Create Pinch Virtual Viewport scrollbar layers in Blink.

Source/web/WebViewImpl.cpp

 /*
  * Copyright (C) 2011, 2012 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 13 matching lines @@
  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #include "config.h"
 #include "WebViewImpl.h"
 
+#include "core/rendering/RenderLayerCompositor.h"
 #include "public/platform/Platform.h"
 #include "public/platform/WebDragData.h"
 #include "public/platform/WebFloatPoint.h"
 #include "public/platform/WebGestureCurve.h"
 #include "public/platform/WebImage.h"
 #include "public/platform/WebLayer.h"
 #include "public/platform/WebLayerTreeView.h"
 #include "public/platform/WebPoint.h"
 #include "public/platform/WebRect.h"
 #include "public/platform/WebString.h"
@@ skipping 3752 matching lines @@
 
     if (page()->settings().pinchVirtualViewportEnabled()) {
         if (!m_pinchViewports)
             m_pinchViewports = PinchViewports::create(this);
 
         m_pinchViewports->setOverflowControlsHostLayer(layer);
         m_pinchViewports->setViewportSize(mainFrameImpl()->frame()->view()->frameRect().size());
         if (layer) {
             m_rootGraphicsLayer = m_pinchViewports->rootGraphicsLayer();
             m_rootLayer = m_pinchViewports->rootGraphicsLayer()->platformLayer();
-            m_pinchViewports->registerViewportLayersWithTreeView(m_layerTreeView);
         } else {
             m_rootGraphicsLayer = 0;
             m_rootLayer = 0;
-            m_pinchViewports->clearViewportLayersForTreeView(m_layerTreeView);
         }
     } else {
         m_rootGraphicsLayer = layer;
         m_rootLayer = layer ? layer->platformLayer() : 0;
     }
 
     setIsAcceleratedCompositingActive(layer);
 
     if (m_layerTreeView) {
-        if (m_rootLayer)
+        if (m_rootLayer) {
             m_layerTreeView->setRootLayer(*m_rootLayer);
-        else
+            // We register viewport layers here since there may not be a layer
+            // tree view prior to this point.
+            if (m_pinchViewports) {
+                m_pinchViewports->registerViewportLayersWithTreeView(m_layerTreeView);
+            } else {
+                GraphicsLayer* rootScrollLayer = compositor()->scrollLayer();
+                rootScrollLayer->platformLayer()->setScrollClipLayer(m_rootLayer);

[enne (OOO), 2013/09/12 18:51:21]

I don't think the root layer is the clip layer for the root scroll layer.  The
clip layer is one of the children, right?  Can you do this where the clip layer
/ root scroll layer is created rather than here?  The same comment applies to
PinchViewports::registerViewportLayersWithTreeView.

(I also think it's a little bit indirect to store the clip layer on a scroll
layer since it's really information for the scrollbars that just happen to be on
that scrollbar.  I think this is workable though; it's just some design
awkwardness, I think.)

[wjmaclean, 2013/09/12 19:01:56]

Oops, you're right ... I'll fix this.
This happens in RenderLayerCompositor, which doesn't (at present) ever seem to
deal with the WebLayer interface ... is it OK to add it there?
This is doable.
 
I thought if I gave the clip layer info to the scroll layer, then the scrollbar
could just accept values computed by the scroll layer, and never have to worry
about where they come from. The scroll layer can do one set of computations for
one or two scrollbars in the same call. I thought this seemed a bit cleaner, but
if it becomes unworkable it can change. :-)

+                m_layerTreeView->registerViewportLayers(m_rootLayer, rootScrollLayer->platformLayer(), 0);
+            }
+        } else {
             m_layerTreeView->clearRootLayer();
+            if (m_pinchViewports)
+                m_pinchViewports->clearViewportLayersForTreeView(m_layerTreeView);
+            else
+                m_layerTreeView->clearViewportLayers();
+        }
     }
 
     suppressInvalidations(false);
 }
 
 void WebViewImpl::scheduleCompositingLayerSync()
 {
     m_layerTreeView->setNeedsRedraw();
 }
 
@@ skipping 279 matching lines @@
     //    the initial viewport width.
     // 2. The author has disabled viewport zoom.
 
     const PageScaleConstraints& constraints = m_pageScaleConstraintsSet.pageDefinedConstraints();
 
     return fixedLayoutSize().width == m_size.width
         || (constraints.minimumScale == constraints.maximumScale && constraints.minimumScale != -1);
 }
 
 } // namespace WebKit