Port of Android platform gesture detection code to C++

ui/events/gesture_detection/scale_gesture_detector.h

Index: ui/events/gesture_detection/scale_gesture_detector.h
diff --git a/ui/events/gesture_detection/scale_gesture_detector.h b/ui/events/gesture_detection/scale_gesture_detector.h
new file mode 100644
index 0000000000000000000000000000000000000000..9e84ca5e34fa0e1ff93f25d1dbb739aa22d67d4e
--- /dev/null
+++ b/ui/events/gesture_detection/scale_gesture_detector.h
@@ -0,0 +1,140 @@
+// 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_SCALE_GESTURE_DETECTOR_H_
+#define UI_EVENTS_GESTURE_DETECTION_SCALE_GESTURE_DETECTOR_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "base/time/time.h"
+#include "ui/events/gesture_detection/gesture_detection_export.h"
+#include "ui/events/gesture_detection/gesture_detector.h"
+
+namespace ui {
+
+class MotionEvent;
+
+// Port of ScaleGestureDetector.java from Android
+// * platform/frameworks/base/core/java/android/view/ScaleGestureDetector.java
+// * Change-Id: I3e7926a4f6f9ab4951f380bd004499c78b3bda69
+// * Please update the Change-Id as upstream Android changes are pulled.
+class ScaleGestureDetector : public GestureDetector::SimpleGestureListener {
+ public:
+  struct GESTURE_DETECTION_EXPORT Config {
+    Config();
+    ~Config();
+    GestureDetector::Config gesture_detector_config;
+    bool quick_scale_enabled;
+    int min_scaling_touch_major;
+    int min_scaling_span;
+  };
+
+  class ScaleGestureListener {
+   public:
+    virtual ~ScaleGestureListener() {}
+    virtual bool OnScale(const ScaleGestureDetector& detector) = 0;
+    virtual bool OnScaleBegin(const ScaleGestureDetector& detector) = 0;
+    virtual void OnScaleEnd(const ScaleGestureDetector& detector) = 0;
+  };
+
+  // A convenience class to extend when you only want to listen for a subset of
+  // scaling-related events. This implements all methods in
+  // |ScaleGestureListener| but does nothing.
+  // |OnScale()| returns false so that a subclass can retrieve the accumulated
+  // scale factor in an overridden |OnScaleEnd()|.
+  // |OnScaleBegin() returns true.
+  class SimpleScaleGestureListener : public ScaleGestureListener {
+   public:
+    // ScaleGestureListener implementation.
+    virtual bool OnScale(const ScaleGestureDetector&) OVERRIDE;
+    virtual bool OnScaleBegin(const ScaleGestureDetector&) OVERRIDE;
+    virtual void OnScaleEnd(const ScaleGestureDetector&) OVERRIDE;
+  };
+
+  ScaleGestureDetector(const Config& config, ScaleGestureListener* listener);
+  virtual ~ScaleGestureDetector();
+
+  // Accepts MotionEvents and dispatches events to a |ScaleGestureListener|
+  // when appropriate.
+  //
+  // Note: Applications should pass a complete and consistent event stream to
+  // this method. A complete and consistent event stream involves all
+  // MotionEvents from the initial ACTION_DOWN to the final ACTION_UP or
+  // ACTION_CANCEL.
+  //
+  // Returns true if the event was processed and the detector wants to receive
+  // the rest of the MotionEvents in this event stream.
+  bool OnTouchEvent(const MotionEvent& event);
+
+  // Set whether the associated |ScaleGestureListener| should receive
+  // OnScale callbacks when the user performs a doubletap followed by a swipe.
+  void SetQuickScaleEnabled(bool scales);
+  bool IsQuickScaleEnabled() const;
+  bool IsInProgress() const;
+  float GetFocusX() const;
+  float GetFocusY() const;
+  float GetCurrentSpan() const;
+  float GetCurrentSpanX() const;
+  float GetCurrentSpanY() const;
+  float GetPreviousSpan() const;
+  float GetPreviousSpanX() const;
+  float GetPreviousSpanY() const;
+  float GetScaleFactor() const;
+  base::TimeDelta GetTimeDelta() const;
+  base::TimeTicks GetEventTime() const;
+
+ private:
+  enum DoubleTapMode { DOUBLE_TAP_MODE_NONE, DOUBLE_TAP_MODE_IN_PROGRESS };
+
+  // DoubleTapListener implementation.
+  virtual bool OnDoubleTap(const MotionEvent& ev) OVERRIDE;
+
+  // The TouchMajor/TouchMinor elements of a MotionEvent can flutter/jitter on
+  // some hardware/driver combos. Smooth out to get kinder, gentler behavior.
+  void AddTouchHistory(const MotionEvent& ev);
+  void ClearTouchHistory();
+  bool InDoubleTapMode() const;
+
+  ScaleGestureListener* const listener_;
+
+  Config config_;
+
+  float focus_x_;
+  float focus_y_;
+
+  bool quick_scale_enabled_;
+
+  float curr_span_;
+  float prev_span_;
+  float initial_span_;
+  float curr_span_x_;
+  float curr_span_y_;
+  float prev_span_x_;
+  float prev_span_y_;
+  base::TimeTicks curr_time_;
+  base::TimeTicks prev_time_;
+  bool in_progress_;
+  int span_slop_;
+  int min_span_;
+
+  // Bounds for recently seen values.
+  float touch_upper_;
+  float touch_lower_;
+  float touch_history_last_accepted_;
+  int touch_history_direction_;
+  base::TimeTicks touch_history_last_accepted_time_;
+  int touch_min_major_;
+  float double_tap_focus_x_;
+  float double_tap_focus_y_;
+  DoubleTapMode double_tap_mode_;
+
+  bool event_before_or_above_starting_gesture_event_;
+
+  scoped_ptr<GestureDetector> gesture_detector_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScaleGestureDetector);
+};
+
+}  // namespace ui
+
+#endif  // UI_EVENTS_GESTURE_DETECTION_SCALE_GESTURE_DETECTOR_H_