Attachment 370447 Details for Bug 198139 – Patch

[patch] Patch

bug-198139-20190522145018.patch (text/plain), 22.27 KB, created by Simon Fraser (smfr) on 2019-05-22 14:50:19 PDT

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Creator: Simon Fraser (smfr)

Created: 2019-05-22 14:50:19 PDT

Size: 22.27 KB

patch

obsolete

>Subversion Revision: 245606
>diff --git a/Source/WebCore/ChangeLog b/Source/WebCore/ChangeLog
>index 44cc704186752bc1401f71c8d00419ef0168ca51..fa927863522a543b2540c954df2fc114144006f9 100644
>--- a/Source/WebCore/ChangeLog
>+++ b/Source/WebCore/ChangeLog
>@@ -1,3 +1,36 @@
>+2019-05-22  Simon Fraser  <simon.fraser@apple.com>
>+
>+        Fix scrolling tree state for more obscure combinations of positioning and paint order
>+        https://bugs.webkit.org/show_bug.cgi?id=198139
>+
>+        Reviewed by NOBODY (OOPS!).
>+
>+        There were three places in RenderLayerCompositor that used a version of ancestor
>+        layer traversal looking at containing blocks, and all three had issues. So make a
>+        shared function to do the ancestor walk, and use it thrice.
>+
>+        isScrolledByOverflowScrollLayer() fumbled containingBlockCanSkipLayers, so failed
>+        to create a scrolling tree node for a composited layer inside position:fixed in
>+        overflow (tested by composited-in-absolute-in-overflow.html).
>+
>+        collectStationaryLayerRelatedOverflowNodes() failed to handle nested
>+        overflow:scroll; it needs to find all the composited scrollers that affect the
>+        position of the given layer relative to its compositing ancestor, which may be the
>+        scroller, or a descendant of the scroller. However, it didn't walk up far enough
>+        and find more that one ancestor. Tested by absolute-in-nested-sc-scrollers.html.
>+
>+        enclosingClippingScopes() was OK but now uses the share function.
>+
>+        Tests: scrollingcoordinator/scrolling-tree/absolute-in-nested-sc-scrollers.html
>+               scrollingcoordinator/scrolling-tree/composited-in-absolute-in-overflow.html
>+
>+        * rendering/RenderLayerCompositor.cpp:
>+        (WebCore::traverseAncestorLayers):
>+        (WebCore::enclosingClippingScopes):
>+        (WebCore::isScrolledByOverflowScrollLayer):
>+        (WebCore::collectStationaryLayerRelatedOverflowNodes):
>+        (WebCore::collectRelatedCoordinatedScrollingNodes):
>+
> 2019-05-22  Simon Fraser  <simon.fraser@apple.com>
> 
>         Inner scroller of nested overflow:scrolls jitters when scrolling
>diff --git a/Source/WebCore/rendering/RenderLayerCompositor.cpp b/Source/WebCore/rendering/RenderLayerCompositor.cpp
>index 51c0d3a0141f2fe28fe666a9ebd1ed01b5c9e048..11e43eb25b68db802d9bf318bb77d3a87d9621a2 100644
>--- a/Source/WebCore/rendering/RenderLayerCompositor.cpp
>+++ b/Source/WebCore/rendering/RenderLayerCompositor.cpp
>@@ -1794,6 +1794,33 @@ void RenderLayerCompositor::computeExtent(const LayerOverlapMap& overlapMap, con
>     extent.extentComputed = true;
> }
> 
>+enum class AncestorTraversal { Continue, Stop };
>+
>+// This is a simplified version of containing block walking that only handles absolute position.
>+static AncestorTraversal traverseAncestorLayers(const RenderLayer& layer, const WTF::Function<AncestorTraversal(const RenderLayer&, bool inContainingBlockChain, bool isPaintOrderAncestor)>& ancestorFunc)
>+{
>+    bool containingBlockCanSkipLayers = layer.renderer().isAbsolutelyPositioned();
>+    RenderLayer* nextPaintOrderParent = layer.paintOrderParent();
>+
>+    for (const auto* ancestorLayer = layer.parent(); ancestorLayer; ancestorLayer = ancestorLayer->parent()) {
>+        bool inContainingBlockChain = true;
>+
>+        if (containingBlockCanSkipLayers)
>+            inContainingBlockChain = ancestorLayer->renderer().canContainAbsolutelyPositionedObjects();
>+
>+        if (ancestorFunc(*ancestorLayer, inContainingBlockChain, ancestorLayer == nextPaintOrderParent) == AncestorTraversal::Stop)
