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 155 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()
+{
+    bool backgroundLayerPaintsOntoScrollingContentsLayer = shouldPaintBackgroundOntoScrollingContentsLayer();
+    if (backgroundLayerPaintsOntoScrollingContentsLayer != m_backgroundPaintsOntoScrollingContentsLayer)

[Stephen Chennney, 2016/08/22 19:16:04]

You never set m_backgroundPaintsOntoScrollingContentsLayer, as far as I can see.
Do it here?

I test that switched once then back again would fail, I suspect.

[flackr, 2016/08/22 19:33:25]

Oops, thank you for catching this. I suspect the other tests would have failed
as well. It now sets the flag and I've discovered I need to use setNeedsDisplay
(similar to the other update* methods in CLM) to dirty the layer.

+        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);
@@ skipping 436 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