Repaint when background switches painting from/to scrolling contents layer.

third_party/WebKit/Source/core/layout/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 156 matching lines @@
     return (!page) ? nullptr : page->scrollingCoordinator();
 }
 
 CompositedLayerMapping::CompositedLayerMapping(PaintLayer& layer)
     : m_owningLayer(layer)
     , m_contentOffsetInCompositingLayerDirty(false)
     , m_pendingUpdateScope(GraphicsLayerUpdateNone)
     , m_isMainFrameLayoutViewLayer(false)
     , m_backgroundLayerPaintsFixedRootBackground(false)
     , m_scrollingContentsAreEmpty(false)
+    , m_backgroundPaintsOntoScrollingContentsLayer(false)
 {
     if (layer.isRootLayer() && layoutObject()->frame()->isMainFrame())
         m_isMainFrameLayoutViewLayer = true;
 
     createPrimaryGraphicsLayer();
 }
 
 CompositedLayerMapping::~CompositedLayerMapping()
 {
     // Hits in compositing/squashing/squash-onto-nephew.html.
@@ skipping 100 matching lines @@
 void CompositedLayerMapping::updateIsRootForIsolatedGroup()
 {
     bool isolate = m_owningLayer.shouldIsolateCompositedDescendants();
 
     // non stacking context layers should never isolate
     ASSERT(m_owningLayer.stackingNode()->isStackingContext() || !isolate);
 
     m_graphicsLayer->setIsRootForIsolatedGroup(isolate);
 }
 
+void CompositedLayerMapping::updateBackgroundPaintingLayer()

[chrishtr, 2016/08/24 23:35:32]

updateBackgroundPaintsOntoScrollingContentsLayer

[flackr, 2016/08/25 15:21:52]

Done.

+{
+    bool backgroundLayerPaintsOntoScrollingContentsLayer = shouldPaintBackgroundOntoScrollingContentsLayer();
+    if (backgroundLayerPaintsOntoScrollingContentsLayer != m_backgroundPaintsOntoScrollingContentsLayer) {
+        m_backgroundPaintsOntoScrollingContentsLayer = backgroundLayerPaintsOntoScrollingContentsLayer;
+        // If the background is no longer painted onto the scrolling contents
+        // layer the scrolling contents layer needs to be updated. If it is
+        // going to be painted onto the scrolling contents layer this update
+        // will be triggered by LayoutBoxModelObject::setBackingNeedsPaintInvalidationInRect
+        if (hasScrollingLayer() && !backgroundLayerPaintsOntoScrollingContentsLayer) {
+            m_scrollingContentsLayer->setNeedsDisplay();
+            m_owningLayer.setNeedsRepaint();
+        }
+    }
+}
+
 void CompositedLayerMapping::updateContentsOpaque()
 {
-    ASSERT(m_isMainFrameLayoutViewLayer || !m_backgroundLayer);
     if (isAcceleratedCanvas(layoutObject())) {
         // Determine whether the rendering context's external texture layer is opaque.
         CanvasRenderingContext* context = toHTMLCanvasElement(layoutObject()->node())->renderingContext();
         if (!context->hasAlpha())
             m_graphicsLayer->setContentsOpaque(true);
         else if (WebLayer* layer = context->platformLayer())
             m_graphicsLayer->setContentsOpaque(!Color(layer->backgroundColor()).hasAlpha());
         else
             m_graphicsLayer->setContentsOpaque(false);
     } else if (m_backgroundLayer) {
         m_graphicsLayer->setContentsOpaque(false);
         m_backgroundLayer->setContentsOpaque(m_owningLayer.backgroundIsKnownToBeOpaqueInRect(compositedBounds()));
     } else {
         // For non-root layers, background is painted by the scrolling contents layer if all backgrounds
         // are background attachment local, otherwise background is painted by the primary graphics layer.
-        if (hasScrollingLayer() && shouldPaintBackgroundOntoScrollingContentsLayer()) {
+        if (hasScrollingLayer() && m_backgroundPaintsOntoScrollingContentsLayer) {
             // Backgrounds painted onto the foreground are clipped by the padding box rect.
             // TODO(flackr): This should actually check the entire overflow rect within the
             // scrolling contents layer but since we currently only trigger this for solid
             // color backgrounds the answer will be the same.
             m_scrollingContentsLayer->setContentsOpaque(m_owningLayer.backgroundIsKnownToBeOpaqueInRect(toLayoutBox(layoutObject())->paddingBoxRect()));
 
