Overlay scrollbars must respect ancestor clip

Source/core/rendering/compositing/CompositedLayerMapping.cpp

 /*
  * Copyright (C) 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 169 matching lines @@
     // Do not leave the destroyed pointer dangling on any RenderLayers that painted to this mapping's squashing layer.
     for (size_t i = 0; i < m_squashedLayers.size(); ++i) {
         RenderLayer* oldSquashedLayer = m_squashedLayers[i].renderLayer;
         if (oldSquashedLayer->groupedMapping() == this) {
             oldSquashedLayer->setGroupedMapping(0, true);
             oldSquashedLayer->setLostGroupedMapping(true);
         }
     }
 
     updateClippingLayers(false, false);
-    updateOverflowControlsLayers(false, false, false);
+    updateOverflowControlsLayers(false, false, false, false);
     updateChildTransformLayer(false);
     updateForegroundLayer(false);
     updateBackgroundLayer(false);
     updateMaskLayer(false);
     updateClippingMaskLayers(false);
     updateScrollingLayers(false);
     updateSquashingLayers(false);
     destroyGraphicsLayers();
 }
 
@@ skipping 180 matching lines @@
     if (scrollParent) {
         // If our containing block is our ancestor scrolling layer, then we'll already be clipped
         // to it via our scroll parent and we don't need an ancestor clipping layer.
         if (m_owningLayer.renderer()->containingBlock()->enclosingLayer() == m_owningLayer.ancestorScrollingLayer())
             needsAncestorClip = false;
     }
 
     if (updateClippingLayers(needsAncestorClip, needsDescendantsClippingLayer))
         layerConfigChanged = true;
 
-    if (updateOverflowControlsLayers(requiresHorizontalScrollbarLayer(), requiresVerticalScrollbarLayer(), requiresScrollCornerLayer()))
+    if (updateOverflowControlsLayers(requiresHorizontalScrollbarLayer(), requiresVerticalScrollbarLayer(), requiresScrollCornerLayer(), needsAncestorClip))
         layerConfigChanged = true;
 
     bool scrollingConfigChanged = false;
     if (updateScrollingLayers(m_owningLayer.needsCompositedScrolling())) {
         layerConfigChanged = true;
         scrollingConfigChanged = true;
     }
 
     bool hasPerspective = false;
     if (RenderStyle* style = renderer->style())
@@ skipping 189 matching lines @@
     squashingLayer->setPosition(squashLayerBounds.location());
     squashingLayer->setSize(squashLayerBounds.size());
 
     *offsetFromTransformedAncestor = referenceOffsetFromTransformedAncestor;
     offsetFromTransformedAncestor->move(squashLayerOriginInOwningLayerSpace);
 
     for (size_t i = 0; i < layers.size(); ++i)
         layers[i].localClipRectForSquashedLayer = localClipRectForSquashedLayer(referenceLayer, layers[i], layers);
 }
 
-void CompositedLayerMapping::updateGraphicsLayerGeometry(const RenderLayer* compositingContainer, Vector<RenderLayer*>& layersNeedingPaintInvalidation)
+void CompositedLayerMapping::updateGraphicsLayerGeometry(const RenderLayer* compositingContainer, const RenderLayer* compositingStackingContext, Vector<RenderLayer*>& layersNeedingPaintInvalidation)
 {
     ASSERT(m_owningLayer.compositor()->lifecycle().state() == DocumentLifecycle::InCompositingUpdate);
 
     // Set transform property, if it is not animating. We have to do this here because the transform
     // is affected by the layer dimensions.
     if (!renderer()->style()->isRunningTransformAnimationOnCompositor())
         updateTransform(renderer()->style());
 
     // Set opacity, if it is not animating.
     if (!renderer()->style()->isRunningOpacityAnimationOnCompositor())
@@ skipping 13 matching lines @@
     IntRect relativeCompositingBounds;
     LayoutPoint offsetFromCompositedAncestor;
     IntPoint snappedOffsetFromCompositedAncestor;
     computeBoundsOfOwningLayer(compositingContainer, localCompositingBounds, relativeCompositingBounds, offsetFromCompositedAncestor, snappedOffsetFromCompositedAncestor);
 
     IntPoint graphicsLayerParentLocation;
     computeGraphicsLayerParentLocation(compositingContainer, ancestorCompositingBounds, graphicsLayerParentLocation);
 
