCompositor::layerWillBeRemoved):
(WebCore::RenderLayerCompositor::requiresCompositingForIndirectReason const):
* rendering/RenderLayerCompositor.h:
* rendering/RenderTreeAsText.cpp:

LayoutTests:

New tests for backing sharing, and new baselines of tests whose behavior is changed.

Scrolling tree tests that would be invalidate by sharing are changed to defeat sharing by adding
compositing layers early in stacking order.

* TestExpectations:
* compositing/geometry/limit-layer-bounds-clipping-ancestor-expected.txt:
* compositing/layer-creation/overflow-scroll-overlap-expected.txt:
* compositing/layer-creation/overflow-scroll-overlap.html:
* compositing/overflow/scrolling-content-clip-to-viewport.html:
* compositing/rtl/rtl-scrolling-with-transformed-descendants-expected.txt:
* compositing/shared-backing/overflow-scroll/absolute-in-stacking-relative-in-scroller-expected.txt: Copied from LayoutTests/platform/ios/compositing/overflow/scrolling-content-clip-to-viewport-expected.txt.
* compositing/shared-backing/overflow-scroll/absolute-in-stacking-relative-in-scroller.html: Added.
* compositing/shared-backing/overflow-scroll/composited-absolute-in-absolute-in-relative-in-scroller-expected.txt: Added.
* compositing/shared-backing/overflow-scroll/composited-absolute-in-absolute-in-relative-in-scroller.html: Added.
* compositing/shared-backing/overflow-scroll/nested-absolute-with-clipping-in-stacking-overflow-expected.txt: Added.
* compositing/shared-backing/overflow-scroll/nested-absolute-with-clipping-in-stacking-overflow.html: Copied from LayoutTests/scrollingcoordinator/scrolling-tree/nested-absolute-in-sc-overflow.html.
* compositing/shared-backing/overflow-scroll/previous-sibling-prevents-inclusiveness-expected.txt: Added.
* compositing/shared-backing/overflow-scroll/previous-sibling-prevents-inclusiveness.html: Added.
* compositing/shared-backing/overflow-scroll/relative-in-clipping-in-scroller-in-clipping-expected.txt: Added.
* compositing/shared-backing/overflow-scroll/relative-in-clipping-in-scroller-in-clipping.html: Added.
* compositing/shared-backing/overflow-scroll/relative-in-clipping-in-scroller-in-relative-clipping-expected.txt: Added.
* compositing/shared-backing/overflow-scroll/relative-in-clipping-in-scroller-in-relative-clipping.html: Added.
* compositing/shared-backing/overflow-scroll/relative-in-div-in-overflow-scroll-expected.txt: Copied from LayoutTests/platform/ios/compositing/overflow/scrolling-content-clip-to-viewport-expected.txt.
* compositing/shared-backing/overflow-scroll/relative-in-div-in-overflow-scroll.html: Added.
* compositing/shared-backing/overflow-scroll/scrolled-contents-has-painted-content-expected.txt: Copied from LayoutTests/platform/ios/compositing/overflow/scrolling-content-clip-to-viewport-expected.txt.
* compositing/shared-backing/overflow-scroll/scrolled-contents-has-painted-content.html: Added.
* compositing/shared-backing/overflow-scroll/scrolled-contents-unconstrained-clip-expected.html: Added.
* compositing/shared-backing/overflow-scroll/scrolled-contents-unconstrained-clip.html: Added.
* compositing/shared-backing/overflow-scroll/shared-layer-clipping-expected.html: Added.
* compositing/shared-backing/overflow-scroll/shared-layer-clipping.html: Added.
* compositing/shared-backing/overflow-scroll/shared-layer-composited-bounds-expected.txt: Added.
* compositing/shared-backing/overflow-scroll/shared-layer-composited-bounds.html: Added.
* compositing/shared-backing/overflow-scroll/shared-layer-nested-relative-stacking-expected.txt: Added.
* compositing/shared-backing/overflow-scroll/shared-layer-nested-relative-stacking.html: Added.
* compositing/shared-backing/overflow-scroll/shared-layer-repaint-expected.txt: Added.
* compositing/shared-backing/overflow-scroll/shared-layer-repaint.html: Added.
* compositing/shared-backing/partial-compositing-update-expected.txt: Added.
* compositing/shared-backing/partial-compositing-update.html: Added.
* compositing/shared-backing/partial-compositing-update2-expected.txt: Added.
* compositing/shared-backing/partial-compositing-update2.html: Added.
* compositing/shared-backing/remove-sharing-layer-expected.txt: Added.
* compositing/shared-backing/remove-sharing-layer.html: Added.
* compositing/shared-backing/sharing-cached-clip-rects-expected.txt: Added.
* compositing/shared-backing/sharing-cached-clip-rects.html: Added.
* platform/ios-wk2/TestExpectations:
* platform/ios-wk2/compositing/shared-backing/overflow-scroll/absolute-in-stacking-relative-in-scroller-expected.txt: Copied from LayoutTests/platform/ios/compositing/overflow/scrolling-content-clip-to-viewport-expected.txt.
* platform/ios-wk2/compositing/shared-backing/overflow-scroll/composited-absolute-in-absolute-in-relative-in-scroller-expected.txt: Added.
* platform/ios-wk2/compositing/shared-backing/overflow-scroll/nested-absolute-with-clipping-in-stacking-overflow-expected.txt: Added.
* platform/ios-wk2/compositing/shared-backing/overflow-scroll/previous-sibling-prevents-inclusiveness-expected.txt: Added.
* platform/ios-wk2/compositing/shared-backing/overflow-scroll/relative-in-clipping-in-scroller-in-clipping-expected.txt: Added.
* platform/ios-wk2/compositing/shared-backing/overflow-scroll/relative-in-clipping-in-scroller-in-relative-clipping-expected.txt: Added.
* platform/ios-wk2/compositing/shared-backing/overflow-scroll/relative-in-div-in-overflow-scroll-expected.txt: Copied from LayoutTests/platform/ios/compositing/overflow/scrolling-content-clip-to-viewport-expected.txt.
* platform/ios-wk2/compositing/shared-backing/overflow-scroll/scrolled-contents-has-painted-content-expected.txt: Copied from LayoutTests/platform/ios/compositing/overflow/scrolling-content-clip-to-viewport-expected.txt.
* platform/ios-wk2/scrollingcoordinator/scrolling-tree/nested-absolute-in-absolute-overflow-expected.txt:
* platform/ios-wk2/scrollingcoordinator/scrolling-tree/nested-absolute-in-relative-in-overflow-expected.txt:
* platform/ios-wk2/scrollingcoordinator/scrolling-tree/nested-absolute-in-sc-overflow-expected.txt:
* platform/ios-wk2/scrollingcoordinator/scrolling-tree/positioned-nodes-complex-expected.txt:
* platform/ios/compositing/geometry/limit-layer-bounds-clipping-ancestor-expected.txt:
* platform/ios/compositing/overflow/clipping-behaviour-change-is-not-propagated-to-descendants-expected.txt:
* platform/ios/compositing/overflow/clipping-behaviour-change-is-not-propagated-to-descendants2-expected.txt:
* platform/ios/compositing/overflow/scrolling-content-clip-to-viewport-expected.txt:
* platform/mac-wk1/compositing/overflow/scrolling-content-clip-to-viewport-expected.txt:
* platform/mac-wk2/TestExpectations:
* platform/mac/compositing/overflow/clipping-behaviour-change-is-not-propagated-to-descendants-expected.txt:
* platform/mac/compositing/overflow/clipping-behaviour-change-is-not-propagated-to-descendants2-expected.txt:
* scrollingcoordinator/scrolling-tree/nested-absolute-in-absolute-overflow-expected.txt:
* scrollingcoordinator/scrolling-tree/nested-absolute-in-absolute-overflow.html:
* scrollingcoordinator/scrolling-tree/nested-absolute-in-relative-in-overflow-expected.txt:
* scrollingcoordinator/scrolling-tree/nested-absolute-in-relative-in-overflow.html:
* scrollingcoordinator/scrolling-tree/nested-absolute-in-sc-overflow-expected.txt:
* scrollingcoordinator/scrolling-tree/nested-absolute-in-sc-overflow.html:
* scrollingcoordinator/scrolling-tree/positioned-nodes-complex-expected.txt:
* scrollingcoordinator/scrolling-tree/positioned-nodes-complex.html:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@245058 268f45cc-cd09-0410-ab3c-d52691b4dbfc