snap_scroll_controller.cc 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#include "ui/events/gesture_detection/snap_scroll_controller.h"
6
7#include <cmath>
8
9#include "ui/events/gesture_detection/motion_event.h"
10
11namespace ui {
12namespace {
13const int kSnapBound = 16;
14}  // namespace
15
16SnapScrollController::Config::Config()
17    : screen_width_pixels(1), screen_height_pixels(1), device_scale_factor(1) {}
18
19SnapScrollController::Config::~Config() {}
20
21SnapScrollController::SnapScrollController(const Config& config)
22    : channel_distance_(CalculateChannelDistance(config)),
23      snap_scroll_mode_(SNAP_NONE),
24      first_touch_x_(-1),
25      first_touch_y_(-1),
26      distance_x_(0),
27      distance_y_(0) {}
28
29SnapScrollController::~SnapScrollController() {}
30
31void SnapScrollController::UpdateSnapScrollMode(float distance_x,
32                                                float distance_y) {
33  if (snap_scroll_mode_ == SNAP_HORIZ || snap_scroll_mode_ == SNAP_VERT) {
34    distance_x_ += std::abs(distance_x);
35    distance_y_ += std::abs(distance_y);
36    if (snap_scroll_mode_ == SNAP_HORIZ) {
37      if (distance_y_ > channel_distance_) {
38        snap_scroll_mode_ = SNAP_NONE;
39      } else if (distance_x_ > channel_distance_) {
40        distance_x_ = 0;
41        distance_y_ = 0;
42      }
43    } else {
44      if (distance_x_ > channel_distance_) {
45        snap_scroll_mode_ = SNAP_NONE;
46      } else if (distance_y_ > channel_distance_) {
47        distance_x_ = 0;
48        distance_y_ = 0;
49      }
50    }
51  }
52}
53
54void SnapScrollController::SetSnapScrollingMode(
55    const MotionEvent& event,
56    bool is_scale_gesture_detection_in_progress) {
57  switch (event.GetAction()) {
58    case MotionEvent::ACTION_DOWN:
59      snap_scroll_mode_ = SNAP_NONE;
60      first_touch_x_ = event.GetX();
61      first_touch_y_ = event.GetY();
62      break;
63    // Set scrolling mode to SNAP_X if scroll towards x-axis exceeds kSnapBound
64    // and movement towards y-axis is trivial.
65    // Set scrolling mode to SNAP_Y if scroll towards y-axis exceeds kSnapBound
66    // and movement towards x-axis is trivial.
67    // Scrolling mode will remain in SNAP_NONE for other conditions.
68    case MotionEvent::ACTION_MOVE:
69      if (!is_scale_gesture_detection_in_progress &&
70          snap_scroll_mode_ == SNAP_NONE) {
71        int x_diff = static_cast<int>(std::abs(event.GetX() - first_touch_x_));
72        int y_diff = static_cast<int>(std::abs(event.GetY() - first_touch_y_));
73        if (x_diff > kSnapBound && y_diff < kSnapBound) {
74          snap_scroll_mode_ = SNAP_HORIZ;
75        } else if (x_diff < kSnapBound && y_diff > kSnapBound) {
76          snap_scroll_mode_ = SNAP_VERT;
77        }
78      }
79      break;
80    case MotionEvent::ACTION_UP:
81    case MotionEvent::ACTION_CANCEL:
82      first_touch_x_ = -1;
83      first_touch_y_ = -1;
84      distance_x_ = 0;
85      distance_y_ = 0;
86      break;
87    default:
88      break;
89  }
90}
91
92// static
93float SnapScrollController::CalculateChannelDistance(const Config& config) {
94  float channel_distance = 16.f;
95
96  const float screen_size = std::abs(
97      hypot((float)config.screen_width_pixels / config.device_scale_factor,
98            (float)config.screen_height_pixels / config.device_scale_factor));
99  if (screen_size < 3.f) {
100    channel_distance = 16.f;
101  } else if (screen_size < 5.f) {
102    channel_distance = 22.f;
103  } else if (screen_size < 7.f) {
104    channel_distance = 28.f;
105  } else {
106    channel_distance = 34.f;
107  }
108  channel_distance = channel_distance * config.device_scale_factor;
109  if (channel_distance < 16.f)
110    channel_distance = 16.f;
111
112  return channel_distance;
113}
114
115}  // namespace ui
116