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// Copyright (c) 2012 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/views/animation/scroll_animator.h"
#include <algorithm>
#include <cmath>
#include "base/logging.h"
#include "ui/gfx/animation/slide_animation.h"
namespace {
const float kDefaultAcceleration = -1500.0f; // in pixels per second^2
// Assumes that d0 == 0.0f
float GetPosition(float v0, float a, float t) {
float max_t = -v0 / a;
if (t > max_t)
t = max_t;
return t * (v0 + 0.5f * a * t);
}
float GetDelta(float v0, float a, float t1, float t2) {
return GetPosition(v0, a, t2) - GetPosition(v0, a, t1);
}
} // namespace
namespace views {
ScrollAnimator::ScrollAnimator(ScrollDelegate* delegate)
: delegate_(delegate),
velocity_x_(0.0f),
velocity_y_(0.0f),
last_t_(0.0f),
duration_(0.0f),
acceleration_(kDefaultAcceleration) {
DCHECK(delegate);
}
ScrollAnimator::~ScrollAnimator() {
Stop();
}
void ScrollAnimator::Start(float velocity_x, float velocity_y) {
if (acceleration_ >= 0.0f)
acceleration_ = kDefaultAcceleration;
float v = std::max(fabs(velocity_x), fabs(velocity_y));
last_t_ = 0.0f;
velocity_x_ = velocity_x;
velocity_y_ = velocity_y;
duration_ = -v / acceleration_; // in seconds
animation_.reset(new gfx::SlideAnimation(this));
animation_->SetSlideDuration(static_cast<int>(duration_ * 1000));
animation_->Show();
}
void ScrollAnimator::Stop() {
velocity_x_ = velocity_y_ = last_t_ = duration_ = 0.0f;
animation_.reset();
}
void ScrollAnimator::AnimationEnded(const gfx::Animation* animation) {
Stop();
}
void ScrollAnimator::AnimationProgressed(const gfx::Animation* animation) {
float t = static_cast<float>(animation->GetCurrentValue()) * duration_;
float a_x = velocity_x_ > 0 ? acceleration_ : -acceleration_;
float a_y = velocity_y_ > 0 ? acceleration_ : -acceleration_;
float dx = GetDelta(velocity_x_, a_x, last_t_, t);
float dy = GetDelta(velocity_y_, a_y, last_t_, t);
last_t_ = t;
delegate_->OnScroll(dx, dy);
}
void ScrollAnimator::AnimationCanceled(const gfx::Animation* animation) {
Stop();
}
} // namespace views
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