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// Copyright 2014 The Chromium Authors
// 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 <algorithm>
#include <cmath>
#include "ui/events/velocity_tracker/motion_event.h"
namespace ui {
namespace {
// Minimum ratio between initial X and Y motion to allow snapping.
const float kMinSnapRatio = 1.25f;
// Size of the snap rail relative to the initial snap bound threshold.
const float kSnapBoundToChannelMultiplier = 1.5f;
float CalculateChannelDistance(float snap_bound,
const gfx::SizeF& display_size) {
const float kMinChannelDistance = snap_bound * kSnapBoundToChannelMultiplier;
const float kMaxChannelDistance = kMinChannelDistance * 3.f;
const float kSnapChannelDipsPerScreenDip = kMinChannelDistance / 480.f;
if (display_size.IsEmpty())
return kMinChannelDistance;
float screen_size =
std::abs(hypot(static_cast<float>(display_size.width()),
static_cast<float>(display_size.height())));
float snap_channel_distance = screen_size * kSnapChannelDipsPerScreenDip;
return std::max(kMinChannelDistance,
std::min(kMaxChannelDistance, snap_channel_distance));
}
} // namespace
SnapScrollController::SnapScrollController(const gfx::SizeF& display_size)
: display_size_(display_size) {}
void SnapScrollController::SetSnapScrollMode(
const MotionEvent& event,
bool is_scale_gesture_detection_in_progress,
float slop_distance) {
switch (event.GetAction()) {
case MotionEvent::Action::DOWN:
mode_ = SNAP_PENDING;
down_position_.set_x(event.GetX());
down_position_.set_y(event.GetY());
break;
case MotionEvent::Action::MOVE: {
if (is_scale_gesture_detection_in_progress)
break;
if (mode_ != SNAP_PENDING)
break;
// Set scrolling mode to SNAP_X if scroll exceeds |slop_distance| and the
// ratio of x movement to y movement is sufficiently large. Similarly for
// SNAP_Y and y movement.
float dx = std::abs(event.GetX() - down_position_.x());
float dy = std::abs(event.GetY() - down_position_.y());
float kMinSnapBound = slop_distance;
float kMaxSnapBound = slop_distance * 2.f;
if (dx * dx + dy * dy > kMinSnapBound * kMinSnapBound) {
if (!dy || (dx / dy > kMinSnapRatio && dy < kMaxSnapBound))
mode_ = SNAP_HORIZ;
else if (!dx || (dy / dx > kMinSnapRatio && dx < kMaxSnapBound))
mode_ = SNAP_VERT;
}
if (mode_ == SNAP_PENDING && dx > kMaxSnapBound && dy > kMaxSnapBound)
mode_ = SNAP_NONE;
} break;
case MotionEvent::Action::UP:
case MotionEvent::Action::CANCEL:
down_position_ = gfx::PointF();
accumulated_distance_ = gfx::Vector2dF();
break;
default:
break;
}
}
void SnapScrollController::UpdateSnapScrollMode(float distance_x,
float distance_y,
float slop_distance) {
if (!IsSnappingScrolls())
return;
float channel_distance =
CalculateChannelDistance(slop_distance, display_size_);
accumulated_distance_ +=
gfx::Vector2dF(std::abs(distance_x), std::abs(distance_y));
if (mode_ == SNAP_HORIZ) {
if (accumulated_distance_.y() > channel_distance) {
mode_ = SNAP_NONE;
} else if (accumulated_distance_.x() > channel_distance) {
accumulated_distance_ = gfx::Vector2dF();
}
} else if (mode_ == SNAP_VERT) {
if (accumulated_distance_.x() > channel_distance) {
mode_ = SNAP_NONE;
} else if (accumulated_distance_.y() > channel_distance) {
accumulated_distance_ = gfx::Vector2dF();
}
}
}
bool SnapScrollController::IsSnapVertical() const {
return mode_ == SNAP_VERT;
}
bool SnapScrollController::IsSnapHorizontal() const {
return mode_ == SNAP_HORIZ;
}
bool SnapScrollController::IsSnappingScrolls() const {
return IsSnapHorizontal() || IsSnapVertical();
}
} // namespace ui
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