Port of Android platform gesture detection code to C++

ui/events/gesture_detection/snap_scroll_controller.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_SNAP_SCROLL_CONTROLLER_H_
+#define UI_EVENTS_GESTURE_DETECTION_SNAP_SCROLL_CONTROLLER_H_
+
+#include "base/basictypes.h"
+#include "ui/events/gesture_detection/gesture_detection_export.h"
+
+namespace ui {
+
+class MotionEvent;
+class ZoomManager;
+
+// Port of SnapScrollController.java from Chromium
+// Controls the scroll snapping behavior based on scroll updates.
+class SnapScrollController {
+ public:
+  struct GESTURE_DETECTION_EXPORT Config {
+    Config();
+    ~Config();
+    int screen_width_pixels;
+    int screen_height_pixels;
+    float device_scale_factor;
+  };
+
+  explicit SnapScrollController(const Config& config);
+  ~SnapScrollController();
+
+  // Updates the snap scroll mode based on the given X and Y distance to be
+  // moved on scroll.  If the scroll update is above a threshold, the snapping
+  // behavior is reset.
+  void UpdateSnapScrollMode(float distance_x, float distance_y);
+
+  // Sets the snap scroll mode based on the event type.
+  void SetSnapScrollingMode(const MotionEvent& event,
+                            bool is_scale_gesture_detection_in_progress);
+
+  void ResetSnapScrollMode() { snap_scroll_mode_ = SNAP_NONE; }
+  bool IsSnapVertical() const { return snap_scroll_mode_ == SNAP_VERT; }
+  bool IsSnapHorizontal() const { return snap_scroll_mode_ == SNAP_HORIZ; }
+  bool IsSnappingScrolls() const { return snap_scroll_mode_ != SNAP_NONE; }
+
+ private:
+  enum SnapMode {
+    SNAP_NONE,
+    SNAP_HORIZ,
+    SNAP_VERT
+  };
+
+  static float CalculateChannelDistance(const Config& config);
+
+  float channel_distance_;
+  SnapMode snap_scroll_mode_;
+  float first_touch_x_;
+  float first_touch_y_;
+  float distance_x_;
+  float distance_y_;
+
+  DISALLOW_COPY_AND_ASSIGN(SnapScrollController);
+};
+
+}  // namespace ui
+
+#endif  // UI_EVENTS_GESTURE_DETECTION_SNAP_SCROLL_CONTROLLER_H_