Support high DPI scrollbar on top level web frame.

cc/CCLayerTreeHost.cpp

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 
 #include "CCLayerTreeHost.h"
 
 #include "CCFontAtlas.h"
 #include "CCGraphicsContext.h"
@@ skipping 449 matching lines @@
         return;
 
     if (layoutViewportSize().isEmpty())
         return;
 
     m_contentsTextureManager->setMaxMemoryLimitBytes(memoryAllocationLimitBytes);
 
     updateLayers(rootLayer(), queue);
 }
 
-static void setScale(LayerChromium* layer, float deviceScaleFactor, float pageScaleFactor)
+static void setScale(LayerChromium* layer, float deviceScaleFactor, float pageScaleFactor, bool inScrollLayer)
 {
-    if (layer->boundsContainPageScale())
+    if (!inScrollLayer || layer->boundsContainPageScale())
         layer->setContentsScale(deviceScaleFactor);
     else
         layer->setContentsScale(deviceScaleFactor * pageScaleFactor);
 }
 
-static void updateLayerScale(LayerChromium* layer, float deviceScaleFactor, float pageScaleFactor)
+static void updateLayerScale(LayerChromium* layer, float deviceScaleFactor, float pageScaleFactor, bool inScrollLayer)
 {
-    setScale(layer, deviceScaleFactor, pageScaleFactor);
+    if (layer->scrollable())
+        inScrollLayer = true;

[flackr, 2012/09/17 19:37:51]

Alexandre, is the logic for finding the root scroll layer going to be changing?
This is the same logic as findRootScrollLayer in CCLayerTreeHostImpl.cpp.

[enne (OOO), 2012/09/17 20:37:00]

I think I'd prefer to keep this complexity outside of the compositor.  If a
browser compositor creates a layer tree, it's not necessarily going to want this
"outside root scroll layer" special case.  We already have a special case flag
to avoid this behavior: it's boundsContainPageScale.

I'd prefer if NonCompositedContentHost set this boundsContainPageScale flag on
itself and (recursively) all layers outside of the scroll layer, like
https://bugs.webkit.org/show_bug.cgi?id=77251 used to do for setting a different
flag on scrollbar layers.

That way the compositor doesn't have to know about this special case, and the
NonCompositedContentHost can contain all of this special case stuff about root
layers and root scrollbars.

+
+    setScale(layer, deviceScaleFactor, pageScaleFactor, inScrollLayer);
 
     LayerChromium* maskLayer = layer->maskLayer();
     if (maskLayer)
-        setScale(maskLayer, deviceScaleFactor, pageScaleFactor);
+        setScale(maskLayer, deviceScaleFactor, pageScaleFactor, inScrollLayer);
 
     LayerChromium* replicaMaskLayer = layer->replicaLayer() ? layer->replicaLayer()->maskLayer() : 0;
     if (replicaMaskLayer)
-        setScale(replicaMaskLayer, deviceScaleFactor, pageScaleFactor);
+        setScale(replicaMaskLayer, deviceScaleFactor, pageScaleFactor, inScrollLayer);
 
     const Vector<RefPtr<LayerChromium> >& children = layer->children();
     for (unsigned int i = 0; i < children.size(); ++i)
-        updateLayerScale(children[i].get(), deviceScaleFactor, pageScaleFactor);
+        updateLayerScale(children[i].get(), deviceScaleFactor, pageScaleFactor, inScrollLayer);
 }
 
 void CCLayerTreeHost::updateLayers(LayerChromium* rootLayer, CCTextureUpdateQueue& queue)
 {
     TRACE_EVENT0("cc", "CCLayerTreeHost::updateLayers");
 
-    updateLayerScale(rootLayer, m_deviceScaleFactor, m_pageScaleFactor);
+    updateLayerScale(rootLayer, m_deviceScaleFactor, m_pageScaleFactor, false);
 
     LayerList updateList;
 
     {
         TRACE_EVENT0("cc", "CCLayerTreeHost::updateLayers::calcDrawEtc");
         CCLayerTreeHostCommon::calculateDrawTransforms(rootLayer, deviceViewportSize(), m_deviceScaleFactor, rendererCapabilities().maxTextureSize, updateList);
         CCLayerTreeHostCommon::calculateVisibleRects(updateList);
     }
 
     // Reset partial texture update requests.
@@ skipping 269 matching lines @@
             else
                 layer->notifyAnimationFinished(wallClockTime);
         }
     }
 
     for (size_t childIndex = 0; childIndex < layer->children().size(); ++childIndex)
         setAnimationEventsRecursive(events, layer->children()[childIndex].get(), wallClockTime);
 }
 
 } // namespace cc