Replaced BackgroundAnimator with ShelfBackgroundAnimator.

ash/common/shelf/shelf_background_animator.h

Index: ash/common/shelf/shelf_background_animator.h
diff --git a/ash/common/shelf/shelf_background_animator.h b/ash/common/shelf/shelf_background_animator.h
new file mode 100644
index 0000000000000000000000000000000000000000..eebc8f3305af5f67bf414bee9ee0ccbcfac3d47f
--- /dev/null
+++ b/ash/common/shelf/shelf_background_animator.h
@@ -0,0 +1,128 @@
+// Copyright 2016 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 <vector>
+
+#include "ash/ash_export.h"
+#include "ash/common/shelf/wm_shelf_observer.h"
+#include "ash/common/wm/background_animator.h"
+#include "base/macros.h"
+#include "base/observer_list.h"
+
+namespace ash {
+
+namespace test {
+class ShelfBackgroundAnimatorTestApi;
+}  // namespace test
+
+class ShelfBackgroundAnimatorObserver;
+
+// Central controller for the Shelf and Dock opacity animations.
+//
+// The ShelfBackgroundAnimator is capable of observing a WmShelf instance but it
+// needs to be explicitly added as an observer.
+//
+// The Shelf currently uses 3 surfaces for the animations:
+//
+//  Non-Material Design:
+//    1. Shelf button backgrounds
+//    2. Opaque overlay for the SHELF_BACKGROUND_MAXIMIZED state.
+//    3. Shelf and Dock assets for the SHELF_BACKGROUND_OVERLAP state.

[James Cook, 2016/06/14 17:50:01]

So for material design, we don't have the overlap state? Or we do, but we don't
use assets for it? You might clarify that below.

[bruthig, 2016/07/26 19:50:02]

Attempted to clarify in comment.  WDYT?

+//  Material Design:
+//    1. Shelf button backgrounds
+//    2. Opaque overlay for THE SHELF_BACKGROUND_MAXIMIZED state.

[James Cook, 2016/06/14 17:50:01]

nit: THE -> the

[bruthig, 2016/07/26 19:50:02]

Done.

+class ASH_EXPORT ShelfBackgroundAnimator : public WmShelfObserver,
+                                           public BackgroundAnimatorDelegate {
+ public:
+  ShelfBackgroundAnimator();
+  ~ShelfBackgroundAnimator() override;
+
+  ShelfBackgroundType target_background_type() const {

[James Cook, 2016/06/14 17:50:01]

#include "ash/common/shelf/shelf_types.h" for ShelfBackgroundType

[bruthig, 2016/07/26 19:50:02]

Done.

+    return target_background_type_;
+  }
+
+  void AddObserver(ShelfBackgroundAnimatorObserver* observer);
+  void RemoveObserver(ShelfBackgroundAnimatorObserver* observer);
+
+  // Sets the |background_type| and notifies all the attached observers of the
+  // new background parameters (e.g. alpha). If |change_type| is
+  // BACKGROUND_CHANGE_IMMEDIATE then the observers will only receive one
+  // notification with the final background state, otherwise the observers will
+  // be notified multiple times in order to animate the changes to the
+  // backgrounds.
+  void PaintBackground(ShelfBackgroundType background_type,
+                       BackgroundAnimatorChangeType change_type);
+
+ protected:
+  // WmShelfObserver:
+  void OnBackgroundUpdated(ShelfBackgroundType background_type,
+                           BackgroundAnimatorChangeType change_type) override;
+
+  // BackgroundAnimatorDelegate:
+  void UpdateBackground(BackgroundAnimator* animator, int alpha) override;
+  void BackgroundAnimationEnded(BackgroundAnimator* animator,
+                                bool successful) override;
+
+ private:
+  friend class test::ShelfBackgroundAnimatorTestApi;
+
+  // Creates new BackgroundAnimators configured with the correct initial/target
+  // alpha values.  If any BackgroundAnimator's are currently animating they
+  // will be stopped.
+  void CreateAnimators(ShelfBackgroundType background_type,
+                       BackgroundAnimatorChangeType change_type);
+
+  // Stops all existing animators owned by this.
+  void StopAnimators();
+
+  // Configures all the BackgroundAnimators owned by this with the correct
+  // durations.
+  void ConfigureAnimators(ShelfBackgroundType background_type,
+                          BackgroundAnimatorChangeType change_type);
+
+  // The background type that this is animating towards or has reached.
+  ShelfBackgroundType target_background_type_;
+
+  // The last background type this is animating away from.
+  ShelfBackgroundType previous_background_type_;
+
+  // The last opaque background alpha value updated by the
+  // |opaque_background_animator_|.
+  int previous_opaque_background_alpha_;

[James Cook, 2016/06/14 17:50:01]

For my edification: Do we prefer ints for alpha or floats? I seem to recall
seeing sky@ land something recently that changed ints to floats in
ui/views/widget.h.

[bruthig, 2016/07/26 19:50:02]

I haven't dealt much in the opacity/alpha space but this is my take.  Alpha
values are ints in the inclusive [0, 255] range whereas opacities are float
values in the inclusive range [0.0f, 1.0f].  I am not aware of any 'preferred'
choice but I'm all for it if one exists.  As for this change I tried to limit
the delta and just used what BackgroundAnimator was already using.

+
+  // The last opaque background alpha value updated by the
+  // |asset_background_animator_|.
+  int previous_asset_background_alpha_;
+
+  // The last opaque background alpha value updated by the
+  // |item_background_animator_|.
+  int previous_item_background_alpha_;
+
+  // TODO(bruthig): Replace all BackgroundAnimators with a single
+  // gfx::SlideAnimation.
+  std::unique_ptr<BackgroundAnimator> opaque_background_animator_;

[James Cook, 2016/06/14 17:50:01]

nit: Comment which things are animated with this animator.

[bruthig, 2016/07/26 19:50:02]

Done.

+
+  // TODO(bruthig): Remove when non-md is no longer needed (crbug.com/614453).
+  std::unique_ptr<BackgroundAnimator> asset_background_animator_;
+
+  std::unique_ptr<BackgroundAnimator> item_background_animator_;
+
+  base::ObserverList<ShelfBackgroundAnimatorObserver> observers_;
+
+  // true if the existing BackgroundAnimators can be re-used to animate to the

[James Cook, 2016/06/14 17:50:01]

nit: true -> True and false -> False below

[bruthig, 2016/07/26 19:50:02]

Done.

+  // |previous_background_type_|. This allows for pre-empted animations to take
+  // the same amount of time to reverse to the |previous_background_type_|.
+  bool can_reuse_animators_;
+
+  // Tracks how many animators complete successfully since the last
+  // CreateAnimators() call. Used to properly set |can_reuse_animators_|.
+  int successful_animator_count_;
+
+  // false until an animation is triggered for the first time.
+  bool has_animated_once_;
+
+  DISALLOW_COPY_AND_ASSIGN(ShelfBackgroundAnimator);
+};

[James Cook, 2016/06/14 17:50:01]

Thanks for nice documentation through this class.

[bruthig, 2016/07/26 19:50:02]

:)

+
+}  // namespace ash