>+            return AncestorTraversal::Stop;
>+
>+        if (inContainingBlockChain)
>+            containingBlockCanSkipLayers = ancestorLayer->renderer().isAbsolutelyPositioned();
>+        
>+        if (ancestorLayer == nextPaintOrderParent)
>+            nextPaintOrderParent = ancestorLayer->paintOrderParent();
>+    }
>+    
>+    return AncestorTraversal::Continue;
>+}
>+
> static bool createsClippingScope(const RenderLayer& layer)
> {
>     return layer.hasCompositedScrollableOverflow();
>@@ -1807,27 +1834,20 @@ static Vector<LayerOverlapMap::LayerAndBounds> enclosingClippingScopes(const Ren
>     if (!layer.hasCompositedScrollingAncestor())
>         return clippingScopes;
> 
>-    bool containingBlockCanSkipLayers = layer.renderer().isAbsolutelyPositioned();
>-    for (const auto* ancestorLayer = layer.parent(); ancestorLayer; ancestorLayer = ancestorLayer->parent()) {
>-        bool inContainingBlockChain = true;
>-        if (containingBlockCanSkipLayers) {
>-            inContainingBlockChain = ancestorLayer->renderer().canContainAbsolutelyPositionedObjects();
>-            if (inContainingBlockChain)
>-                containingBlockCanSkipLayers = ancestorLayer->renderer().isAbsolutelyPositioned();
>-        }
>-        
>-        if (inContainingBlockChain && createsClippingScope(*ancestorLayer)) {
>+    traverseAncestorLayers(layer, [&](const RenderLayer& ancestorLayer, bool inContainingBlockChain, bool) {
>+        if (inContainingBlockChain && createsClippingScope(ancestorLayer)) {
>             LayoutRect clipRect;
>-            if (is<RenderBox>(ancestorLayer->renderer())) {
>+            if (is<RenderBox>(ancestorLayer.renderer())) {
>                 // FIXME: This is expensive. Broken with transforms.
>-                LayoutPoint offsetFromRoot = ancestorLayer->convertToLayerCoords(&rootLayer, { });
>-                clipRect = downcast<RenderBox>(ancestorLayer->renderer()).overflowClipRect(offsetFromRoot);
>+                LayoutPoint offsetFromRoot = ancestorLayer.convertToLayerCoords(&rootLayer, { });
>+                clipRect = downcast<RenderBox>(ancestorLayer.renderer()).overflowClipRect(offsetFromRoot);
>             }
> 
>-            LayerOverlapMap::LayerAndBounds layerAndBounds { const_cast<RenderLayer&>(*ancestorLayer), clipRect };
>+            LayerOverlapMap::LayerAndBounds layerAndBounds { const_cast<RenderLayer&>(ancestorLayer), clipRect };
>             clippingScopes.insert(1, layerAndBounds); // Order is roots to leaves.
>         }
>-    }
>+        return AncestorTraversal::Continue;
>+    });
> 
>     return clippingScopes;
> }
>@@ -3040,24 +3060,17 @@ static RenderLayer* enclosingCompositedScrollingLayer(const RenderLayer& layer,
>     return nullptr;
> }
> 
>-// Return true if overflowScrollLayer is in layer's containing block chain.
> static bool isScrolledByOverflowScrollLayer(const RenderLayer& layer, const RenderLayer& overflowScrollLayer)
> {
>-    bool containingBlockCanSkipLayers = layer.renderer().isAbsolutelyPositioned();
>-
>-    for (const auto* currLayer = layer.parent(); currLayer; currLayer = currLayer->parent()) {
>-        bool inContainingBlockChain = true;
>-        if (containingBlockCanSkipLayers) {
>-            inContainingBlockChain = currLayer->renderer().canContainAbsolutelyPositionedObjects();
>-            if (inContainingBlockChain)
>-                containingBlockCanSkipLayers = currLayer->renderer().isAbsolutelyPositioned();
>+    bool scrolledByOverflowScroll = false;
>+    traverseAncestorLayers(layer, [&](const RenderLayer& ancestorLayer, bool inContainingBlockChain, bool) {
>+        if (&ancestorLayer == &overflowScrollLayer) {
>+            scrolledByOverflowScroll = inContainingBlockChain;
>+            return AncestorTraversal::Stop;
>         }
>-
>-        if (currLayer == &overflowScrollLayer)
>-            return inContainingBlockChain;
