Drop background color optimization for composited layers

Source/core/rendering/compositing/CompositedLayerMapping.cpp

Index: Source/core/rendering/compositing/CompositedLayerMapping.cpp
diff --git a/Source/core/rendering/compositing/CompositedLayerMapping.cpp b/Source/core/rendering/compositing/CompositedLayerMapping.cpp
index 352a2c2eb93b04ef501000dfca5aa714af09251e..e82c3954c663f68fc33fdc19465e4fa3b376bb05 100644
--- a/Source/core/rendering/compositing/CompositedLayerMapping.cpp
+++ b/Source/core/rendering/compositing/CompositedLayerMapping.cpp
@@ -345,7 +345,7 @@ void CompositedLayerMapping::updateCompositedBounds()
 {
     // We need to know if we draw content in order to update our bounds (this has an effect
     // on whether or not descendands will paint into our backing). Update this value now.
-    updateDrawsContent(isSimpleContainerCompositingLayer());
+    updateDrawsContent();
 
     LayoutRect layerBounds = compositor()->calculateCompositedBounds(m_owningLayer, m_owningLayer);
 
@@ -513,7 +513,7 @@ bool CompositedLayerMapping::updateGraphicsLayerConfiguration()
         m_graphicsLayer->setReplicatedByLayer(0);
     }
 
-    updateBackgroundColor(isSimpleContainerCompositingLayer());
+    updateBackgroundColor();
 
     if (isDirectlyCompositedImage())
         updateImageContents();
@@ -631,8 +631,6 @@ void CompositedLayerMapping::updateGraphicsLayerGeometry()
     if (!hasActiveAnimationsOnCompositor(*renderer(), CSSPropertyOpacity))
         updateOpacity(renderer()->style());
 
-    bool isSimpleContainer = isSimpleContainerCompositingLayer();
-
     m_owningLayer->updateDescendantDependentFlags();
 
     // m_graphicsLayer is the corresponding GraphicsLayer for this RenderLayer and its non-compositing
@@ -853,9 +851,9 @@ void CompositedLayerMapping::updateGraphicsLayerGeometry()
         updateIsRootForIsolatedGroup();
     }
 
-    updateContentsRect(isSimpleContainer);
-    updateBackgroundColor(isSimpleContainer);
-    updateDrawsContent(isSimpleContainer);
+    updateContentsRect();
+    updateBackgroundColor();
+    updateDrawsContent();
     updateContentsOpaque();
     updateAfterWidgetResize();
     updateRenderingContext();
@@ -940,18 +938,12 @@ void CompositedLayerMapping::updateInternalHierarchy()
     }
 }
 
-void CompositedLayerMapping::updateContentsRect(bool isSimpleContainer)
+void CompositedLayerMapping::updateContentsRect()
 {
-    LayoutRect contentsRect;
-    if (isSimpleContainer && renderer()->hasBackground())
-        contentsRect = backgroundBox();
-    else
-        contentsRect = contentsBox();
-
-    m_graphicsLayer->setContentsRect(pixelSnappedIntRect(contentsRect));
+    m_graphicsLayer->setContentsRect(pixelSnappedIntRect(contentsBox()));
 }
 
-void CompositedLayerMapping::updateDrawsContent(bool isSimpleContainer)
+void CompositedLayerMapping::updateDrawsContent()
 {
     if (m_scrollingLayer) {
         // We don't have to consider overflow controls, because we know that the scrollbars are drawn elsewhere.
@@ -966,7 +958,7 @@ void CompositedLayerMapping::updateDrawsContent(bool isSimpleContainer)
         return;
     }
 
-    bool hasPaintedContent = containsPaintedContent(isSimpleContainer);
+    bool hasPaintedContent = containsPaintedContent();
     if (hasPaintedContent && isAcceleratedCanvas(renderer())) {
         CanvasRenderingContext* context = toHTMLCanvasElement(renderer()->node())->renderingContext();
         // Content layer may be null if context is lost.
@@ -1500,45 +1492,9 @@ Color CompositedLayerMapping::rendererBackgroundColor() const
     return backgroundRenderer->resolveColor(CSSPropertyBackgroundColor);
 }
 
