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

cc/layer_tree_impl.cc

 // 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 "cc/layer_tree_impl.h"
 
 #include "base/debug/trace_event.h"
 #include "cc/heads_up_display_layer_impl.h"
 #include "cc/layer_tree_host_common.h"
 #include "cc/layer_tree_host_impl.h"
+#include "cc/scrollbar_layer_impl.h"
 #include "ui/gfx/vector2d_conversions.h"
 
 namespace cc {
 
 LayerTreeImpl::LayerTreeImpl(LayerTreeHostImpl* layer_tree_host_impl)
     : layer_tree_host_impl_(layer_tree_host_impl),
       source_frame_number_(-1),
       hud_layer_(0),
       root_scroll_layer_(0),
       currently_scrolling_layer_(0),
@@ skipping 88 matching lines @@
     target_tree->SetViewportSizeInvalid();
   else
     target_tree->ResetViewportSizeInvalid();
 
   if (hud_layer())
     target_tree->set_hud_layer(static_cast<HeadsUpDisplayLayerImpl*>(
         LayerTreeHostCommon::findLayerInSubtree(
             target_tree->RootLayer(), hud_layer()->id())));
   else
     target_tree->set_hud_layer(NULL);
+
+  target_tree->SetPinchZoomHorizontalLayerId(pinch_zoom_scrollbar_horizontal_layer_id);
+  target_tree->SetPinchZoomVerticalLayerId(pinch_zoom_scrollbar_vertical_layer_id);
 }
 
 LayerImpl* LayerTreeImpl::RootScrollLayer() {
   DCHECK(IsActiveTree());
   return root_scroll_layer_;
 }
 
 LayerImpl* LayerTreeImpl::CurrentlyScrollingLayer() {
   DCHECK(IsActiveTree());
   return currently_scrolling_layer_;
@@ skipping 350 matching lines @@
   LayerIteratorType end = LayerIteratorType::end(&render_surface_layer_list_);
   for (LayerIteratorType it = LayerIteratorType::begin(
            &render_surface_layer_list_); it != end; ++it) {
     if (!it.representsItself())
       continue;
     state->Append((*it)->AsValue().release());
   }
   return state.PassAs<base::Value>();
 }
 
+void LayerTreeImpl::SetPinchZoomHorizontalLayerId(int layer_id) {
+  pinch_zoom_scrollbar_horizontal_layer_id = layer_id;
+}
+
+ScrollbarLayerImpl* LayerTreeImpl::PinchZoomScrollbarHorizontal() {
+  return static_cast<ScrollbarLayerImpl*>(LayerById(
+    pinch_zoom_scrollbar_horizontal_layer_id));
+}
+
+void LayerTreeImpl::SetPinchZoomVerticalLayerId(int layer_id) {
+  pinch_zoom_scrollbar_vertical_layer_id = layer_id;
+}
+
+ScrollbarLayerImpl* LayerTreeImpl::PinchZoomScrollbarVertical() {
+  return static_cast<ScrollbarLayerImpl*>(LayerById(
+    pinch_zoom_scrollbar_vertical_layer_id));
+}
+
+void LayerTreeImpl::UpdatePinchZoomScrollbarsIfNeeded() {
+  LayerImpl* rootScrollLayer = RootScrollLayer();
+  if (!rootScrollLayer || (rootScrollLayer != CurrentlyScrollingLayer()))
+    return;
+
+  if (ScrollbarLayerImpl* scrollbar = PinchZoomScrollbarHorizontal()) {
+    scrollbar->setCurrentPos(rootScrollLayer->scrollOffset().x());
+    scrollbar->setTotalSize(rootScrollLayer->bounds().width());
+    scrollbar->setMaximum(rootScrollLayer->maxScrollOffset().x());
+  }
+  if (ScrollbarLayerImpl* scrollbar = PinchZoomScrollbarVertical()) {
+    scrollbar->setCurrentPos(rootScrollLayer->scrollOffset().y());
+    scrollbar->setTotalSize(rootScrollLayer->bounds().height());
+    scrollbar->setMaximum(rootScrollLayer->maxScrollOffset().y());
+  }
+}
+
+void LayerTreeImpl::SetPinchZoomScrollbarsVisibility() {
+  LayerImpl* rootScrollLayer = RootScrollLayer();
+  bool pinchZoomScrollbarShouldDraw = rootScrollLayer &&
+        rootScrollLayer == CurrentlyScrollingLayer() &&
+        total_page_scale_factor() > 1;
+
+  float opacity = pinchZoomScrollbarShouldDraw ? 0.5 : 0;

[jamesr, 2013/02/26 20:48:46]

0.5 seems like another magical value - where does it come from?

[wjmaclean, 2013/03/01 15:30:32]

Fixed.

+
+  if (ScrollbarLayerImpl* scrollbar = PinchZoomScrollbarHorizontal())
+    scrollbar->setOpacity(opacity);
+
+  if (ScrollbarLayerImpl* scrollbar = PinchZoomScrollbarVertical())
+    scrollbar->setOpacity(opacity);
+}
+
 } // namespace cc