[Android] Port Scroller.java to C++ and use for fling animations

ui/gfx/android/scroller.h

+// Copyright 2014 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_ANDROID_SCROLLER_H_
+#define UI_GFX_ANDROID_SCROLLER_H_
+
+#include "base/time/time.h"
+#include "ui/gfx/gfx_export.h"
+
+namespace gfx {
+
+// Native port of android.widget.Scroller.
+// * Change-Id: I4365946f890a76fcfa78ca9d69f2a8e0848095a9
+// * Please update the Change-Id as upstream Android changes are pulled.
+class GFX_EXPORT Scroller {
+ public:
+  struct Config {
+    Config();
+
+    // Controls fling deceleration. Defaults to 0.015f.
+    float fling_friction;
+
+    // Controls fling accumulation. Defaults to disabled.
+    bool flywheel_enabled;
+  };
+
+  explicit Scroller(const Config& config);
+  ~Scroller();
+
+  // Start scrolling by providing a starting point and the distance to travel.
+  // The default value of 250 milliseconds will be used for the duration.
+  void StartScroll(float start_x,
+                   float start_y,
+                   float dx,
+                   float dy,
+                   base::TimeTicks start_time);
+
+  // Start scrolling by providing a starting point, the distance to travel,
+  // and the duration of the scroll.
+  void StartScroll(float start_x,
+                   float start_y,
+                   float dx,
+                   float dy,
+                   base::TimeTicks start_time,
+                   base::TimeDelta duration);
+
+  // Start scrolling based on a fling gesture. The distance travelled will
+  // depend on the initial velocity of the fling.
+  void Fling(float start_x,
+             float start_y,
+             float velocity_x,
+             float velocity_y,
+             float min_x,
+             float max_x,
+             float min_y,
+             float max_y,
+             base::TimeTicks start_time);
+
+  // Call this when you want to know the new location.  If it returns true,
+  // the animation is not yet finished.
+  bool ComputeScrollOffset(base::TimeTicks time);
+
+  // Extend the scroll animation by |extend|. This allows a running animation
+  // to scroll further and longer when used with |SetFinalX()| or |SetFinalY()|.
+  void ExtendDuration(base::TimeDelta extend);
+  void SetFinalX(float new_x);
+  void SetFinalY(float new_y);
+
+  // Stops the animation. Contrary to |ForceFinished()|, aborting the animation
+  // causes the scroller to move to the final x and y position.
+  void AbortAnimation();
+
+  // Terminate the scroll without affecting the current x and y positions.
+  void ForceFinished(bool finished);
+
+  // Returns whether the scroller has finished scrolling.
+  bool IsFinished() const;
+
+  // Returns the time elapsed since the beginning of the scrolling.
+  base::TimeDelta GetTimePassed() const;
+
+  // Returns how long the scroll event will take.
+  base::TimeDelta GetDuration() const;
+
+  float GetStartX() const;
+  float GetStartY() const;
+  float GetCurrX() const;
+  float GetCurrY() const;
+  float GetCurrVelocity() const;
+  float GetCurrVelocityX() const;
+  float GetCurrVelocityY() const;
+  float GetFinalX() const;
+  float GetFinalY() const;
+
+  bool IsScrollingInDirection(float xvel, float yvel) const;
+
+ private:
+  enum Mode {
+    UNDEFINED,
+    SCROLL_MODE,
+    FLING_MODE,
+  };
+
+  void OnDurationChanged();
+  void RecomputeDeltas();
+
+  double GetSplineDeceleration(float velocity) const;
+  base::TimeDelta GetSplineFlingDuration(float velocity) const;
+  double GetSplineFlingDistance(float velocity) const;
+
+  Mode mode_;
+
+  float start_x_;
+  float start_y_;
+  float final_x_;
+  float final_y_;
+
+  float min_x_;
+  float max_x_;
+  float min_y_;
+  float max_y_;
+
+  float curr_x_;
+  float curr_y_;
+  base::TimeTicks start_time_;
+  base::TimeTicks curr_time_;
+  base::TimeDelta duration_;
+  double duration_seconds_reciprocal_;
+  float delta_x_;
+  float delta_x_norm_;
+  float delta_y_;
+  float delta_y_norm_;
+  bool finished_;
+  bool flywheel_enabled_;
+
+  float velocity_;
+  float curr_velocity_;
+  float distance_;
+
+  float fling_friction_;
+  float deceleration_;
+  float tuning_coeff_;
+};
+
+}  // namespace gfx
+
+#endif  // UI_GFX_ANDROID_SCROLLER_H_