Event smoothing in CrOS gesture recognizer.

ui/aura/gestures/velocity_calculator.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_AURA_GESTURES_VELOCITY_CALCULATOR_H_
+#define UI_AURA_GESTURES_VELOCITY_CALCULATOR_H_
+#pragma once
+
+#include <vector>
+#include "ui/aura/aura_export.h"
+#include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
+
+namespace aura {
+
+class AURA_EXPORT VelocityCalculator {
+ public:
+  explicit VelocityCalculator(int bufferSize);
+  ~VelocityCalculator() {}
+  void PointSeen(int x, int y, int64 time);
+  float XVelocity();
+  float YVelocity();
+  float VelocitySquared();
+  void ClearHistory();
+
+ private:
+  struct Point {
+    int x;
+    int y;
+    int64 time;
+  };
+
+  void UpdateVelocity();
+
+  typedef scoped_array<Point> HistoryBuffer;
+  HistoryBuffer buffer_;
+
+  // index_ points directly after the last point added
+  int index_;
+  size_t num_valid_entries_;
+  const size_t buffer_size_;
+  float x_velocity_;
+  float y_velocity_;
+  bool velocities_stale_;
+  DISALLOW_COPY_AND_ASSIGN(VelocityCalculator);
+};
+
+}  // namespace aura
+
+#endif  // UI_AURA_GESTURES_VELOCITY_CALCULATOR_H_