     // Might update graphicsLayerParentLocation.
     updateAncestorClippingLayerGeometry(compositingContainer, snappedOffsetFromCompositedAncestor, graphicsLayerParentLocation);
+    updateOverflowControlsHostLayerGeometry(compositingStackingContext);
 
     FloatSize contentsSize = relativeCompositingBounds.size();
 
     updateMainGraphicsLayerGeometry(relativeCompositingBounds, localCompositingBounds, graphicsLayerParentLocation);
     updateSquashingLayerGeometry(offsetFromCompositedAncestor, graphicsLayerParentLocation, m_owningLayer, m_squashedLayers, m_squashingLayer.get(), &m_squashingLayerOffsetFromTransformedAncestor, layersNeedingPaintInvalidation);
 
     // If we have a layer that clips children, position it.
     IntRect clippingBox;
     if (m_childContainmentLayer)
         clippingBox = clipBox(toRenderBox(renderer()));
@@ skipping 94 matching lines @@
     m_ancestorClippingLayer->setPosition(FloatPoint(parentClipRect.location() - graphicsLayerParentLocation));
     m_ancestorClippingLayer->setSize(parentClipRect.size());
 
     // backgroundRect is relative to compositingContainer, so subtract snappedOffsetFromCompositedAncestor.X/snappedOffsetFromCompositedAncestor.Y to get back to local coords.
     m_ancestorClippingLayer->setOffsetFromRenderer(parentClipRect.location() - snappedOffsetFromCompositedAncestor);
 
     // The primary layer is then parented in, and positioned relative to this clipping layer.
     graphicsLayerParentLocation = parentClipRect.location();
 }
 
+static FloatPoint relativePositionInTransformedAncestorSpace(const RenderLayer* layer, const RenderLayer* compositingStackingContext)

[hartmanng, 2014/07/24 15:57:35]

I find this name a bit confusing. When I read it, I assume this function will
basically be returning the value you call 'localOffsetToTransformedAncestor'.
But maybe that's just me?

My best suggestion is something like
offsetFromCompositingStackingContextInTransformedAncestorSpace, but that's
getting pretty verbose.

[Ian Vollick, 2014/07/24 17:39:09]

Yeah, the name's crappy. I've sidestepped the issue by inlining this function.
It's not used anywhere else.

+{
+    ASSERT(layer->transformAncestor() == compositingStackingContext->transformAncestor());
+    LayoutPoint localOffsetToTransformedAncestor = layer->computeOffsetFromTransformedAncestor();
+    LayoutPoint compositingStackingContextOffsetToTransformedAncestor = compositingStackingContext->computeOffsetFromTransformedAncestor();
+    return FloatPoint(localOffsetToTransformedAncestor - compositingStackingContextOffsetToTransformedAncestor);
+}
+
+void CompositedLayerMapping::updateOverflowControlsHostLayerGeometry(const RenderLayer* compositingStackingContext)
+{
+    if (!m_overflowControlsHostLayer)
+        return;
+
+    if (m_owningLayer.needsToReparentOverflowControls()) {
+        if (m_overflowControlsClippingLayer) {
+            m_overflowControlsClippingLayer->setPosition(m_ancestorClippingLayer->position());
+            m_overflowControlsClippingLayer->setSize(m_ancestorClippingLayer->size());
+            m_overflowControlsClippingLayer->setOffsetFromRenderer(m_ancestorClippingLayer->offsetFromRenderer());
+            m_overflowControlsClippingLayer->setMasksToBounds(true);
+
+            m_overflowControlsHostLayer->setPosition(IntPoint(-m_overflowControlsClippingLayer->offsetFromRenderer()));
+        } else {
+            m_overflowControlsHostLayer->setPosition(relativePositionInTransformedAncestorSpace(&m_owningLayer, compositingStackingContext));
+        }
+    } else {
+        m_overflowControlsHostLayer->setPosition(FloatPoint());
+    }
+}
+
 void CompositedLayerMapping::updateChildContainmentLayerGeometry(const IntRect& clippingBox, const IntRect& localCompositingBounds)
 {
     if (!m_childContainmentLayer)
         return;
 
