Explicit animation support

ui/gfx/compositor/layer_animation_element.h

+// Copyright (c) 2011 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 UI_GFX_COMPOSITOR_LAYER_ANIMATION_ELEMENT_H_
+#define UI_GFX_COMPOSITOR_LAYER_ANIMATION_ELEMENT_H_
+#pragma once
+
+#include <set>
+
+#include "base/time.h"
+#include "ui/gfx/compositor/compositor_export.h"
+
+namespace gfx {
+class Rect;
+}  // gfx
+
+namespace ui {
+
+class LayerAnimationDelegate;
+class Transform;
+
+// LayerAnimationElements represent one segment of an animation between two
+// keyframes. They know how to update a LayerAnimationDelegate given a value
+// between 0 and 1 (0 for the last keyframe, and one for the next).

[sky, 2011/10/19 00:06:33]

nit: the part in () is confusing. Maybe just 0 for initial, 1 for final?

+class COMPOSITOR_EXPORT LayerAnimationElement {
+ public:
+  enum AnimatableProperty {
+    TRANSFORM = 0,
+    BOUNDS,
+    OPACITY
+  };
+
+  typedef std::set<AnimatableProperty> AnimatableProperties;
+
+  static LayerAnimationElement* CreateTransformElement(

[sky, 2011/10/19 00:06:33]

each param on its own line when you wrap like this. Also document caller owns
return value.

+      const Transform& transform, base::TimeDelta duration);
+  static LayerAnimationElement* CreateBoundsElement(
+      const gfx::Rect& bounds, base::TimeDelta duration);
+  static LayerAnimationElement* CreateOpacityElement(
+      float opacity, base::TimeDelta duration);
+  static LayerAnimationElement* CreatePauseElement(
+      const AnimatableProperties& properties, base::TimeDelta duration);
+
+  virtual ~LayerAnimationElement() {}

[sky, 2011/10/19 00:06:33]

this should be before static methods.

+
+  // Updates the delegate to the appropriate value for |t|, which is in the
+  // range [0, 1] where 0 represents the last keyframe and 1 represents the

[sky, 2011/10/19 00:06:33]

same comment as with class description.

+  // next. If the animation is not aborted, it is guaranteed that Progress will
+  // eventually be called with t = 1.0.
+  virtual void Progress(double t, LayerAnimationDelegate* delegate) = 0;
+
+  // Called if the animation is not allowed to complete.

[sky, 2011/10/19 00:06:33]

Mention this may be invoked without a call to Progress (at least I think that's
the case).

+  virtual void Abort() = 0;
+
+  // The properties that the element modifies.
+  virtual const AnimatableProperties& Properties() const = 0;
+
+  // The duration of the animation
+  virtual base::TimeDelta Duration() const = 0;
+};
+
+}  // namespace ui
+
+#endif  // UI_GFX_COMPOSITOR_LAYER_ANIMATION_ELEMENT_H_