Keeping track of descendants that draw content instead of recalcualting

cc/layers/layer.cc

Index: cc/layers/layer.cc
diff --git a/cc/layers/layer.cc b/cc/layers/layer.cc
index 82978daa03633a23d52b405414b4be0ead50b08c..6dc867132a06861319237824ac0299c4613b6721 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -47,6 +47,7 @@ Layer::Layer()
       parent_(NULL),
       layer_tree_host_(NULL),
       scroll_clip_layer_id_(INVALID_ID),
+      num_descendants_that_draw_content_(0),
       should_scroll_on_main_thread_(false),
       have_wheel_event_handlers_(false),
       have_scroll_event_handlers_(false),
@@ -55,6 +56,7 @@ Layer::Layer()
       is_root_for_isolated_group_(false),
       is_container_for_fixed_position_layers_(false),
       is_drawable_(false),
+      draws_content_(false),
       hide_layer_and_subtree_(false),
       masks_to_bounds_(false),
       contents_opaque_(false),
@@ -250,6 +252,8 @@ void Layer::InsertChild(scoped_refptr<Layer> child, size_t index) {
 
   index = std::min(index, children_.size());
   children_.insert(children_.begin() + index, child);
+  AddDrawableDescendants(child->NumDescendantsThatDrawContent() +
+                         (child->DrawsContent() ? 1 : 0));
   SetNeedsFullTreeSync();
 }
 
@@ -280,6 +284,8 @@ void Layer::RemoveChildOrDependent(Layer* child) {
       continue;
 
     child->SetParent(NULL);
+    RemoveDrawableDescendants(child->NumDescendantsThatDrawContent() +
+                              (child->DrawsContent() ? 1 : 0));
     children_.erase(iter);
     SetNeedsFullTreeSync();
     return;
@@ -779,6 +785,7 @@ void Layer::SetIsDrawable(bool is_drawable) {
     return;
 
   is_drawable_ = is_drawable;
+  UpdateDrawsContent(true);
   SetNeedsCommit();
 }
 
@@ -900,6 +907,7 @@ void Layer::PushPropertiesTo(LayerImpl* layer) {
     layer->SetTransformAndInvertibility(transform_, transform_is_invertible_);
   DCHECK(!(TransformIsAnimating() && layer->TransformIsAnimatingOnImplOnly()));
   layer->Set3dSortingContextId(sorting_context_id_);
+  layer->SetNumDescendantsThatDrawContent(num_descendants_that_draw_content_);
 
   layer->SetScrollClipLayer(scroll_clip_layer_id_);
   layer->set_user_scrollable_horizontal(user_scrollable_horizontal_);
@@ -1006,7 +1014,28 @@ scoped_ptr<LayerImpl> Layer::CreateLayerImpl(LayerTreeImpl* tree_impl) {
 }
 
 bool Layer::DrawsContent() const {
-  return is_drawable_;
+  return draws_content_;
+}
+
+void Layer::SetDrawsContent(bool draws_content) {
+  if (draws_content == draws_content_)
+    return;
+  if (parent()) {
+    if (draws_content) {
+      parent()->AddDrawableDescendants(1);
+    } else {
+      parent()->RemoveDrawableDescendants(1);
+    }
+  }
+  draws_content_ = draws_content;
+}
+
+void Layer::UpdateDrawsContent(bool draws_content) {

[danakj, 2014/07/14 15:49:23]

I like your idea about splitting this, how about this?

UpdateDrawsContent() {
  has_content = HasDrawableContent();  // This is virtual and returns true if
all the layer subtypes say true for this object. ie we pass by return value
instead of passing by parameter.
  draws_content = has_content && is_drawable_;
  ... inline the rest of SetDrawsContent here ...
}

[awoloszyn, 2014/07/14 19:38:33]

Done.

+  SetDrawsContent(draws_content && is_drawable_);
+}
+
+int Layer::NumDescendantsThatDrawContent() const {
+  return num_descendants_that_draw_content_;
 }
 
 void Layer::SavePaintProperties() {
@@ -1189,6 +1218,28 @@ void Layer::RemoveFromClipTree() {
   clip_parent_ = NULL;
 }
 
+void Layer::AddDrawableDescendants(int num) {

[danakj, 2014/07/14 15:49:23]

You only need one method here, the only difference in the two is += vs -=. Just
pass negative to remove a child and drop the Remove method?

[awoloszyn, 2014/07/14 19:38:33]

Done.

+  DCHECK_GE(num, 0);
+  DCHECK_GE(num_descendants_that_draw_content_, 0);
+  if (num == 0)
+    return;
+  num_descendants_that_draw_content_ += num;
+  SetNeedsCommit();
+  if (parent())
+    parent()->AddDrawableDescendants(num);
+}
+
+void Layer::RemoveDrawableDescendants(int num) {
+  DCHECK_GE(num, 0);
+  if (num == 0)
+    return;
+  num_descendants_that_draw_content_ -= num;
+  DCHECK_GE(num_descendants_that_draw_content_, 0);
+  SetNeedsCommit();
+  if (parent())
+    parent()->RemoveDrawableDescendants(num);
+}
+
 void Layer::RunMicroBenchmark(MicroBenchmark* benchmark) {
   benchmark->RunOnLayer(this);
 }