ui/events/gesture_detection/snap_scroll_controller.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef UI_EVENTS_GESTURE_DETECTION_SNAP_SCROLL_CONTROLLER_H_
   6 #define UI_EVENTS_GESTURE_DETECTION_SNAP_SCROLL_CONTROLLER_H_
   7
   8 #include "base/basictypes.h"
   9 #include "ui/events/gesture_detection/gesture_detection_export.h"
  10 #include "ui/gfx/geometry/point_f.h"
  11 #include "ui/gfx/geometry/size_f.h"
  12 #include "ui/gfx/geometry/vector2d_f.h"
  13
  14 namespace ui {
  15
  16 class MotionEvent;
  17
  18 // Port of SnapScrollController.java from Chromium
  19 // Controls the scroll snapping behavior based on scroll updates.
  20 class GESTURE_DETECTION_EXPORT SnapScrollController {
  21  public:
  22   SnapScrollController(float snap_bound, const gfx::SizeF& display_size);
  23   ~SnapScrollController();
  24
  25   // Sets the snap scroll mode based on the event type.
  26   void SetSnapScrollMode(const MotionEvent& event,
  27                          bool is_scale_gesture_detection_in_progress);
  28
  29   // Updates the snap scroll mode based on the given X and Y distance to be
  30   // moved on scroll.  If the scroll update is above a threshold, the snapping
  31   // behavior is reset.
  32   void UpdateSnapScrollMode(float distance_x, float distance_y);
  33
  34   bool IsSnapVertical() const;
  35   bool IsSnapHorizontal() const;
  36   bool IsSnappingScrolls() const;
  37
  38  private:
  39   enum SnapMode { SNAP_NONE, SNAP_PENDING, SNAP_HORIZ, SNAP_VERT };
  40
  41   const float snap_bound_;
  42   const float channel_distance_;
  43   SnapMode mode_;
  44   gfx::PointF down_position_;
  45   gfx::Vector2dF accumulated_distance_;
  46
  47   DISALLOW_COPY_AND_ASSIGN(SnapScrollController);
  48 };
  49
  50 }  // namespace ui
  51
  52 #endif  // UI_EVENTS_GESTURE_DETECTION_SNAP_SCROLL_CONTROLLER_H_