snap_scroll_controller.h revision a1401311d1ab56c4ed0a474bd38c108f75cb0cd9 
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
11namespace ui {
12
13class MotionEvent;
14class ZoomManager;
15
16// Port of SnapScrollController.java from Chromium
17// Controls the scroll snapping behavior based on scroll updates.
18class SnapScrollController {
19 public:
20  struct GESTURE_DETECTION_EXPORT Config {
21    Config();
22    ~Config();
23    int screen_width_pixels;
24    int screen_height_pixels;
25    float device_scale_factor;
26  };
27
28  explicit SnapScrollController(const Config& config);
29  ~SnapScrollController();
30
31  // Updates the snap scroll mode based on the given X and Y distance to be
32  // moved on scroll.  If the scroll update is above a threshold, the snapping
33  // behavior is reset.
34  void UpdateSnapScrollMode(float distance_x, float distance_y);
35
36  // Sets the snap scroll mode based on the event type.
37  void SetSnapScrollingMode(const MotionEvent& event,
38                            bool is_scale_gesture_detection_in_progress);
39
40  void ResetSnapScrollMode() { snap_scroll_mode_ = SNAP_NONE; }
41  bool IsSnapVertical() const { return snap_scroll_mode_ == SNAP_VERT; }
42  bool IsSnapHorizontal() const { return snap_scroll_mode_ == SNAP_HORIZ; }
43  bool IsSnappingScrolls() const { return snap_scroll_mode_ != SNAP_NONE; }
44
45 private:
46  enum SnapMode {
47    SNAP_NONE,
48    SNAP_HORIZ,
49    SNAP_VERT
50  };
51
52  static float CalculateChannelDistance(const Config& config);
53
54  float channel_distance_;
55  SnapMode snap_scroll_mode_;
56  float first_touch_x_;
57  float first_touch_y_;
58  float distance_x_;
59  float distance_y_;
60
61  DISALLOW_COPY_AND_ASSIGN(SnapScrollController);
62};
63
64}  // namespace ui
65
66#endif  // UI_EVENTS_GESTURE_DETECTION_SNAP_SCROLL_CONTROLLER_H_
67