ui/events/gesture_detection/snap_scroll_controller.cc

   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 #include "ui/gfx/display.h"
  11
  12 namespace ui {
  13 namespace {
  14 const int kSnapBound = 16;
  15 const float kMinSnapChannelDistance = kSnapBound;
  16 const float kMaxSnapChannelDistance = kMinSnapChannelDistance * 3.f;
  17 const float kSnapChannelDipsPerScreenDip = kMinSnapChannelDistance / 480.f;
  18
  19 float CalculateChannelDistance(const gfx::Display& display) {
  20   if (display.bounds().IsEmpty())
  21     return kMinSnapChannelDistance;
  22
  23   float screen_size =
  24       std::abs(hypot(static_cast<float>(display.bounds().width()),
  25                      static_cast<float>(display.bounds().height())));
  26
  27   float snap_channel_distance = screen_size * kSnapChannelDipsPerScreenDip;
  28   return std::max(kMinSnapChannelDistance,
  29                   std::min(kMaxSnapChannelDistance, snap_channel_distance));
  30 }
  31
  32 }  // namespace
  33
  34
  35 SnapScrollController::SnapScrollController(const gfx::Display& display)
  36     : channel_distance_(CalculateChannelDistance(display)),
  37       snap_scroll_mode_(SNAP_NONE),
  38       first_touch_x_(-1),
  39       first_touch_y_(-1),
  40       distance_x_(0),
  41       distance_y_(0) {}
  42
  43 SnapScrollController::~SnapScrollController() {}
  44
  45 void SnapScrollController::UpdateSnapScrollMode(float distance_x,
  46                                                 float distance_y) {
  47   if (snap_scroll_mode_ == SNAP_HORIZ || snap_scroll_mode_ == SNAP_VERT) {
  48     distance_x_ += std::abs(distance_x);
  49     distance_y_ += std::abs(distance_y);
  50     if (snap_scroll_mode_ == SNAP_HORIZ) {
  51       if (distance_y_ > channel_distance_) {
  52         snap_scroll_mode_ = SNAP_NONE;
  53       } else if (distance_x_ > channel_distance_) {
  54         distance_x_ = 0;
  55         distance_y_ = 0;
  56       }
  57     } else {
  58       if (distance_x_ > channel_distance_) {
  59         snap_scroll_mode_ = SNAP_NONE;
  60       } else if (distance_y_ > channel_distance_) {
  61         distance_x_ = 0;
  62         distance_y_ = 0;
  63       }
  64     }
  65   }
  66 }
  67
  68 void SnapScrollController::SetSnapScrollingMode(
  69     const MotionEvent& event,
  70     bool is_scale_gesture_detection_in_progress) {
  71   switch (event.GetAction()) {
  72     case MotionEvent::ACTION_DOWN:
  73       snap_scroll_mode_ = SNAP_NONE;
  74       first_touch_x_ = event.GetX();
  75       first_touch_y_ = event.GetY();
  76       break;
  77     // Set scrolling mode to SNAP_X if scroll towards x-axis exceeds kSnapBound
  78     // and movement towards y-axis is trivial.
  79     // Set scrolling mode to SNAP_Y if scroll towards y-axis exceeds kSnapBound
  80     // and movement towards x-axis is trivial.
  81     // Scrolling mode will remain in SNAP_NONE for other conditions.
  82     case MotionEvent::ACTION_MOVE:
  83       if (!is_scale_gesture_detection_in_progress &&
  84           snap_scroll_mode_ == SNAP_NONE) {
  85         int x_diff = static_cast<int>(std::abs(event.GetX() - first_touch_x_));
  86         int y_diff = static_cast<int>(std::abs(event.GetY() - first_touch_y_));
  87         if (x_diff > kSnapBound && y_diff < kSnapBound) {
  88           snap_scroll_mode_ = SNAP_HORIZ;
  89         } else if (x_diff < kSnapBound && y_diff > kSnapBound) {
  90           snap_scroll_mode_ = SNAP_VERT;
  91         }
  92       }
  93       break;
  94     case MotionEvent::ACTION_UP:
  95     case MotionEvent::ACTION_CANCEL:
  96       first_touch_x_ = -1;
  97       first_touch_y_ = -1;
  98       distance_x_ = 0;
  99       distance_y_ = 0;
 100       break;
 101     default:
 102       break;
 103   }
 104 }
 105
 106 }  // namespace ui