CC Animations: Establish AnimationHost, AnimationTimeline and AnimationPlayer

cc/animation/animation_host.h

Index: cc/animation/animation_host.h
diff --git a/cc/animation/animation_host.h b/cc/animation/animation_host.h
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index 0000000000000000000000000000000000000000..e33560d156473e5df0344911f14b26be8a75367f
--- /dev/null
+++ b/cc/animation/animation_host.h
@@ -0,0 +1,97 @@
+// Copyright 2015 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.
+
+#ifndef CC_ANIMATION_ANIMATION_HOST_H_
+#define CC_ANIMATION_ANIMATION_HOST_H_
+
+#include <vector>
+
+#include "base/containers/hash_tables.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "cc/base/cc_export.h"
+
+namespace cc {
+
+class AnimationPlayer;
+class AnimationRegistrar;
+class AnimationTimeline;
+class LayerTreeHost;
+class LayerTreeMutatorsClient;
+
+typedef std::vector<scoped_refptr<AnimationTimeline>> AnimationTimelineList;
+
+// An AnimationHost contains all the state required to play animations.
+// Specifically, it owns all the AnimationTimelines objects.
+// There is just one AnimationHost for LayerTreeHost on main renderer thread
+// and just one AnimationHost for LayerTreeHostImpl on impl thread.
+// We synchronize them during the commit process in a one-way data flow process
+// (PushPropertiesTo).
+// An AnimationHost talks to it's correspondent LayerTreeHost via
+// LayerTreeMutatorsClient interface.
+// AnimationHost has it's own instance of AnimationRegistrar (to be merged).

[ajuma, 2015/04/30 13:17:54]

Nit: s/it's/its (also above and elsewhere)

[loyso (OOO), 2015/05/01 00:46:55]

Acknowledged.

[Ian Vollick, 2015/05/05 03:52:06]

To be clear, you mean that the AnimationRegistrar will eventually be merged into
AnimationHost?

[loyso (OOO), 2015/05/05 06:51:18]

Yes, correct.

[loyso (OOO), 2015/06/22 07:48:51]

Done.

[loyso (OOO), 2015/06/22 07:48:51]

Done.

+class CC_EXPORT AnimationHost {
+ public:
+  static scoped_ptr<AnimationHost> Create(bool is_impl_instance);
+  virtual ~AnimationHost();
+
+  void AddAnimationTimeline(AnimationTimeline* timeline);

[Ian Vollick, 2015/05/05 03:52:06]

If it's going to hold a reference to the animation timeline objects, should it
not pass a scoped_refptr to make transfer of ownership clear?

[loyso (OOO), 2015/05/05 06:51:18]

It would require a complete definition for AnimationTimeline class in all
translation units where we pass that pointer. Since we have a lot of obvious
plumbing and it's an intrusive RefCounting I've decided to go with forward
declarations. Changing this to scoped_refptr will require several #includes and
it will increase coupling. Plus some runtime overhead on passing.
Isn't it better to add a comment? =)

[Ian Vollick, 2015/05/07 13:58:42]

I don't think this is true; this appears to compile:
https://codereview.chromium.org/1131593007
I think this cost is negligible, and I prefer the clarity/safety of passing the
refptr. I know that in this case, you coerce the ptr into a scoped_refptr when
you add it to the vector, but in general, function(Thingy* thingy) is risky if
|thingy| is ref counted. If the callee hangs onto the ptr, it can end up with a
pointer to nothing if the caller decrements the ref count.

[loyso (OOO), 2015/05/08 01:04:34]

That's true for AnimationTimeline::AttachPlayer(AnimationPlayer* player) case.
web_compositor_animation_timeline_impl.cc can't be compiled w/o 
#include "cc/animation/animation_player.h"
But that's the only case. I agree with you completely - I'll change it to
scoped_refptr.

[loyso (OOO), 2015/06/22 07:48:51]

Done.

