Implement pinch-zoom scaling for main-frame scrollbars and pinch-zoom overlay scrollbars.

cc/scrollbar_layer.cc

 // Copyright 2012 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 "cc/scrollbar_layer.h"
 
 #include "base/basictypes.h"
 #include "base/debug/trace_event.h"
 #include "cc/caching_bitmap_content_layer_updater.h"
 #include "cc/layer_painter.h"
 #include "cc/layer_tree_host.h"
 #include "cc/prioritized_resource.h"
 #include "cc/resource_update_queue.h"
 #include "cc/scrollbar_layer_impl.h"
 #include "third_party/WebKit/Source/Platform/chromium/public/WebRect.h"
 #include "ui/gfx/rect_conversions.h"
 
 namespace cc {
 
 scoped_ptr<LayerImpl> ScrollbarLayer::CreateLayerImpl(
     LayerTreeImpl* tree_impl) {
-  return ScrollbarLayerImpl::Create(
-      tree_impl,
-      id(),
-      ScrollbarGeometryFixedThumb::create(make_scoped_ptr(geometry_->clone())))
-      .PassAs<LayerImpl>();
+  scoped_ptr<LayerImpl> scroll_layer_impl =
+      ScrollbarLayerImpl::Create(
+          tree_impl,
+          id(),
+          ScrollbarGeometryFixedThumb::create(
+              make_scoped_ptr(geometry_->clone()))).PassAs<LayerImpl>();
+
+  if (scroll_layer_id_ == Layer::PINCH_ZOOM_ROOT_SCROLL_LAYER_ID)
+    scroll_layer_impl->ToScrollbarLayer()->SetOpacity(0);

[enne (OOO), 2013/03/12 21:10:08]

Why are opacity updates blocked and this is required?

[wjmaclean, 2013/03/12 22:02:22]

The call to "ToScrollbarLayer()" is not necessary, but 

scroll_layer_impl->SetOpacity(0);

is. If you look at Layer::PushPropertiesTo(LayerImpl* layer)

you find

if (!OpacityIsAnimating())
  layer->SetOpacity(opacity_);
  
which is required for animations to work properly. If we piggyback on this then
we need to at least make sure the PZ ScrollbarLayerImpl starts with opacity = 0.

+
+  return scroll_layer_impl.Pass();
 }
 
 scoped_refptr<ScrollbarLayer> ScrollbarLayer::Create(
     scoped_ptr<WebKit::WebScrollbar> scrollbar,
     scoped_ptr<ScrollbarThemePainter> painter,
     scoped_ptr<WebKit::WebScrollbarThemeGeometry> geometry,
     int scrollLayerId) {
   return make_scoped_refptr(new ScrollbarLayer(scrollbar.Pass(),
                                                painter.Pass(),
                                                geometry.Pass(),
@@ skipping 17 matching lines @@
 ScrollbarLayer::~ScrollbarLayer() {}
 
 void ScrollbarLayer::SetScrollLayerId(int id) {
   if (id == scroll_layer_id_)
     return;
 
   scroll_layer_id_ = id;
   SetNeedsFullTreeSync();
 }
 
+bool ScrollbarLayer::OpacityIsAnimating() const {
+  return Layer::OpacityIsAnimating() ||

[enne (OOO), 2013/03/12 21:10:08]

Maybe just return Layer::OpacityIsAnimating || isOverlay() here, since we'll
need this for OSX overlay scrollbars too.

[wjmaclean, 2013/03/12 22:02:22]

Sure, though Clank also uses overlay scrollbars, and I don't know how this might
affect them.

+         scroll_layer_id_ == Layer::PINCH_ZOOM_ROOT_SCROLL_LAYER_ID;
+}
+
 WebKit::WebScrollbar::Orientation ScrollbarLayer::Orientation() const {
   return scrollbar_->orientation();
 }
 
 int ScrollbarLayer::MaxTextureSize() {
   DCHECK(layer_tree_host());
   return layer_tree_host()->rendererCapabilities().maxTextureSize;
 }
 
 float ScrollbarLayer::ClampScaleToMaxTextureSize(float scale) {
@@ skipping 348 matching lines @@
                thumb_.get(),
                origin_thumb_rect,
                queue,
                stats);
   }
 
   dirty_rect_ = gfx::RectF();
 }
 
 }  // namespace cc