text: // 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/macros.h"
  #include "ui/events/gesture_detection/gesture_detection_export.h"
  #include "ui/gfx/geometry/point_f.h"
  #include "ui/gfx/geometry/size_f.h"
  #include "ui/gfx/geometry/vector2d_f.h"
  
  namespace ui {
  
  class MotionEvent;
  
  // Port of SnapScrollController.java from Chromium
  // Controls the scroll snapping behavior based on scroll updates.
  class GESTURE_DETECTION_EXPORT SnapScrollController {
   public:
    SnapScrollController(float snap_bound, const gfx::SizeF& display_size);
    ~SnapScrollController();
  
    // Sets the snap scroll mode based on the event type.
    void SetSnapScrollMode(const MotionEvent& event,
                           bool is_scale_gesture_detection_in_progress);
  
    // 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);
  
    bool IsSnapVertical() const;
    bool IsSnapHorizontal() const;
    bool IsSnappingScrolls() const;
  
   private:
    enum SnapMode { SNAP_NONE, SNAP_PENDING, SNAP_HORIZ, SNAP_VERT };
  
    const float snap_bound_;
    const float channel_distance_;
    SnapMode mode_;
    gfx::PointF down_position_;
    gfx::Vector2dF accumulated_distance_;
  
    DISALLOW_COPY_AND_ASSIGN(SnapScrollController);
  };
  
  }  // namespace ui
  
  #endif  // UI_EVENTS_GESTURE_DETECTION_SNAP_SCROLL_CONTROLLER_H_
  