1// Copyright 2013 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 "cc/animation/scroll_offset_animation_curve.h"
6
7#include <algorithm>
8#include <cmath>
9
10#include "base/logging.h"
11#include "cc/animation/timing_function.h"
12#include "ui/gfx/animation/tween.h"
13
14const double kDurationDivisor = 60.0;
15
16namespace cc {
17
18namespace {
19
20static float MaximumDimension(gfx::Vector2dF delta) {
21  return std::max(std::abs(delta.x()), std::abs(delta.y()));
22}
23
24static base::TimeDelta DurationFromDelta(gfx::Vector2dF delta) {
25  // The duration of a scroll animation depends on the size of the scroll.
26  // The exact relationship between the size and the duration isn't specified
27  // by the CSSOM View smooth scroll spec and is instead left up to user agents
28  // to decide. The calculation performed here will very likely be further
29  // tweaked before the smooth scroll API ships.
30  return base::TimeDelta::FromMicroseconds(
31      (std::sqrt(MaximumDimension(delta)) / kDurationDivisor) *
32      base::Time::kMicrosecondsPerSecond);
33}
34
35static scoped_ptr<TimingFunction> EaseOutWithInitialVelocity(double velocity) {
36  // Based on EaseInOutTimingFunction::Create with first control point rotated.
37  const double r2 = 0.42 * 0.42;
38  const double v2 = velocity * velocity;
39  const double x1 = std::sqrt(r2 / (v2 + 1));
40  const double y1 = std::sqrt(r2 * v2 / (v2 + 1));
41  return CubicBezierTimingFunction::Create(x1, y1, 0.58, 1)
42      .PassAs<TimingFunction>();
43}
44
45}  // namespace
46
47scoped_ptr<ScrollOffsetAnimationCurve> ScrollOffsetAnimationCurve::Create(
48    const gfx::Vector2dF& target_value,
49    scoped_ptr<TimingFunction> timing_function) {
50  return make_scoped_ptr(
51      new ScrollOffsetAnimationCurve(target_value, timing_function.Pass()));
52}
53
54ScrollOffsetAnimationCurve::ScrollOffsetAnimationCurve(
55    const gfx::Vector2dF& target_value,
56    scoped_ptr<TimingFunction> timing_function)
57    : target_value_(target_value), timing_function_(timing_function.Pass()) {
58}
59
60ScrollOffsetAnimationCurve::~ScrollOffsetAnimationCurve() {}
61
62void ScrollOffsetAnimationCurve::SetInitialValue(
63    const gfx::Vector2dF& initial_value) {
64  initial_value_ = initial_value;
65  total_animation_duration_ = DurationFromDelta(target_value_ - initial_value_);
66}
67
68gfx::Vector2dF ScrollOffsetAnimationCurve::GetValue(double t) const {
69  double duration = (total_animation_duration_ - last_retarget_).InSecondsF();
70  t -= last_retarget_.InSecondsF();
71
72  if (t <= 0)
73    return initial_value_;
74
75  if (t >= duration)
76    return target_value_;
77
78  double progress = (timing_function_->GetValue(t / duration));
79  return gfx::Vector2dF(gfx::Tween::FloatValueBetween(
80                            progress, initial_value_.x(), target_value_.x()),
81                        gfx::Tween::FloatValueBetween(
82                            progress, initial_value_.y(), target_value_.y()));
83}
84
85double ScrollOffsetAnimationCurve::Duration() const {
86  return total_animation_duration_.InSecondsF();
87}
88
89AnimationCurve::CurveType ScrollOffsetAnimationCurve::Type() const {
90  return ScrollOffset;
91}
92
93scoped_ptr<AnimationCurve> ScrollOffsetAnimationCurve::Clone() const {
94  scoped_ptr<TimingFunction> timing_function(
95      static_cast<TimingFunction*>(timing_function_->Clone().release()));
96  scoped_ptr<ScrollOffsetAnimationCurve> curve_clone =
97      Create(target_value_, timing_function.Pass());
98  curve_clone->initial_value_ = initial_value_;
99  curve_clone->total_animation_duration_ = total_animation_duration_;
100  curve_clone->last_retarget_ = last_retarget_;
101  return curve_clone.PassAs<AnimationCurve>();
102}
103
104void ScrollOffsetAnimationCurve::UpdateTarget(
105    double t,
106    const gfx::Vector2dF& new_target) {
107  gfx::Vector2dF current_position = GetValue(t);
108  gfx::Vector2dF old_delta = target_value_ - initial_value_;
109  gfx::Vector2dF new_delta = new_target - current_position;
110
111  double old_duration =
112      (total_animation_duration_ - last_retarget_).InSecondsF();
113  double new_duration = DurationFromDelta(new_delta).InSecondsF();
114
115  double old_velocity = timing_function_->Velocity(
116      (t - last_retarget_.InSecondsF()) / old_duration);
117
118  // TimingFunction::Velocity gives the slope of the curve from 0 to 1.
119  // To match the "true" velocity in px/sec we must adjust this slope for
120  // differences in duration and scroll delta between old and new curves.
121  double new_velocity =
122      old_velocity * (new_duration / old_duration) *
123      (MaximumDimension(old_delta) / MaximumDimension(new_delta));
124
125  initial_value_ = current_position;
126  target_value_ = new_target;
127  total_animation_duration_ = base::TimeDelta::FromSecondsD(t + new_duration);
128  last_retarget_ = base::TimeDelta::FromSecondsD(t);
129  timing_function_ = EaseOutWithInitialVelocity(new_velocity);
130}
131
132}  // namespace cc
133