CC Animations: Make LayerAnimationController creation optional

ui/compositor/layer.cc

Index: ui/compositor/layer.cc
diff --git a/ui/compositor/layer.cc b/ui/compositor/layer.cc
index 34c11e3f7482729acd4225ead015b8a08ecefacd..f413daebba3c9eb73259acd76eb632ac5466b5d8 100644
--- a/ui/compositor/layer.cc
+++ b/ui/compositor/layer.cc
@@ -26,6 +26,7 @@
 #include "cc/output/filter_operation.h"
 #include "cc/output/filter_operations.h"
 #include "cc/resources/transferable_resource.h"
+#include "cc/trees/layer_tree_host.h"
 #include "ui/compositor/compositor_switches.h"
 #include "ui/compositor/dip_util.h"
 #include "ui/compositor/layer_animator.h"
@@ -124,7 +125,9 @@ Layer::~Layer() {
     layer_mask_back_link_->SetMaskLayer(NULL);
   for (size_t i = 0; i < children_.size(); ++i)
     children_[i]->parent_ = NULL;
-  cc_layer_->RemoveLayerAnimationEventObserver(this);
+
+  DetachObservers();
+
   cc_layer_->RemoveFromParent();
 }
 
@@ -142,17 +145,22 @@ float Layer::opacity() const {
 }
 
 void Layer::SetCompositor(Compositor* compositor) {

[ajuma, 2015/04/23 15:09:15]

This only gets called on the root layer, and only gets called with a non-null
compositor by Compositor::SetRootLayer. But later in the same call, the root
cc_layer gets added as a child of root_web_layer, which will lead to
cc::Layer::SetLayerTreeHost getting called on all the cc layers, which will lead
to them being registered. So the call to RegisterForAnimations below isn't
necessary, if we move AttachObservers so that it happens at the end of
Compositor::SetRootLayer.

[loyso (OOO), 2015/04/24 03:44:52]

Done.

+  if (compositor)
+    RegisterForAnimations(compositor);
+
   // This function must only be called to set the compositor on the root layer,
   // or to reset it.
   DCHECK(!compositor || !compositor_);
   DCHECK(!compositor || compositor->root_layer() == this);
   DCHECK(!parent_);
   if (compositor_) {
+    DetachObservers();
     RemoveAnimatorsInTreeFromCollection(
         compositor_->layer_animator_collection());
   }
   compositor_ = compositor;
   if (compositor) {
+    AttachObservers();
     OnDeviceScaleFactorChanged(compositor->device_scale_factor());
     SendPendingThreadedAnimations();
     AddAnimatorsInTreeToCollection(compositor_->layer_animator_collection());
@@ -167,8 +175,12 @@ void Layer::Add(Layer* child) {
   children_.push_back(child);
   cc_layer_->AddChild(child->cc_layer_);
   child->OnDeviceScaleFactorChanged(device_scale_factor_);
-  if (GetCompositor())
+  Compositor* compositor = GetCompositor();
+  if (compositor) {
+    child->RegisterForAnimations(compositor);

[ajuma, 2015/04/23 15:09:15]

The call to cc_layer_->AddChild(child->cc_layer_) above should lead to a call to
Layer::SetLayerTreeHost on child->cc_layer_ and all of its descendants, which in
turn will register these layers for animation, so there shouldn't be a need to
do that again here.

[loyso (OOO), 2015/04/24 03:44:52]

Done.

+    child->AttachObservers();
     child->SendPendingThreadedAnimations();
+  }
   LayerAnimatorCollection* collection = GetLayerAnimatorCollection();
   if (collection)
     child->AddAnimatorsInTreeToCollection(collection);
@@ -184,6 +196,8 @@ void Layer::Remove(Layer* child) {
   if (collection)
     child->RemoveAnimatorsInTreeFromCollection(collection);
 
+  child->DetachObservers();
+
   std::vector<Layer*>::iterator i =
       std::find(children_.begin(), children_.end(), child);
   DCHECK(i != children_.end());
@@ -490,7 +504,9 @@ void Layer::SwitchToLayer(scoped_refptr<cc::Layer> new_layer) {
     cc_layer_->parent()->ReplaceChild(cc_layer_, new_layer);
   }
   cc_layer_->SetLayerClient(NULL);
-  cc_layer_->RemoveLayerAnimationEventObserver(this);
+
+  DetachObservers();
+
   new_layer->SetOpacity(cc_layer_->opacity());
   new_layer->SetTransform(cc_layer_->transform());
   new_layer->SetPosition(cc_layer_->position());
@@ -503,7 +519,8 @@ void Layer::SwitchToLayer(scoped_refptr<cc::Layer> new_layer) {
   delegated_renderer_layer_ = NULL;
   surface_layer_ = NULL;
 
-  cc_layer_->AddLayerAnimationEventObserver(this);
+  AttachObservers();
+
   for (size_t i = 0; i < children_.size(); ++i) {
     DCHECK(children_[i]->cc_layer_);
     cc_layer_->AddChild(children_[i]->cc_layer_);
@@ -1041,11 +1058,36 @@ void Layer::CreateCcLayer() {
   cc_layer_->SetTransformOrigin(gfx::Point3F());
   cc_layer_->SetContentsOpaque(true);
   cc_layer_->SetIsDrawable(type_ != LAYER_NOT_DRAWN);
-  cc_layer_->AddLayerAnimationEventObserver(this);
   cc_layer_->SetLayerClient(this);
   RecomputePosition();
 }
 
+void Layer::RegisterForAnimations(Compositor* compositor) {
+  DCHECK(compositor);
+  const cc::LayerTreeHost& host = compositor->GetLayerTreeHost();
+
+  cc_layer_->RegisterForAnimations(host.animation_registrar(), host.settings());
+
+  for (size_t i = 0; i < children_.size(); ++i)
+    children_[i]->RegisterForAnimations(compositor);
+}
+
+void Layer::AttachObservers() {
+  if (cc_layer_->layer_animation_controller())
+    cc_layer_->AddLayerAnimationEventObserver(this);
+
+  for (size_t i = 0; i < children_.size(); ++i)
+    children_[i]->AttachObservers();
+}
+
+void Layer::DetachObservers() {
+  if (cc_layer_->layer_animation_controller())
+    cc_layer_->RemoveLayerAnimationEventObserver(this);
+
+  for (size_t i = 0; i < children_.size(); ++i)
+    children_[i]->DetachObservers();
+}
+
 gfx::Transform Layer::transform() const {
   return cc_layer_->transform();
 }