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// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "ui/events/gesture_detection/snap_scroll_controller.h"
#include <cmath>
#include "ui/events/gesture_detection/motion_event.h"
#include "ui/gfx/display.h"
namespace ui {
namespace {
const int kSnapBound = 16;
const float kMinSnapChannelDistance = kSnapBound;
const float kMaxSnapChannelDistance = kMinSnapChannelDistance * 3.f;
const float kSnapChannelDipsPerScreenDip = kMinSnapChannelDistance / 480.f;
float CalculateChannelDistance(const gfx::Display& display) {
if (display.bounds().IsEmpty())
return kMinSnapChannelDistance;
float screen_size =
std::abs(hypot(static_cast<float>(display.bounds().width()),
static_cast<float>(display.bounds().height())));
float snap_channel_distance = screen_size * kSnapChannelDipsPerScreenDip;
return std::max(kMinSnapChannelDistance,
std::min(kMaxSnapChannelDistance, snap_channel_distance));
}
} // namespace
SnapScrollController::SnapScrollController(const gfx::Display& display)
: channel_distance_(CalculateChannelDistance(display)),
snap_scroll_mode_(SNAP_NONE),
first_touch_x_(-1),
first_touch_y_(-1),
distance_x_(0),
distance_y_(0) {}
SnapScrollController::~SnapScrollController() {}
void SnapScrollController::UpdateSnapScrollMode(float distance_x,
float distance_y) {
if (snap_scroll_mode_ == SNAP_HORIZ || snap_scroll_mode_ == SNAP_VERT) {
distance_x_ += std::abs(distance_x);
distance_y_ += std::abs(distance_y);
if (snap_scroll_mode_ == SNAP_HORIZ) {
if (distance_y_ > channel_distance_) {
snap_scroll_mode_ = SNAP_NONE;
} else if (distance_x_ > channel_distance_) {
distance_x_ = 0;
distance_y_ = 0;
}
} else {
if (distance_x_ > channel_distance_) {
snap_scroll_mode_ = SNAP_NONE;
} else if (distance_y_ > channel_distance_) {
distance_x_ = 0;
distance_y_ = 0;
}
}
}
}
void SnapScrollController::SetSnapScrollingMode(
const MotionEvent& event,
bool is_scale_gesture_detection_in_progress) {
switch (event.GetAction()) {
case MotionEvent::ACTION_DOWN:
snap_scroll_mode_ = SNAP_NONE;
first_touch_x_ = event.GetX();
first_touch_y_ = event.GetY();
break;
// Set scrolling mode to SNAP_X if scroll towards x-axis exceeds kSnapBound
// and movement towards y-axis is trivial.
// Set scrolling mode to SNAP_Y if scroll towards y-axis exceeds kSnapBound
// and movement towards x-axis is trivial.
// Scrolling mode will remain in SNAP_NONE for other conditions.
case MotionEvent::ACTION_MOVE:
if (!is_scale_gesture_detection_in_progress &&
snap_scroll_mode_ == SNAP_NONE) {
int x_diff = static_cast<int>(std::abs(event.GetX() - first_touch_x_));
int y_diff = static_cast<int>(std::abs(event.GetY() - first_touch_y_));
if (x_diff > kSnapBound && y_diff < kSnapBound) {
snap_scroll_mode_ = SNAP_HORIZ;
} else if (x_diff < kSnapBound && y_diff > kSnapBound) {
snap_scroll_mode_ = SNAP_VERT;
}
}
break;
case MotionEvent::ACTION_UP:
case MotionEvent::ACTION_CANCEL:
first_touch_x_ = -1;
first_touch_y_ = -1;
distance_x_ = 0;
distance_y_ = 0;
break;
default:
break;
}
}
} // namespace ui
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