>-    }
>-
>-    return false;
>+        return AncestorTraversal::Continue;
>+    });
>+    return scrolledByOverflowScroll;
> }
> 
> static bool isNonScrolledLayerInsideScrolledCompositedAncestor(const RenderLayer& layer, const RenderLayer& compositedAncestor, const RenderLayer& scrollingAncestor)
>@@ -3083,7 +3096,7 @@ bool RenderLayerCompositor::layerContainingBlockCrossesCoordinatedScrollingBound
>     return isNonScrolledLayerInsideScrolledCompositedAncestor(layer, compositedAncestor, *scrollingAncestor);
> }
> 
>-static void collectStationaryLayerRelatedOverflowNodes(const RenderLayer& layer, const RenderLayer& /*compositedAncestor*/, Vector<ScrollingNodeID>& scrollingNodes)
>+static void collectStationaryLayerRelatedOverflowNodes(const RenderLayer& layer, const RenderLayer&, Vector<ScrollingNodeID>& scrollingNodes)
> {
>     ASSERT(layer.isComposited());
>     
>@@ -3097,23 +3110,20 @@ static void collectStationaryLayerRelatedOverflowNodes(const RenderLayer& layer,
>     };
> 
>     ASSERT(layer.renderer().isAbsolutelyPositioned());
>-    bool containingBlockCanSkipLayers = true;
> 
>-    for (const auto* currLayer = layer.parent(); currLayer; currLayer = currLayer->parent()) {
>-        bool inContainingBlockChain = true;
>-        if (containingBlockCanSkipLayers) {
>-            inContainingBlockChain = currLayer->renderer().canContainAbsolutelyPositionedObjects();
>-            if (inContainingBlockChain)
>-                containingBlockCanSkipLayers = currLayer->renderer().isAbsolutelyPositioned();
>-        }
>+    // Collect all the composited scrollers which affect the position of this layer relative to its compositing ancestor (which might be inside the scroller or the scroller itself).
>+    bool seenPaintOrderAncestor = false;
>+    traverseAncestorLayers(layer, [&](const RenderLayer& ancestorLayer, bool isContainingBlockChain, bool isPaintOrderAncestor) {
>+        seenPaintOrderAncestor |= isPaintOrderAncestor;
>+        if (isContainingBlockChain && isPaintOrderAncestor)
>+            return AncestorTraversal::Stop;
> 
>-        if (currLayer->hasCompositedScrollableOverflow()) {
>-            appendOverflowLayerNodeID(*currLayer);
>-            break;
>-        }
>-    }
>-}
>+        if (seenPaintOrderAncestor && !isContainingBlockChain && ancestorLayer.hasCompositedScrollableOverflow())
>+            appendOverflowLayerNodeID(ancestorLayer);
> 
>+        return AncestorTraversal::Continue;
>+    });
>+}
> 
> ScrollPositioningBehavior RenderLayerCompositor::computeCoordinatedPositioningForLayer(const RenderLayer& layer) const
> {
>@@ -3182,7 +3192,6 @@ static Vector<ScrollingNodeID> collectRelatedCoordinatedScrollingNodes(const Ren
>     }
>     case ScrollPositioningBehavior::Stationary: {
>         ASSERT(layer.renderer().isAbsolutelyPositioned());
>-        // Collect all the composited scrollers between this layer and its composited ancestor.
>         auto* compositedAncestor = layer.ancestorCompositingLayer();
>         if (!compositedAncestor)
>             return overflowNodeData;
>diff --git a/LayoutTests/ChangeLog b/LayoutTests/ChangeLog
>index 93ab50707f5bfaf61aaffd7078b8c729c061dde1..d8c08ddb1bdc20c6a149b955c16f0aaa54f3269d 100644
>--- a/LayoutTests/ChangeLog
>+++ b/LayoutTests/ChangeLog
>@@ -1,3 +1,17 @@
>+2019-05-22  Simon Fraser  <simon.fraser@apple.com>
>+
>+        Fix scrolling tree state for more obscure combinations of positioning and paint order
>+        https://bugs.webkit.org/show_bug.cgi?id=198139
>+
>+        Reviewed by NOBODY (OOPS!).
>+
>+        * platform/ios-wk2/scrollingcoordinator/scrolling-tree/absolute-in-nested-sc-scrollers-expected.txt: Added.
>+        * platform/ios-wk2/scrollingcoordinator/scrolling-tree/composited-in-absolute-in-overflow-expected.txt: Added.
>+        * scrollingcoordinator/scrolling-tree/absolute-in-nested-sc-scrollers-expected.txt: Added.
>+        * scrollingcoordinator/scrolling-tree/absolute-in-nested-sc-scrollers.html: Added.
>+        * scrollingcoordinator/scrolling-tree/composited-in-absolute-in-overflow-expected.txt: Added.
>+        * scrollingcoordinator/scrolling-tree/composited-in-absolute-in-overflow.html: Added.
>+
> 2019-05-22  Simon Fraser  <simon.fraser@apple.com>
> 
>         Inner scroller of nested overflow:scrolls jitters when scrolling
>diff --git a/LayoutTests/platform/ios-wk2/scrollingcoordinator/scrolling-tree/absolute-in-nested-sc-scrollers-expected.txt b/LayoutTests/platform/ios-wk2/scrollingcoordinator/scrolling-tree/absolute-in-nested-sc-scrollers-expected.txt
>new file mode 100644
>index 0000000000000000000000000000000000000000..33045c310fa7d5222f0aee94ec4a597c631504b3
>--- /dev/null
>+++ b/LayoutTests/platform/ios-wk2/scrollingcoordinator/scrolling-tree/absolute-in-nested-sc-scrollers-expected.txt
>@@ -0,0 +1,50 @@
>+
>+(Frame scrolling node
>+  (scrollable area size 800 600)
>+  (contents size 800 600)
>+  (parent relative scrollable rect at (0,0) size 800x600)
>+  (scrollable area parameters 
>+    (horizontal scroll elasticity 1)
>+    (vertical scroll elasticity 1)
>+    (horizontal scrollbar mode 0)
>+    (vertical scrollbar mode 0))
>+  (layout viewport at (0,0) size 800x600)
>+  (min layout viewport origin (0,0))
>+  (max layout viewport origin (0,0))
>+  (behavior for fixed 0)
>+  (children 1
>+    (Overflow scrolling node
>+      (scrollable area size 300 300)
>+      (contents size 300 794)
>+      (parent relative scrollable rect at (30,22) size 300x300)
>+      (scrollable area parameters 
>+        (horizontal scroll elasticity 1)
>+        (vertical scroll elasticity 1)
>+        (horizontal scrollbar mode 0)
>+        (vertical scrollbar mode 0)
>+        (has enabled vertical scrollbar 1))
>+      (children 1
>+        (Overflow scrolling node
>+          (scrollable area size 250 250)
>+          (contents size 250 500)
>+          (parent relative scrollable rect at (24,24) size 250x250)
>+          (scrollable area parameters 
>+            (horizontal scroll elasticity 1)
>+            (vertical scroll elasticity 1)
>+            (horizontal scrollbar mode 0)
>+            (vertical scrollbar mode 0)
>+            (has enabled vertical scrollbar 1))
>+          (children 1
>+            (Positioned node
>+              (layout constraints 
>+                (layer-position-at-last-layout (-2,6))
>+                (positioning-behavior stationary))
>+              (related overflow nodes 2)
>+            )
>+          )
>+        )
>+      )
>+    )
>+  )
>+)
>+
>diff --git a/LayoutTests/platform/ios-wk2/scrollingcoordinator/scrolling-tree/composited-in-absolute-in-overflow-expected.txt b/LayoutTests/platform/ios-wk2/scrollingcoordinator/scrolling-tree/composited-in-absolute-in-overflow-expected.txt
>new file mode 100644
>index 0000000000000000000000000000000000000000..3349b35b836daf5949525527e9f9ed3fece28beb
>--- /dev/null
>+++ b/LayoutTests/platform/ios-wk2/scrollingcoordinator/scrolling-tree/composited-in-absolute-in-overflow-expected.txt
>@@ -0,0 +1,29 @@
>+
>+(Frame scrolling node
>+  (scrollable area size 800 600)
>+  (contents size 800 600)
>+  (parent relative scrollable rect at (0,0) size 800x600)
>+  (scrollable area parameters 
>+    (horizontal scroll elasticity 1)
>+    (vertical scroll elasticity 1)
>+    (horizontal scrollbar mode 0)
>+    (vertical scrollbar mode 0))
>+  (layout viewport at (0,0) size 800x600)
>+  (min layout viewport origin (0,0))
>+  (max layout viewport origin (0,0))
>+  (behavior for fixed 0)
>+  (children 1
>+    (Overflow scrolling node
>+      (scrollable area size 300 300)
>+      (contents size 300 1000)
>+      (parent relative scrollable rect at (30,22) size 300x300)
>+      (scrollable area parameters 
>+        (horizontal scroll elasticity 1)
>+        (vertical scroll elasticity 1)
>+        (horizontal scrollbar mode 0)
>+        (vertical scrollbar mode 0)
>+        (has enabled vertical scrollbar 1))
>+    )
>+  )
>+)
>+
>diff --git a/LayoutTests/scrollingcoordinator/scrolling-tree/absolute-in-nested-sc-scrollers-expected.txt b/LayoutTests/scrollingcoordinator/scrolling-tree/absolute-in-nested-sc-scrollers-expected.txt
>new file mode 100644
>index 0000000000000000000000000000000000000000..86b8d927b4b71ed3abbcce2ceefa18cbe506ba16
>--- /dev/null
>+++ b/LayoutTests/scrollingcoordinator/scrolling-tree/absolute-in-nested-sc-scrollers-expected.txt
>@@ -0,0 +1,50 @@
>+
>+(Frame scrolling node
>+  (scrollable area size 800 600)
>+  (contents size 800 600)
>+  (parent relative scrollable rect at (0,0) size 800x600)
>+  (scrollable area parameters 
>+    (horizontal scroll elasticity 2)
>+    (vertical scroll elasticity 2)
>+    (horizontal scrollbar mode 0)
>+    (vertical scrollbar mode 0))
>+  (layout viewport at (0,0) size 800x600)
>+  (min layout viewport origin (0,0))
>+  (max layout viewport origin (0,0))
>+  (behavior for fixed 0)
>+  (children 1
>+    (Overflow scrolling node
>+      (scrollable area size 285 285)
>+      (contents size 285 794)
>+      (parent relative scrollable rect at (30,22) size 285x285)
>+      (scrollable area parameters 
>+        (horizontal scroll elasticity 0)
>+        (vertical scroll elasticity 0)
>+        (horizontal scrollbar mode 0)
>+        (vertical scrollbar mode 0)
>+        (has enabled vertical scrollbar 1))
>+      (children 1
>+        (Overflow scrolling node
>+          (scrollable area size 235 235)
>+          (contents size 235 500)
>+          (parent relative scrollable rect at (24,24) size 235x235)
>+          (scrollable area parameters 
>+            (horizontal scroll elasticity 0)
>+            (vertical scroll elasticity 0)
>+            (horizontal scrollbar mode 0)
>+            (vertical scrollbar mode 0)
>+            (has enabled vertical scrollbar 1))
>+          (children 1
>+            (Positioned node
>+              (layout constraints 
>+                (layer-position-at-last-layout (-2,6))
>+                (positioning-behavior stationary))
>+              (related overflow nodes 2)
>+            )
>+          )
>+        )
>+      )
>+    )
>+  )
>+)
>+
>diff --git a/LayoutTests/scrollingcoordinator/scrolling-tree/absolute-in-nested-sc-scrollers.html b/LayoutTests/scrollingcoordinator/scrolling-tree/absolute-in-nested-sc-scrollers.html
>new file mode 100644
>index 0000000000000000000000000000000000000000..a62637c53ccea2bed8b2a2ce6b273147ea1e771d
>--- /dev/null
>+++ b/LayoutTests/scrollingcoordinator/scrolling-tree/absolute-in-nested-sc-scrollers.html
>@@ -0,0 +1,68 @@
>+<!DOCTYPE html> 
>+<html>
>+<head>
>+    <title>Tests that we make a scrolling tree node for composited layers nested inside position:absolute in a scroller</title>
>+    <style>
>+        .scroller {
>+            overflow: scroll;
>+            margin: 20px;
>+            height: 300px;
>+            width: 300px;
>+            border: 2px solid black;
>+            opacity: 0.8;
>+        }
>+
>+        .scroller > .scroller {
>+            height: 250px;
>+            width: 250px;
>+        }
>+
>+        .absolute {
>+            position:absolute;
>+            left: 50px;
>+            top: 50px;
>+            width: 200px;
>+            height: 120px;
>+            padding: 20px;
>+            background: gray;
>+        }
>+        
>+        .composited {
>+            transform: translateZ(0);
>+        }
>+        
>+        .box {
>+            width: 100px;
>+            height: 100px;
>+            background-color: green;
>+        }
>+        
>+        .spacer {
>+            height: 500px;
>+            width: 20px;
>+            background-color: silver;
>+        }
>+    </style>
>+    <script>
>+        if (window.testRunner)
>+            testRunner.dumpAsText();
>+
>+        window.addEventListener('load', () => {
>+            if (window.internals)
>+                document.getElementById('tree').innerText = internals.scrollingStateTreeAsText();
>+        }, false);
>+    </script>
>+</head>
>+<body>
>+    <div class="scroller">
>+        <div class="scroller">
>+            <div class="absolute">
>+                
>+            </div>
>+            <div class="spacer"></div>
>+        </div>
>+        <div class="spacer"></div>
>+    </div>
>+<pre id="tree"></pre>
>+</body>
>+</html>
>diff --git a/LayoutTests/scrollingcoordinator/scrolling-tree/composited-in-absolute-in-overflow-expected.txt b/LayoutTests/scrollingcoordinator/scrolling-tree/composited-in-absolute-in-overflow-expected.txt
>new file mode 100644
>index 0000000000000000000000000000000000000000..9c8b4d2e662aa2b3bbf07a1d8e76e14f6c730530
>--- /dev/null
>+++ b/LayoutTests/scrollingcoordinator/scrolling-tree/composited-in-absolute-in-overflow-expected.txt
>@@ -0,0 +1,29 @@
>+
>+(Frame scrolling node
>+  (scrollable area size 800 600)
>+  (contents size 800 600)
>+  (parent relative scrollable rect at (0,0) size 800x600)
>+  (scrollable area parameters 
>+    (horizontal scroll elasticity 2)
>+    (vertical scroll elasticity 2)
>+    (horizontal scrollbar mode 0)
>+    (vertical scrollbar mode 0))
>+  (layout viewport at (0,0) size 800x600)
>+  (min layout viewport origin (0,0))
>+  (max layout viewport origin (0,0))
>+  (behavior for fixed 0)
>+  (children 1
>+    (Overflow scrolling node
>+      (scrollable area size 285 285)
>+      (contents size 285 1000)
>+      (parent relative scrollable rect at (30,22) size 285x285)
>+      (scrollable area parameters 
>+        (horizontal scroll elasticity 0)
>+        (vertical scroll elasticity 0)
>+        (horizontal scrollbar mode 0)
>+        (vertical scrollbar mode 0)
>+        (has enabled vertical scrollbar 1))
>+    )
>+  )
>+)
>+
>diff --git a/LayoutTests/scrollingcoordinator/scrolling-tree/composited-in-absolute-in-overflow.html b/LayoutTests/scrollingcoordinator/scrolling-tree/composited-in-absolute-in-overflow.html
>new file mode 100644
>index 0000000000000000000000000000000000000000..7c45a982ffbd04be83322d80b67a6470b817ca87
>--- /dev/null
>+++ b/LayoutTests/scrollingcoordinator/scrolling-tree/composited-in-absolute-in-overflow.html
>@@ -0,0 +1,58 @@
>+<!DOCTYPE html> 
>+<html>
>+<head>
>+    <title>Tests that we make a scrolling tree node for composited layers nested inside position:absolute in a scroller</title>
>+    <style>
>+        .scroller {
>+            overflow: scroll;
>+            margin: 20px;
>+            height: 300px;
>+            width: 300px;
>+            border: 2px solid black;
>+        }
>+
>+        .absolute {
>+            position:absolute;
>+            left: 50px;
>+            top: 50px;
>+            width: 200px;
>+            height: 120px;
>+            padding: 20px;
>+            background: gray;
>+        }
>+        
>+        .composited {
>+            transform: translateZ(0);
>+        }
>+        
>+        .box {
>+            width: 100px;
>+            height: 100px;
>+            background-color: green;
>+        }
>+        
>+        .spacer {
>+            height: 500px;
>+        }
>+    </style>
>+    <script>
>+        if (window.testRunner)
>+            testRunner.dumpAsText();
>+
>+        window.addEventListener('load', () => {
>+            if (window.internals)
>+                document.getElementById('tree').innerText = internals.scrollingStateTreeAsText();
>+        }, false);
>+    </script>
>+</head>
>+<body>
>+    <div class="scroller">
>+        <div class="spacer"></div>
>+        <div class="absolute">
>+            <div class="composited box"></div>
>+        </div>
>+        <div class="spacer"></div>
>+    </div>
>+<pre id="tree"></pre>
>+</body>
>+</html>

Flags:

koivisto: review+

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Attachments on bug 198139: 370447