-void CompositedLayerMapping::updateBackgroundColor(bool isSimpleContainer)
-{
-    Color backgroundColor = rendererBackgroundColor();
-    if (isSimpleContainer) {
-        m_graphicsLayer->setContentsToSolidColor(backgroundColor);
-        m_graphicsLayer->setBackgroundColor(Color::transparent);
-    } else {
-        m_graphicsLayer->setContentsToSolidColor(Color::transparent);
-        m_graphicsLayer->setBackgroundColor(backgroundColor);
-    }
-}
-
-static bool supportsDirectBoxDecorationsComposition(const RenderObject* renderer)
-{
-    if (renderer->hasClip())
-        return false;
-
-    if (hasBoxDecorationsOrBackgroundImage(renderer->style()))
-        return false;
-
-    // FIXME: we should be able to allow backgroundComposite; However since this is not a common use case it has been deferred for now.
-    if (renderer->style()->backgroundComposite() != CompositeSourceOver)
-        return false;
-
-    if (renderer->style()->backgroundClip() == TextFillBox)
-        return false;
-
-    return true;
-}
-
-bool CompositedLayerMapping::paintsBoxDecorations() const
+void CompositedLayerMapping::updateBackgroundColor()
 {
-    if (!m_owningLayer->hasVisibleBoxDecorations())
-        return false;
-
-    if (!supportsDirectBoxDecorationsComposition(renderer()))
-        return true;
-
-    return false;
+    m_graphicsLayer->setBackgroundColor(rendererBackgroundColor());
 }
 
 bool CompositedLayerMapping::paintsChildren() const
@@ -1557,23 +1513,21 @@ static bool isCompositedPlugin(RenderObject* renderer)
     return renderer->isEmbeddedObject() && toRenderEmbeddedObject(renderer)->allowsAcceleratedCompositing();
 }
 
-// A "simple container layer" is a RenderLayer which has no visible content to render.
-// It may have no children, or all its children may be themselves composited.
-// This is a useful optimization, because it allows us to avoid allocating backing store.
-bool CompositedLayerMapping::isSimpleContainerCompositingLayer() const
+// FIXME: it's O(n^2). A better solution is needed.
+bool CompositedLayerMapping::paintsIntoOwningLayer() const
 {
     RenderObject* renderObject = renderer();
     if (renderObject->hasMask()) // masks require special treatment
-        return false;
+        return true;
 
     if (renderObject->isReplaced() && !isCompositedPlugin(renderObject))
-        return false;
+        return true;
 
-    if (paintsBoxDecorations() || paintsChildren())
-        return false;
+    if (m_owningLayer->hasVisibleBoxDecorations() || paintsChildren())
+        return true;
 
     if (renderObject->isRenderRegion())
-        return false;
+        return true;
 
     if (renderObject->node() && renderObject->node()->isDocumentNode()) {
         // Look to see if the root object has a non-simple background
@@ -1586,7 +1540,7 @@ bool CompositedLayerMapping::isSimpleContainerCompositingLayer() const
         // Reject anything that has a border, a border-radius or outline,
         // or is not a simple background (no background, or solid color).
         if (hasBoxDecorationsOrBackgroundImage(style))
-            return false;
+            return true;
 
         // Now look at the body's renderer.
         HTMLElement* body = renderObject->document().body();
@@ -1597,10 +1551,9 @@ bool CompositedLayerMapping::isSimpleContainerCompositingLayer() const
         style = bodyObject->style();
 
         if (hasBoxDecorationsOrBackgroundImage(style))
-            return false;
+            return true;
     }
-
-    return true;
+    return false;
 }
 
 static bool hasVisibleNonCompositingDescendant(RenderLayer* parent)
@@ -1642,9 +1595,9 @@ bool CompositedLayerMapping::hasVisibleNonCompositingDescendantLayers() const
     return hasVisibleNonCompositingDescendant(m_owningLayer);
 }
 
-bool CompositedLayerMapping::containsPaintedContent(bool isSimpleContainer) const
+bool CompositedLayerMapping::containsPaintedContent() const
 {
-    if (isSimpleContainer || paintsIntoCompositedAncestor() || m_artificiallyInflatedBounds || m_owningLayer->isReflection())
+    if (!paintsIntoOwningLayer() || paintsIntoCompositedAncestor() || m_artificiallyInflatedBounds || m_owningLayer->isReflection())
         return false;
 
     if (isDirectlyCompositedImage())
@@ -1711,8 +1664,7 @@ void CompositedLayerMapping::updateImageContents()
 
     // This is a no-op if the layer doesn't have an inner layer for the image.
     m_graphicsLayer->setContentsToImage(image);
-    bool isSimpleContainer = false;
-    updateDrawsContent(isSimpleContainer);
+    updateDrawsContent();
 
     // Image animation is "lazy", in that it automatically stops unless someone is drawing
     // the image. So we have to kick the animation each time; this has the downside that the
@@ -1759,13 +1711,6 @@ LayoutRect CompositedLayerMapping::contentsBox() const
     return contentsBox;
 }
 
-IntRect CompositedLayerMapping::backgroundBox() const
-{
-    LayoutRect backgroundBox = backgroundRect(renderer());
-    backgroundBox.move(contentOffsetInCompostingLayer());
-    return pixelSnappedIntRect(backgroundBox);
-}
-
 GraphicsLayer* CompositedLayerMapping::parentForSublayers() const
 {
     if (m_scrollingContentsLayer)