+  void RemoveAnimationTimeline(AnimationTimeline* timeline);
+  AnimationTimeline* GetTimelineById(int timeline_id) const;
+
+  void ClearTimelines();
+
+  void RegisterLayer(int layer_id, bool is_active_tree);

[Ian Vollick, 2015/05/05 03:52:06]

Please use an enum rather than a boolean. It makes the call sites easier to
read. Here and other places where you use a bool to mean "this is the impl
thread"

[loyso (OOO), 2015/05/05 06:51:18]

I wanted to go the LAC way with bools and no extra #include declarations
necessary since cc::Layers are deprecated. But yeah, I can add enum class.

[Ian Vollick, 2015/05/07 13:58:42]

Using bools was probably a mistake with LAC. I would prefer that you switch to
an enum here, but it's probably not worth updating the LAC to use it since it's
hopefully going away.

[loyso (OOO), 2015/05/08 01:04:34]

Acknowledged.

[loyso (OOO), 2015/06/22 07:48:51]

Done.

+  void UnregisterLayer(int layer_id, bool is_active_tree);
+
+  void RegisterPlayerForLayer(int layer_id, AnimationPlayer* player);
+  void UnregisterPlayerForLayer(int layer_id, AnimationPlayer* player);
+  AnimationPlayer* GetPlayerForLayerId(int layer_id) const;
+
+  // Parent LayerTreeHost or LayerTreeHostImpl.
+  LayerTreeMutatorsClient* layer_tree_mutators_client() {
+    return layer_tree_mutators_client_;
+  }
+  const LayerTreeMutatorsClient* layer_tree_mutators_client() const {
+    return layer_tree_mutators_client_;
+  }
+  void SetLayerTreeMutatorsClient(LayerTreeMutatorsClient* client);
+
+  void SetNeedsCommit();
+
+  void PushPropertiesTo(AnimationHost* host_impl);
+
+  AnimationRegistrar* animation_registrar() const {

[Ian Vollick, 2015/05/05 03:52:06]

This looks like it could be a reference given that the registrar is created in
the ctor and its lifetime is tied to the host's.

[loyso (OOO), 2015/05/05 06:51:18]

I preserved the accessor signature from LayerTreeHost/LayerTreeHostImpl where we
have identical situation (since AnimationRegistrar is marked for deletion).

[Ian Vollick, 2015/05/07 13:58:42]

I would prefer the reference, but if this accessor is temporary, then I don't
have strong feelings.

[loyso (OOO), 2015/06/22 07:48:51]

Let it be a reference (to be deleted)

+    return animation_registrar_.get();
+  }
+
+ private:
+  // TODO(loyso): Temporary 1:1 mapping. AnimationPlayers share
+  // LayerAnimationController for a given layer at the moment.
+  // Introduce LayersAnimations for the many AnimationPlayers to many Layers
+  // mapping (a CC counterpart for blink::ElementAnimations).
+  typedef base::hash_map<int, AnimationPlayer*> LayerToPlayerMap;
+  LayerToPlayerMap layer_to_player_map_;
+
+  explicit AnimationHost(bool is_impl_instance);
+
+  void PushTimelinesToImplThread(AnimationHost* host_impl) const;
+  void RemoveTimelinesFromImplThread(AnimationHost* host_impl) const;
+  void PushPropertiesToImplThread(AnimationHost* host_impl);
+
+  void EraseTimelines(AnimationTimelineList::iterator begin,
+                      AnimationTimelineList::iterator end);
+
+  AnimationTimelineList timelines_;
+  scoped_ptr<AnimationRegistrar> animation_registrar_;
+  LayerTreeMutatorsClient* layer_tree_mutators_client_;
+
+  const bool is_impl_instance_;
+
+  DISALLOW_COPY_AND_ASSIGN(AnimationHost);
+};
+
+}  // namespace cc
+
+#endif  // CC_ANIMATION_ANIMATION_HOST_H_