     m_childContainmentLayer->setPosition(FloatPoint(clippingBox.location() - localCompositingBounds.location() + roundedIntSize(m_owningLayer.subpixelAccumulation())));
     m_childContainmentLayer->setSize(clippingBox.size());
     m_childContainmentLayer->setOffsetFromRenderer(toIntSize(clippingBox.location()));
     if (m_childClippingMaskLayer && !m_scrollingLayer && !renderer()->style()->clipPath()) {
         m_childClippingMaskLayer->setPosition(m_childContainmentLayer->position());
@@ skipping 51 matching lines @@
         m_graphicsLayer->setTransformOrigin(compositedTransformOrigin);
     }
 }
 
 void CompositedLayerMapping::updateReflectionLayerGeometry(Vector<RenderLayer*>& layersNeedingPaintInvalidation)
 {
     if (!m_owningLayer.reflectionInfo() || !m_owningLayer.reflectionInfo()->reflectionLayer()->hasCompositedLayerMapping())
         return;
 
     CompositedLayerMappingPtr reflectionCompositedLayerMapping = m_owningLayer.reflectionInfo()->reflectionLayer()->compositedLayerMapping();
-    reflectionCompositedLayerMapping->updateGraphicsLayerGeometry(&m_owningLayer, layersNeedingPaintInvalidation);
+    reflectionCompositedLayerMapping->updateGraphicsLayerGeometry(&m_owningLayer, &m_owningLayer, layersNeedingPaintInvalidation);

[hartmanng, 2014/07/24 15:57:35]

Why is m_owningLayer necessarily the correct compositingStackingContext in this
case?

[Ian Vollick, 2014/07/24 17:39:09]

It's a great question. Having a reflection makes you a stacking context. (See
https://www.webkit.org/blog/182/css-reflections/).

The reflected* layout tests is to cover this case.

 }
 
 void CompositedLayerMapping::updateScrollingLayerGeometry(const IntRect& localCompositingBounds)
 {
     if (!m_scrollingLayer)
         return;
 
     ASSERT(m_scrollingContentsLayer);
     RenderBox* renderBox = toRenderBox(renderer());
     IntRect clientBox = enclosingIntRect(renderBox->clientBoxRect());
@@ skipping 145 matching lines @@
 
         if (m_childTransformLayer)
             superLayer = m_childTransformLayer.get();
 
         superLayer->addChild(m_scrollingLayer.get());
     }
 
     // The clip for child layers does not include space for overflow controls, so they exist as
     // siblings of the clipping layer if we have one. Normal children of this layer are set as
     // children of the clipping layer.
-    if (m_overflowControlsHostLayer)
+    if (m_overflowControlsClippingLayer) {
+        m_graphicsLayer->addChild(m_overflowControlsClippingLayer.get());
+        m_overflowControlsClippingLayer->addChild(m_overflowControlsHostLayer.get());
+    } else if (m_overflowControlsHostLayer) {
         m_graphicsLayer->addChild(m_overflowControlsHostLayer.get());
+    }
+
     if (m_layerForHorizontalScrollbar)
         m_overflowControlsHostLayer->addChild(m_layerForHorizontalScrollbar.get());
     if (m_layerForVerticalScrollbar)
         m_overflowControlsHostLayer->addChild(m_layerForVerticalScrollbar.get());
     if (m_layerForScrollCorner)
         m_overflowControlsHostLayer->addChild(m_layerForScrollCorner.get());
 
     // The squashing containment layer, if it exists, becomes a no-op parent.
     if (m_squashingLayer) {
         ASSERT(compositor()->layerSquashingEnabled());
@@ skipping 162 matching lines @@
 
 // Only a member function so it can call createGraphicsLayer.
 bool CompositedLayerMapping::toggleScrollbarLayerIfNeeded(OwnPtr<GraphicsLayer>& layer, bool needsLayer, CompositingReasons reason)
 {
     if (needsLayer == !!layer)
         return false;
     layer = needsLayer ? createGraphicsLayer(reason) : nullptr;
     return true;
 }
 
