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       .PassAs<TimingFunction>();
  43 }
  44
  45 }  // namespace
  46
  47 scoped_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
  54 ScrollOffsetAnimationCurve::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
  60 ScrollOffsetAnimationCurve::~ScrollOffsetAnimationCurve() {}
  61
  62 void ScrollOffsetAnimationCurve::SetInitialValue(
  63     const gfx::Vector2dF& initial_value) {
  64   initial_value_ = initial_value;
  65   total_animation_duration_ = DurationFromDelta(target_value_ - initial_value_);
  66 }
  67
  68 gfx::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
  85 double ScrollOffsetAnimationCurve::Duration() const {
  86   return total_animation_duration_.InSecondsF();
  87 }
  88
  89 AnimationCurve::CurveType ScrollOffsetAnimationCurve::Type() const {
  90   return ScrollOffset;
  91 }
  92
  93 scoped_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
 104 void 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