Allow proper highlighting on universal overflow scroll.

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 6ef931465ca5ec2478a3b9b03b3f81c2d50b8031..4a8c17cd3a676c9db6eed80ab26312b7f3ea0774 100644
--- a/Source/core/rendering/compositing/CompositedLayerMapping.cpp
+++ b/Source/core/rendering/compositing/CompositedLayerMapping.cpp
@@ -169,6 +169,7 @@ CompositedLayerMapping::CompositedLayerMapping(RenderLayer& layer)
     , m_backgroundLayerPaintsFixedRootBackground(false)
     , m_needToUpdateGraphicsLayer(false)
     , m_needToUpdateGraphicsLayerOfAllDecendants(false)
+    , m_scrollingContentsAreEmpty(false)
 {
     if (layer.isRootLayer() && renderer()->frame()->isMainFrame())
         m_isMainFrameRenderViewLayer = true;
@@ -252,6 +253,7 @@ void CompositedLayerMapping::destroyGraphicsLayers()
 
     m_scrollingLayer = nullptr;
     m_scrollingContentsLayer = nullptr;
+    m_scrollingBlockSelectionLayer = nullptr;
 }
 
 void CompositedLayerMapping::updateOpacity(const RenderStyle* style)
@@ -858,6 +860,8 @@ void CompositedLayerMapping::updateScrollingLayerGeometry(const IntRect& localCo
         m_foregroundLayer->setNeedsDisplay();
         m_foregroundLayer->setOffsetFromRenderer(m_scrollingContentsLayer->offsetFromRenderer());
     }
+
+    updateScrollingBlockSelection();
 }
 
 void CompositedLayerMapping::updateChildClippingMaskLayerGeometry()
@@ -1006,6 +1010,7 @@ void CompositedLayerMapping::updatePaintingPhases()
         if (!m_foregroundLayer)
             paintPhase |= GraphicsLayerPaintForeground;
         m_scrollingContentsLayer->setPaintingPhase(paintPhase);
+        m_scrollingBlockSelectionLayer->setPaintingPhase(paintPhase);
     }
 }
 
@@ -1014,6 +1019,31 @@ void CompositedLayerMapping::updateContentsRect()
     m_graphicsLayer->setContentsRect(pixelSnappedIntRect(contentsBox()));
 }
 
+void CompositedLayerMapping::updateScrollingBlockSelection()
+{
+    if (!m_scrollingBlockSelectionLayer)
+        return;
+
+    if (!m_scrollingContentsAreEmpty) {
+        m_scrollingBlockSelectionLayer->setDrawsContent(false);

[Ian Vollick, 2014/06/12 14:54:57]

A comment explaining that the selection will be painted into
m_scrollingContentsLayer would be nice here.

[hartmanng, 2014/06/13 14:51:38]

Done.

+        return;
+    }
+
+    const IntRect blockSelectionGapsBounds = m_owningLayer.blockSelectionGapsBounds();
+    const bool shouldDrawContent = !blockSelectionGapsBounds.isEmpty();
+    m_scrollingBlockSelectionLayer->setDrawsContent(shouldDrawContent);
+    if (!shouldDrawContent)
+        return;
+
+    const IntPoint position = blockSelectionGapsBounds.location() + m_owningLayer.scrollableArea()->adjustedScrollOffset();
+    if (m_scrollingBlockSelectionLayer->size() == blockSelectionGapsBounds.size() && m_scrollingBlockSelectionLayer->position() == position)
+        return;
+
+    m_scrollingBlockSelectionLayer->setPosition(position);
+    m_scrollingBlockSelectionLayer->setSize(blockSelectionGapsBounds.size());
+    m_scrollingBlockSelectionLayer->setOffsetFromRenderer(toIntSize(blockSelectionGapsBounds.location()), GraphicsLayer::SetNeedsDisplay);
+}
+
 void CompositedLayerMapping::updateDrawsContent()
 {
     if (m_scrollingLayer) {
@@ -1026,6 +1056,9 @@ void CompositedLayerMapping::updateDrawsContent()
 
         bool hasScrollingPaintedContent = m_owningLayer.hasVisibleContent() && (renderer()->hasBackground() || paintsChildren());

[Ian Vollick, 2014/06/12 14:54:57]

I don't think you need the temporary if you're going to stuff this value in
m_scrollingContentsAreEmpty

[hartmanng, 2014/06/13 14:51:38]

Done.

         m_scrollingContentsLayer->setDrawsContent(hasScrollingPaintedContent);
+
+        m_scrollingContentsAreEmpty = !hasScrollingPaintedContent;
+        updateScrollingBlockSelection();
         return;
     }
 
@@ -1409,6 +1442,10 @@ bool CompositedLayerMapping::updateScrollingLayers(bool needsScrollingLayers)
             m_scrollingContentsLayer->setDrawsContent(true);
             m_scrollingLayer->addChild(m_scrollingContentsLayer.get());
 
+            m_scrollingBlockSelectionLayer = createGraphicsLayer(CompositingReasonLayerForScrollingBlockSelection);

[Ian Vollick, 2014/06/12 14:54:57]

Is it possible to create this only when we have a selection?

[hartmanng, 2014/06/13 14:51:38]

I'm not really sure. I tried for a while, but couldn't find a good way. IIUC,
we'd have to trigger one of the heavier compositing updates for every change in
selection in order to get into the graphics layer configuration update code?
(ie, we would have to dirty m_needToUpdateGraphicsLayer, which would trigger a
lot of work through updateGraphicsLayerConfiguration and
updateInternalHierarchy).

+            m_scrollingBlockSelectionLayer->setDrawsContent(true);
+            m_scrollingContentsLayer->addChild(m_scrollingBlockSelectionLayer.get());
+
             layerChanged = true;
             if (scrollingCoordinator)
                 scrollingCoordinator->scrollableAreaScrollLayerDidChange(m_owningLayer.scrollableArea());
@@ -1416,6 +1453,7 @@ bool CompositedLayerMapping::updateScrollingLayers(bool needsScrollingLayers)
     } else if (m_scrollingLayer) {
         m_scrollingLayer = nullptr;
         m_scrollingContentsLayer = nullptr;
+        m_scrollingBlockSelectionLayer = nullptr;
         layerChanged = true;
         if (scrollingCoordinator)
             scrollingCoordinator->scrollableAreaScrollLayerDidChange(m_owningLayer.scrollableArea());
@@ -2049,7 +2087,8 @@ void CompositedLayerMapping::paintContents(const GraphicsLayer* graphicsLayer, G
         || graphicsLayer == m_backgroundLayer.get()
         || graphicsLayer == m_maskLayer.get()
         || graphicsLayer == m_childClippingMaskLayer.get()
-        || graphicsLayer == m_scrollingContentsLayer.get()) {
+        || graphicsLayer == m_scrollingContentsLayer.get()
+        || graphicsLayer == m_scrollingBlockSelectionLayer.get()) {
 
         GraphicsLayerPaintInfo paintInfo;
         paintInfo.renderLayer = &m_owningLayer;
@@ -2211,6 +2250,8 @@ String CompositedLayerMapping::debugName(const GraphicsLayer* graphicsLayer)
         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();
     }