-bool CompositedLayerMapping::updateOverflowControlsLayers(bool needsHorizontalScrollbarLayer, bool needsVerticalScrollbarLayer, bool needsScrollCornerLayer)
+bool CompositedLayerMapping::updateOverflowControlsLayers(bool needsHorizontalScrollbarLayer, bool needsVerticalScrollbarLayer, bool needsScrollCornerLayer, bool needsAncestorClip)
 {
     bool horizontalScrollbarLayerChanged = toggleScrollbarLayerIfNeeded(m_layerForHorizontalScrollbar, needsHorizontalScrollbarLayer, CompositingReasonLayerForHorizontalScrollbar);
     bool verticalScrollbarLayerChanged = toggleScrollbarLayerIfNeeded(m_layerForVerticalScrollbar, needsVerticalScrollbarLayer, CompositingReasonLayerForVerticalScrollbar);
     bool scrollCornerLayerChanged = toggleScrollbarLayerIfNeeded(m_layerForScrollCorner, needsScrollCornerLayer, CompositingReasonLayerForScrollCorner);
 
     bool needsOverflowControlsHostLayer = needsHorizontalScrollbarLayer || needsVerticalScrollbarLayer || needsScrollCornerLayer;
     toggleScrollbarLayerIfNeeded(m_overflowControlsHostLayer, needsOverflowControlsHostLayer, CompositingReasonLayerForOverflowControlsHost);
+    bool needsOverflowClipLayer = needsOverflowControlsHostLayer && needsAncestorClip;
+    toggleScrollbarLayerIfNeeded(m_overflowControlsClippingLayer, needsOverflowClipLayer, CompositingReasonLayerForOverflowControlsHost);
 
     if (ScrollingCoordinator* scrollingCoordinator = scrollingCoordinatorFromLayer(m_owningLayer)) {
         if (horizontalScrollbarLayerChanged)
             scrollingCoordinator->scrollableAreaScrollbarLayerDidChange(m_owningLayer.scrollableArea(), HorizontalScrollbar);
         if (verticalScrollbarLayerChanged)
             scrollingCoordinator->scrollableAreaScrollbarLayerDidChange(m_owningLayer.scrollableArea(), VerticalScrollbar);
     }
 
     return horizontalScrollbarLayerChanged || verticalScrollbarLayerChanged || scrollCornerLayerChanged;
 }
@@ skipping 598 matching lines @@
 
 LayoutRect CompositedLayerMapping::contentsBox() const
 {
     LayoutRect contentsBox = contentsRect(renderer());
     contentsBox.move(contentOffsetInCompositingLayer());
     return contentsBox;
 }
 
 GraphicsLayer* CompositedLayerMapping::detachLayerForOverflowControls(const RenderLayer& enclosingLayer)
 {
-    LayoutPoint localOffsetToTransformedAncestor = m_owningLayer.computeOffsetFromTransformedAncestor();
-    LayoutPoint enclosingLayerOffsetToTransformedAncestor = enclosingLayer.computeOffsetFromTransformedAncestor();
-    m_overflowControlsHostLayer->setPosition(FloatPoint(localOffsetToTransformedAncestor - enclosingLayerOffsetToTransformedAncestor));
-    m_overflowControlsHostLayer->removeFromParent();
-    return m_overflowControlsHostLayer.get();
+    GraphicsLayer* host = m_overflowControlsClippingLayer.get();
+    if (!host)
+        host = m_overflowControlsHostLayer.get();
+    host->removeFromParent();
+    return host;
 }
 
 GraphicsLayer* CompositedLayerMapping::parentForSublayers() const
 {
     if (m_scrollingBlockSelectionLayer)
         return m_scrollingBlockSelectionLayer.get();
 
     if (m_scrollingContentsLayer)
         return m_scrollingContentsLayer.get();
 
@@ skipping 425 matching lines @@
     } else if (graphicsLayer == m_childClippingMaskLayer.get()) {
         name = "Child Clipping Mask Layer";
     } else if (graphicsLayer == m_layerForHorizontalScrollbar.get()) {
         name = "Horizontal Scrollbar Layer";
     } else if (graphicsLayer == m_layerForVerticalScrollbar.get()) {
         name = "Vertical Scrollbar Layer";
     } else if (graphicsLayer == m_layerForScrollCorner.get()) {
         name = "Scroll Corner Layer";
     } else if (graphicsLayer == m_overflowControlsHostLayer.get()) {
         name = "Overflow Controls Host Layer";
+    } else if (graphicsLayer == m_overflowControlsClippingLayer.get()) {
+        name = "Overflow Controls ClipLayer Layer";
     } else if (graphicsLayer == m_scrollingLayer.get()) {
         name = "Scrolling Layer";
     } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
         name = "Scrolling Contents Layer";
     } else if (graphicsLayer == m_scrollingBlockSelectionLayer.get()) {
         name = "Scrolling Block Selection Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink