Port of Android platform gesture detection code to C++

ui/events/gesture_detection/velocity_tracker_state.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_EVENTS_GESTURE_DETECTION_VELOCITY_TRACKER_STATE_H_
+#define UI_EVENTS_GESTURE_DETECTION_VELOCITY_TRACKER_STATE_H_
+
+#include "base/basictypes.h"
+#include "ui/events/gesture_detection/bitset_32.h"
+#include "ui/events/gesture_detection/gesture_detection_export.h"
+#include "ui/events/gesture_detection/velocity_tracker.h"
+
+namespace ui {
+
+class MotionEvent;
+
+// Port of VelocityTrackerState from Android
+// * platform/frameworks/base/core/jni/android_view_VelocityTracker.cpp
+// * Change-Id: I3517881b87b47dcc209d80dbd0ac6b5cf29a766f
+// * Please update the Change-Id as upstream Android changes are pulled.
+class GESTURE_DETECTION_EXPORT VelocityTrackerState {
+ public:
+  VelocityTrackerState();
+  explicit VelocityTrackerState(VelocityTracker::Strategy strategy);
+  ~VelocityTrackerState();
+
+  void Clear();
+  void AddMovement(const MotionEvent& event);
+  void ComputeCurrentVelocity(int32_t units, float max_velocity);
+  float GetXVelocity(int32_t id) const;
+  float GetYVelocity(int32_t id) const;
+
+ private:
+  struct Velocity {
+    float vx, vy;
+  };
+
+  void GetVelocity(int32_t id, float* out_vx, float* out_vy) const;
+
+  VelocityTracker velocity_tracker_;
+  int32_t active_pointer_id_;
+  BitSet32 calculated_id_bits_;
+  Velocity calculated_velocity_[VelocityTracker::MAX_POINTERS];
+
+  DISALLOW_COPY_AND_ASSIGN(VelocityTrackerState);
+};
+
+}  // namespace ui
+
+#endif  // UI_EVENTS_GESTURE_DETECTION_VELOCITY_TRACKER_STATE_H_