Support touch scroll gestures in menus.

ui/views/animation/scroll_animator.h

+// Copyright (c) 2012 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_VIEWS_ANIMATION_SCROLL_ANIMATOR_H_
+#define UI_VIEWS_ANIMATION_SCROLL_ANIMATOR_H_
+#pragma once
+
+#include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
+#include "ui/base/animation/animation_delegate.h"
+#include "ui/views/views_export.h"
+
+namespace ui {
+class SlideAnimation;
+}
+
+namespace views {
+
+class VIEWS_EXPORT ScrollDelegate {
+ public:
+  virtual void OnScroll(float dx, float dy) = 0;
+
+ protected:
+  ~ScrollDelegate() {}
+};
+
+class VIEWS_EXPORT ScrollAnimator : public ui::AnimationDelegate {
+ public:
+  // The ScrollAnimator does not own the delegate. Uses default acceleration.
+  explicit ScrollAnimator(ScrollDelegate* delegate);
+  virtual ~ScrollAnimator();
+
+  // Use this if you would prefer different acceleration than the default.
+  void set_acceleration(float acceleration) { acceleration_ = acceleration; }
+
+  void Start(float velocity_x, float velocity_y);
+  void Stop();
+
+  bool is_scrolling() const { return !!animation_.get(); }
+
+ private:
+  // Implementation of ui::AnimationDelegate.
+  virtual void AnimationEnded(const ui::Animation* animation) OVERRIDE;
+  virtual void AnimationProgressed(const ui::Animation* animation) OVERRIDE;
+  virtual void AnimationCanceled(const ui::Animation* animation) OVERRIDE;
+
+  ScrollDelegate* delegate_;
+
+  float velocity_x_;
+  float velocity_y_;
+  float last_t_;
+  float duration_;
+  float acceleration_;
+
+  scoped_ptr<ui::SlideAnimation> animation_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScrollAnimator);
+};
+
+}  // namespace views
+
+#endif  // UI_VIEWS_ANIMATION_SCROLL_ANIMATOR_H_