cc/animation/scroll_offset_animation_curve.cc

   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
  14 const double kDurationDivisor = 60.0;
  15
  16 namespace cc {
  17
  18 namespace {
  19
  20 static float MaximumDimension(gfx::Vector2dF delta) {
  21   return std::max(std::abs(delta.x()), std::abs(delta.y()));
  22 }
  23
  24 static 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
  35 static 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 }
  43
  44 }  // namespace
  45
  46 scoped_ptr<ScrollOffsetAnimationCurve> ScrollOffsetAnimationCurve::Create(
  47     const gfx::ScrollOffset& target_value,
  48     scoped_ptr<TimingFunction> timing_function) {
  49   return make_scoped_ptr(
  50       new ScrollOffsetAnimationCurve(target_value, timing_function.Pass()));
  51 }
  52
  53 ScrollOffsetAnimationCurve::ScrollOffsetAnimationCurve(
  54     const gfx::ScrollOffset& target_value,
  55     scoped_ptr<TimingFunction> timing_function)
  56     : target_value_(target_value), timing_function_(timing_function.Pass()) {
  57 }
  58
  59 ScrollOffsetAnimationCurve::~ScrollOffsetAnimationCurve() {}
  60
  61 void ScrollOffsetAnimationCurve::SetInitialValue(
  62     const gfx::ScrollOffset& initial_value) {
  63   initial_value_ = initial_value;
  64   total_animation_duration_ = DurationFromDelta(
  65       target_value_.DeltaFrom(initial_value_));
  66 }
  67
  68 gfx::ScrollOffset 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::ScrollOffset(
  80       gfx::Tween::FloatValueBetween(
  81           progress, initial_value_.x(), target_value_.x()),
  82       gfx::Tween::FloatValueBetween(
  83           progress, initial_value_.y(), target_value_.y()));
  84 }
  85
  86 base::TimeDelta ScrollOffsetAnimationCurve::Duration() const {
  87   return total_animation_duration_;
  88 }
  89
  90 AnimationCurve::CurveType ScrollOffsetAnimationCurve::Type() const {
  91   return ScrollOffset;
  92 }
  93
  94 scoped_ptr<AnimationCurve> ScrollOffsetAnimationCurve::Clone() const {
  95   scoped_ptr<TimingFunction> timing_function(
  96       static_cast<TimingFunction*>(timing_function_->Clone().release()));
  97   scoped_ptr<ScrollOffsetAnimationCurve> curve_clone =
  98       Create(target_value_, timing_function.Pass());
  99   curve_clone->initial_value_ = initial_value_;
 100   curve_clone->total_animation_duration_ = total_animation_duration_;
 101   curve_clone->last_retarget_ = last_retarget_;
 102   return curve_clone.Pass();
 103 }
 104
 105 void ScrollOffsetAnimationCurve::UpdateTarget(
 106     double t,
 107     const gfx::ScrollOffset& new_target) {
 108   gfx::ScrollOffset current_position = GetValue(t);
 109   gfx::Vector2dF old_delta = target_value_.DeltaFrom(initial_value_);
 110   gfx::Vector2dF new_delta = new_target.DeltaFrom(current_position);
 111
 112   double old_duration =
 113       (total_animation_duration_ - last_retarget_).InSecondsF();
 114   double new_duration = DurationFromDelta(new_delta).InSecondsF();
 115
 116   double old_velocity = timing_function_->Velocity(
 117       (t - last_retarget_.InSecondsF()) / old_duration);
 118
 119   // TimingFunction::Velocity gives the slope of the curve from 0 to 1.
 120   // To match the "true" velocity in px/sec we must adjust this slope for
 121   // differences in duration and scroll delta between old and new curves.
 122   double new_velocity =
 123       old_velocity * (new_duration / old_duration) *
 124       (MaximumDimension(old_delta) / MaximumDimension(new_delta));
 125
 126   initial_value_ = current_position;
 127   target_value_ = new_target;
 128   total_animation_duration_ = base::TimeDelta::FromSecondsD(t + new_duration);
 129   last_retarget_ = base::TimeDelta::FromSecondsD(t);
 130   timing_function_ = EaseOutWithInitialVelocity(new_velocity);
 131 }
 132
 133 }  // namespace cc