[CRD iOS] Viewport fling animation

remoting/client/fling_tracker.h

+// Copyright 2017 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 REMOTING_CLIENT_FLING_TRACKER_H_
+#define REMOTING_CLIENT_FLING_TRACKER_H_
+
+#include "base/time/time.h"
+
+namespace remoting {
+
+// A class for tracking the positions of an object moving through a viscous
+// liquid.
+class FlingTracker {
+ public:
+  // time_constant: The larger the number the longer it takes to fling.
+  FlingTracker(float time_constant);
+
+  ~FlingTracker();
+
+  // Sets the position of the object and start fling. This will reset the
+  // existing fling.
+  void StartFling(float velocity_x, float velocity_y);
+
+  void StopFling();
+
+  bool IsFlingInProgress() const;
+
+  // Moves forward the object and catch up with |time|. The new positions will
+  // be writen to |x| and |y|.
+  // Returns true if the fling is still in progress at |time|, false otherwise,
+  // in which case |x| and |y| will not be touched.
+  bool TrackPositions(base::TimeTicks time, float* x, float* y);

[nicholss, 2017/05/10 19:34:05]

Might be simpler if you just return deltaX, deltaY

[Yuwei, 2017/05/10 23:28:24]

Done.

I was looking at the Android Scroller, which returns positions rather than
deltas...

+
+ private:
+  float time_constant_;
+  float initial_speed_rate_ = 0.f;
+  float velocity_ratio_x_ = 0.f;
+  float velocity_ratio_y_ = 0.f;
+  base::TimeTicks start_time_;
+
+  // FlingTracker is neither copyable nor movable.
+  FlingTracker(const FlingTracker&) = delete;
+  FlingTracker& operator=(const FlingTracker&) = delete;
+};
+
+}  // namespace remoting
+#endif  // REMOTING_CLIENT_FLING_TRACKER_H_