             // When we paint the background onto the scrolling contents layer we are going
             // to leave a hole in the m_graphicsLayer where the background is so it is
             // not opaque.
             m_graphicsLayer->setContentsOpaque(false);
         } else {
+            if (hasScrollingLayer())
+                m_scrollingContentsLayer->setContentsOpaque(false);

[chrishtr, 2016/08/24 23:35:32]

Is this technically an unrelated fix?

Is it tested?

[flackr, 2016/08/25 15:21:52]

No, this is necessary to remove contents opaque flag when we switch from having
a background painted onto the scrolling contents layer to not.
Yes, in the added test the scrolling contents layer remains opaque (and turns
cyan in debug and usually black in release) when the background is no longer
painted into it if we don't call setContentsOpaque.

             m_graphicsLayer->setContentsOpaque(m_owningLayer.backgroundIsKnownToBeOpaqueInRect(compositedBounds()));
         }
     }
 }
 
 void CompositedLayerMapping::updateCompositedBounds()
 {
     ASSERT(m_owningLayer.compositor()->lifecycle().state() == DocumentLifecycle::InCompositingUpdate);
     // FIXME: if this is really needed for performance, it would be better to store it on Layer.
     m_compositedBounds = m_owningLayer.boundingBoxForCompositing();
@@ skipping 425 matching lines @@
 
     if (m_owningLayer.getScrollableArea() && m_owningLayer.getScrollableArea()->scrollsOverflow())
         m_owningLayer.getScrollableArea()->positionOverflowControls();
 
     updateLayerBlendMode(layoutObject()->styleRef());
     updateIsRootForIsolatedGroup();
     updateContentsRect();
     updateBackgroundColor();
     updateDrawsContent();
     updateElementIdAndCompositorMutableProperties();
+    updateBackgroundPaintingLayer();
     updateContentsOpaque();
     updateAfterPartResize();
     updateRenderingContext();
     updateShouldFlattenTransform();
     updateChildrenTransform();
     updateScrollParent(scrollParent());
     registerScrollingLayers();
 
     updateCompositingReasons();
 }
@@ skipping 1672 matching lines @@
     else if (compositor()->fixedRootBackgroundLayer() && m_owningLayer.isRootLayer())
         paintLayerFlags |= PaintLayerPaintingSkipRootBackground;
 
     if (graphicsLayer == m_graphicsLayer.get()
         || graphicsLayer == m_foregroundLayer.get()
         || graphicsLayer == m_backgroundLayer.get()
         || graphicsLayer == m_maskLayer.get()
         || graphicsLayer == m_childClippingMaskLayer.get()
         || graphicsLayer == m_scrollingContentsLayer.get()) {
 
-        bool paintRootBackgroundOntoScrollingContentsLayer = shouldPaintBackgroundOntoScrollingContentsLayer();
+        bool paintRootBackgroundOntoScrollingContentsLayer = m_backgroundPaintsOntoScrollingContentsLayer;
         DCHECK(!paintRootBackgroundOntoScrollingContentsLayer || (!m_backgroundLayer && !m_foregroundLayer));
         if (paintRootBackgroundOntoScrollingContentsLayer) {
             if (graphicsLayer == m_scrollingContentsLayer.get())
                 paintLayerFlags &= ~PaintLayerPaintingSkipRootBackground;
             else
                 paintLayerFlags |= PaintLayerPaintingSkipRootBackground;
         }
         GraphicsLayerPaintInfo paintInfo;
         paintInfo.paintLayer = &m_owningLayer;
         paintInfo.compositedBounds = compositedBounds();
@@ skipping 219 matching lines @@
     } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
         name = "Scrolling Contents Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink