Fix the bug that negative outline-offset is covered up by composited

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp

Index: third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
index 8a84bb055d86c9b4bfe9f147a63bdde1442615f0..2bdebd2a8566142e305a88cba429147e6bb7bb64 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
@@ -559,6 +559,23 @@ bool CompositedLayerMapping::updateGraphicsLayerConfiguration() {
     scrollingConfigChanged = true;
   }
 
+  // The decoration layer is currently used for painting outline with certain
+  // offset that would be covered up by the composited scrolling contents layer
+  // and scrollbars.

[flackr, 2016/10/25 21:26:30]

Suggested wording:
If the outline needs to draw over the composited scrolling contents layer
or scrollbar layers it needs to be drawn into a separate layer.

[yigu, 2016/10/27 20:21:26]

Done.

+  int minBorderWidth =
+      std::min(layoutObject->style()->borderTopWidth(),
+               std::min(layoutObject->style()->borderLeftWidth(),
+                        std::min(layoutObject->style()->borderRightWidth(),
+                                 layoutObject->style()->borderBottomWidth())));
+  bool needsDecorationLayer =
+      m_owningLayer.getScrollableArea() &&
+      m_owningLayer.getScrollableArea()->usesCompositedScrolling() &&
+      layoutObject->style()->hasOutline() &&
+      layoutObject->style()->outlineOffset() < -minBorderWidth;
+
+  if (updateDecorationLayer(needsDecorationLayer))
+    layerConfigChanged = true;
+
   if (updateOverflowControlsLayers(
           requiresHorizontalScrollbarLayer(), requiresVerticalScrollbarLayer(),
           requiresScrollCornerLayer(), needsAncestorClip))
@@ -944,6 +961,11 @@ void CompositedLayerMapping::updateGraphicsLayerGeometry(
                           relativeCompositingBounds);
   updateForegroundLayerGeometry(contentsSize, clippingBox);
   updateBackgroundLayerGeometry(contentsSize);
+  // TODO(yigu): Currently the decoration layer uses the same contentSize
+  // as background layer and foreground layer. There are scenarios that
+  // the sizes could be different.
+  // The actual size of the decoration layer should be calculated separately.

[flackr, 2016/10/25 21:26:30]

nit: The size of the background layer should be different as well. We need to
check whether we are painting the decoration layer into the background and then
ignore or consider the outline when determining the contentsSize.

[yigu, 2016/10/27 20:21:26]

Added.

+  updateDecorationLayerGeometry(contentsSize);
   updateScrollingLayerGeometry(localCompositingBounds);
   updateChildClippingMaskLayerGeometry();
 
@@ -1371,6 +1393,20 @@ void CompositedLayerMapping::updateBackgroundLayerGeometry(
       m_graphicsLayer->offsetFromLayoutObject());
 }
 
+void CompositedLayerMapping::updateDecorationLayerGeometry(
+    const FloatSize& relativeCompositingBoundsSize) {
+  if (!m_decorationLayer)
+    return;
+  FloatSize decorationSize = relativeCompositingBoundsSize;
+  m_decorationLayer->setPosition(FloatPoint());
+  if (decorationSize != m_decorationLayer->size()) {
+    m_decorationLayer->setSize(decorationSize);
+    m_decorationLayer->setNeedsDisplay();
+  }
+  m_decorationLayer->setOffsetFromLayoutObject(
+      m_graphicsLayer->offsetFromLayoutObject());
+}
+
 void CompositedLayerMapping::registerScrollingLayers() {
   // Register fixed position layers and their containers with the scrolling
   // coordinator.
@@ -1438,6 +1474,10 @@ void CompositedLayerMapping::updateInternalHierarchy() {
   if (m_layerForScrollCorner)
     m_overflowControlsHostLayer->addChild(m_layerForScrollCorner.get());
 
+  // Now add the DecorationLayer as a subtree to GraphicsLayer
+  bottomLayer = m_graphicsLayer.get();
+  updateBottomLayer(m_decorationLayer.get());
+
   // The squashing containment layer, if it exists, becomes a no-op parent.
   if (m_squashingLayer) {
     ASSERT((m_ancestorClippingLayer && !m_squashingContainmentLayer) ||
@@ -1569,9 +1609,17 @@ void CompositedLayerMapping::updateDrawsContent() {
   if (m_foregroundLayer)
     m_foregroundLayer->setDrawsContent(hasPaintedContent);
 
+  // TODO(yigu): The background should no longer setDrawsContent(true) if we
+  // only have an outline (i.e. if there is nothing actually drawn into the

[flackr, 2016/10/25 21:26:30]

nit: "if we only have an outline and we're drawing the outline into the
decoration layer"

[yigu, 2016/10/27 20:21:26]

Added.

+  // background anymore.)
+  // "hasPaintedContent" should be calculated in a way that does not take the
+  // outline into consideration.
   if (m_backgroundLayer)
     m_backgroundLayer->setDrawsContent(hasPaintedContent);
 
+  if (m_decorationLayer)
+    m_decorationLayer->setDrawsContent(true);
+
   if (m_maskLayer)
     m_maskLayer->setDrawsContent(true);
 
@@ -1771,12 +1819,14 @@ enum ApplyToGraphicsLayersModeFlags {
       (1 << 6),  // layers between m_graphicsLayer and children
   ApplyToNonScrollingContentLayers = (1 << 7),
   ApplyToScrollingContentLayers = (1 << 8),
+  ApplyToDecorationLayer = (1 << 9),
   ApplyToAllGraphicsLayers =
       (ApplyToSquashingLayer | ApplyToScrollbarLayers | ApplyToBackgroundLayer |
        ApplyToMaskLayers |
        ApplyToLayersAffectedByPreserve3D |
        ApplyToContentLayers |
-       ApplyToScrollingContentLayers)
+       ApplyToScrollingContentLayers |
+       ApplyToDecorationLayer)
 };
 typedef unsigned ApplyToGraphicsLayersMode;
 
@@ -1839,6 +1889,11 @@ static void ApplyToGraphicsLayers(const CompositedLayerMapping* mapping,
     f(mapping->layerForVerticalScrollbar());
   if ((mode & ApplyToScrollbarLayers) && mapping->layerForScrollCorner())
     f(mapping->layerForScrollCorner());
+
+  if (((mode & ApplyToDecorationLayer) ||
+       (mode & ApplyToNonScrollingContentLayers)) &&
+      mapping->decorationLayer())
+    f(mapping->decorationLayer());
 }
 
 struct UpdateRenderingContextFunctor {
@@ -2017,6 +2072,23 @@ bool CompositedLayerMapping::updateBackgroundLayer(bool needsBackgroundLayer) {
   return layerChanged;
 }
 
+bool CompositedLayerMapping::updateDecorationLayer(bool needsDecorationLayer) {
+  bool layerChanged = false;
+  if (needsDecorationLayer) {
+    if (!m_decorationLayer) {
+      m_decorationLayer =
+          createGraphicsLayer(CompositingReasonLayerForDecoration);
+      m_decorationLayer->setPaintingPhase(GraphicsLayerPaintDecoration);
+      layerChanged = true;
+    }
+  } else if (m_decorationLayer) {
+    m_decorationLayer = nullptr;
+    layerChanged = true;
+  }
+
+  return layerChanged;
+}
+
 bool CompositedLayerMapping::updateMaskLayer(bool needsMaskLayer) {
   bool layerChanged = false;
   if (needsMaskLayer) {
@@ -2955,6 +3027,8 @@ void CompositedLayerMapping::paintContents(
     paintLayerFlags |= PaintLayerPaintingOverflowContents;
   if (graphicsLayerPaintingPhase & GraphicsLayerPaintCompositedScroll)
     paintLayerFlags |= PaintLayerPaintingCompositingScrollingPhase;
+  if (graphicsLayerPaintingPhase & GraphicsLayerPaintDecoration)
+    paintLayerFlags |= PaintLayerPaintingCompositingDecorationPhase;
 
   if (graphicsLayer == m_backgroundLayer.get())
     paintLayerFlags |= PaintLayerPaintingRootBackgroundOnly;
@@ -2967,7 +3041,8 @@ void CompositedLayerMapping::paintContents(
       graphicsLayer == m_backgroundLayer.get() ||
       graphicsLayer == m_maskLayer.get() ||
       graphicsLayer == m_childClippingMaskLayer.get() ||
-      graphicsLayer == m_scrollingContentsLayer.get()) {
+      graphicsLayer == m_scrollingContentsLayer.get() ||
+      graphicsLayer == m_decorationLayer.get()) {
     bool paintRootBackgroundOntoScrollingContentsLayer =
         m_backgroundPaintsOntoScrollingContentsLayer;
     DCHECK(!paintRootBackgroundOntoScrollingContentsLayer ||
@@ -3248,6 +3323,8 @@ String CompositedLayerMapping::debugName(
     name = "Scrolling Layer";
   } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
     name = "Scrolling Contents Layer";
+  } else if (graphicsLayer == m_decorationLayer.get()) {
+    name = "Decoration Layer";
   } else {
     ASSERT_NOT_REACHED();
   }