Keeping track of descendants that draw content instead of recalcualting

cc/layers/layer_impl.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/layers/layer_impl.h"
 
 #include "base/debug/trace_event.h"
 #include "base/debug/trace_event_argument.h"
 #include "base/json/json_reader.h"
 #include "base/strings/stringprintf.h"
@@ skipping 46 matching lines @@
       use_parent_backface_visibility_(false),
       draw_checkerboard_for_missing_tiles_(false),
       draws_content_(false),
       hide_layer_and_subtree_(false),
       force_render_surface_(false),
       transform_is_invertible_(true),
       is_container_for_fixed_position_layers_(false),
       background_color_(0),
       opacity_(1.0),
       blend_mode_(SkXfermode::kSrcOver_Mode),
+      num_descendants_that_draw_content_(0),
       draw_depth_(0.f),
       needs_push_properties_(false),
       num_dependents_need_push_properties_(0),
       sorting_context_id_(0),
       current_draw_mode_(DRAW_MODE_NONE) {
   DCHECK_GT(layer_id_, 0);
   DCHECK(layer_tree_impl_);
   layer_tree_impl_->RegisterLayer(this);
   AnimationRegistrar* registrar = layer_tree_impl_->animationRegistrar();
   layer_animation_controller_ =
@@ skipping 92 matching lines @@
   SetNeedsPushProperties();
 }
 
 void LayerImpl::SetScrollChildren(std::set<LayerImpl*>* children) {
   if (scroll_children_.get() == children)
     return;
   scroll_children_.reset(children);
   SetNeedsPushProperties();
 }
 
+void LayerImpl::SetNumDescendantsThatDrawContent(int num_descendants) {
+  if (num_descendants_that_draw_content_ == num_descendants)
+    return;
+  num_descendants_that_draw_content_ = num_descendants;
+  SetNeedsPushProperties();
+}
+
 void LayerImpl::SetClipParent(LayerImpl* ancestor) {
   if (clip_parent_ == ancestor)
     return;
 
   clip_parent_ = ancestor;
   SetNeedsPushProperties();
 }
 
 void LayerImpl::SetClipChildren(std::set<LayerImpl*>* children) {
   if (clip_children_.get() == children)
@@ skipping 336 matching lines @@
   layer->SetTransformAndInvertibility(transform_, transform_is_invertible_);
 
   layer->SetScrollClipLayer(scroll_clip_layer_ ? scroll_clip_layer_->id()
                                                : Layer::INVALID_ID);
   layer->set_user_scrollable_horizontal(user_scrollable_horizontal_);
   layer->set_user_scrollable_vertical(user_scrollable_vertical_);
   layer->SetScrollOffsetAndDelta(
       scroll_offset_, layer->ScrollDelta() - layer->sent_scroll_delta());
   layer->SetSentScrollDelta(gfx::Vector2d());
   layer->Set3dSortingContextId(sorting_context_id_);
+  layer->SetNumDescendantsThatDrawContent(num_descendants_that_draw_content_);
 
   LayerImpl* scroll_parent = NULL;
   if (scroll_parent_) {
     scroll_parent = layer->layer_tree_impl()->LayerById(scroll_parent_->id());
     DCHECK(scroll_parent);
   }
 
   layer->SetScrollParent(scroll_parent);
   if (scroll_children_) {
     std::set<LayerImpl*>* scroll_children = new std::set<LayerImpl*>;
@@ skipping 969 matching lines @@
   return draw_properties_.last_drawn_render_surface_layer_list_id ==
          layer_tree_impl_->current_render_surface_list_id();
 }
 
 size_t LayerImpl::GPUMemoryUsageInBytes() const { return 0; }
 
 void LayerImpl::RunMicroBenchmark(MicroBenchmarkImpl* benchmark) {
   benchmark->RunOnLayer(this);
 }
 
+int LayerImpl::NumDescendantsThatDrawContent() const {
+  return num_descendants_that_draw_content_;
+}
+
 void LayerImpl::NotifyAnimationFinished(
     base::TimeTicks monotonic_time,
     Animation::TargetProperty target_property) {
   if (target_property == Animation::ScrollOffset)
     layer_tree_impl_->InputScrollAnimationFinished();
 }
 
 }  // namespace cc