src/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
  11 namespace ui {
  12 namespace {
  13
  14 // Minimum ratio between initial X and Y motion to allow snapping.
  15 const float kMinSnapRatio = 1.25f;
  16
  17 // Size of the snap rail relative to the initial snap bound threshold.
  18 const float kSnapBoundToChannelMultiplier = 1.5f;
  19
  20 float CalculateChannelDistance(float snap_bound,
  21                                const gfx::SizeF& display_size) {
  22   const float kMinChannelDistance = snap_bound * kSnapBoundToChannelMultiplier;
  23   const float kMaxChannelDistance = kMinChannelDistance * 3.f;
  24   const float kSnapChannelDipsPerScreenDip = kMinChannelDistance / 480.f;
  25   if (display_size.IsEmpty())
  26     return kMinChannelDistance;
  27
  28   float screen_size =
  29       std::abs(hypot(static_cast<float>(display_size.width()),
  30                      static_cast<float>(display_size.height())));
  31
  32   float snap_channel_distance = screen_size * kSnapChannelDipsPerScreenDip;
  33   return std::max(kMinChannelDistance,
  34                   std::min(kMaxChannelDistance, snap_channel_distance));
  35 }
  36
  37 }  // namespace
  38
  39 SnapScrollController::SnapScrollController(float snap_bound,
  40                                            const gfx::SizeF& display_size)
  41     : snap_bound_(snap_bound),
  42       channel_distance_(CalculateChannelDistance(snap_bound, display_size)),
  43       mode_(SNAP_NONE) {
  44 }
  45
  46 SnapScrollController::~SnapScrollController() {
  47 }
  48
  49 void SnapScrollController::SetSnapScrollMode(
  50     const MotionEvent& event,
  51     bool is_scale_gesture_detection_in_progress) {
  52   switch (event.GetAction()) {
  53     case MotionEvent::ACTION_DOWN:
  54       mode_ = SNAP_PENDING;
  55       down_position_.set_x(event.GetX());
  56       down_position_.set_y(event.GetY());
  57       break;
  58     case MotionEvent::ACTION_MOVE: {
  59       if (is_scale_gesture_detection_in_progress)
  60         break;
  61
  62       if (mode_ != SNAP_PENDING)
  63         break;
  64
  65       // Set scrolling mode to SNAP_X if scroll exceeds |snap_bound_| and the
  66       // ratio of x movement to y movement is sufficiently large. Similarly for
  67       // SNAP_Y and y movement.
  68       float dx = std::abs(event.GetX() - down_position_.x());
  69       float dy = std::abs(event.GetY() - down_position_.y());
  70       float kMinSnapBound = snap_bound_;
  71       float kMaxSnapBound = snap_bound_ * 2.f;
  72       if (dx * dx + dy * dy > kMinSnapBound * kMinSnapBound) {
  73         if (!dy || (dx / dy > kMinSnapRatio && dy < kMaxSnapBound))
  74           mode_ = SNAP_HORIZ;
  75         else if (!dx || (dy / dx > kMinSnapRatio && dx < kMaxSnapBound))
  76           mode_ = SNAP_VERT;
  77       }
  78
  79       if (mode_ == SNAP_PENDING && dx > kMaxSnapBound && dy > kMaxSnapBound)
  80         mode_ = SNAP_NONE;
  81     } break;
  82     case MotionEvent::ACTION_UP:
  83     case MotionEvent::ACTION_CANCEL:
  84       down_position_ = gfx::PointF();
  85       accumulated_distance_ = gfx::Vector2dF();
  86       break;
  87     default:
  88       break;
  89   }
  90 }
  91
  92 void SnapScrollController::UpdateSnapScrollMode(float distance_x,
  93                                                 float distance_y) {
  94   if (!IsSnappingScrolls())
  95     return;
  96
  97   accumulated_distance_ +=
  98       gfx::Vector2dF(std::abs(distance_x), std::abs(distance_y));
  99   if (mode_ == SNAP_HORIZ) {
 100     if (accumulated_distance_.y() > channel_distance_)
 101       mode_ = SNAP_NONE;
 102     else if (accumulated_distance_.x() > channel_distance_)
 103       accumulated_distance_ = gfx::Vector2dF();
 104   } else if (mode_ == SNAP_VERT) {
 105     if (accumulated_distance_.x() > channel_distance_)
 106       mode_ = SNAP_NONE;
 107     else if (accumulated_distance_.y() > channel_distance_)
 108       accumulated_distance_ = gfx::Vector2dF();
 109   }
 110 }
 111
 112 bool SnapScrollController::IsSnapVertical() const {
 113   return mode_ == SNAP_VERT;
 114 }
 115
 116 bool SnapScrollController::IsSnapHorizontal() const {
 117   return mode_ == SNAP_HORIZ;
 118 }
 119
 120 bool SnapScrollController::IsSnappingScrolls() const {
 121   return IsSnapHorizontal() || IsSnapVertical();
 122 }
 123
 124 }  // namespace ui