Simplify content_layer attachment and viewporting logic.

chrome/browser/android/compositor/layer/thumbnail_layer.cc

 // Copyright 2014 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 "chrome/browser/android/compositor/layer/thumbnail_layer.h"
 
 #include "cc/layers/ui_resource_layer.h"
 #include "chrome/browser/android/thumbnail/thumbnail.h"
 #include "content/public/browser/android/compositor.h"
 #include "ui/gfx/geometry/size_conversions.h"
 
 namespace android {
 
 // static
 scoped_refptr<ThumbnailLayer> ThumbnailLayer::Create() {
   return make_scoped_refptr(new ThumbnailLayer());
 }
 
 void ThumbnailLayer::SetThumbnail(Thumbnail* thumbnail) {
   layer_->SetUIResourceId(thumbnail->ui_resource_id());
   UpdateSizes(thumbnail->scaled_content_size(), thumbnail->scaled_data_size());
 }
 
 void ThumbnailLayer::Clip(const gfx::Rect& clipping) {
   last_clipping_ = clipping;
+  clipped_ = true;
+
   gfx::Size clipped_content = gfx::Size(content_size_.width() - clipping.x(),
                                         content_size_.height() - clipping.y());
   clipped_content.SetToMin(clipping.size());
   layer_->SetBounds(clipped_content);
 
   layer_->SetUV(
       gfx::PointF(clipping.x() / resource_size_.width(),
                   clipping.y() / resource_size_.height()),
       gfx::PointF(
           (clipping.x() + clipped_content.width()) / resource_size_.width(),
           (clipping.y() + clipped_content.height()) / resource_size_.height()));
 }
 
+void ThumbnailLayer::ClearClip() {
+  layer_->SetUV(gfx::PointF(0.f, 0.f), gfx::PointF(1.f, 1.f));
+  layer_->SetBounds(gfx::Size(content_size_.width(), content_size_.height()));
+  clipped_ = false;
+}
+
 void ThumbnailLayer::AddSelfToParentOrReplaceAt(scoped_refptr<cc::Layer> parent,
                                                 size_t index) {
   if (index >= parent->children().size())
     parent->AddChild(layer_);
   else if (parent->child_at(index)->id() != layer_->id())
     parent->ReplaceChild(parent->child_at(index), layer_);
 }
 
 scoped_refptr<cc::Layer> ThumbnailLayer::layer() {
   return layer_;
 }
 
 ThumbnailLayer::ThumbnailLayer() : layer_(cc::UIResourceLayer::Create()) {
   layer_->SetIsDrawable(true);
 }
 
 ThumbnailLayer::~ThumbnailLayer() {
 }
 
 void ThumbnailLayer::UpdateSizes(const gfx::SizeF& content_size,
                                  const gfx::SizeF& resource_size) {
   if (content_size != content_size_ || resource_size != resource_size_) {
     content_size_ = content_size;
     resource_size_ = resource_size;
-    Clip(last_clipping_);
+    if (clipped_)
+      Clip(last_clipping_);
+    else
+      ClearClip();
   }
 }
 
 }  // namespace android