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 "cc/base/time_util.h"
  13 #include "ui/gfx/animation/tween.h"
  14
  15 const double kDurationDivisor = 60.0;
  16
  17 namespace cc {
  18
  19 namespace {
  20
  21 static float MaximumDimension(const gfx::Vector2dF& delta) {
  22   return std::max(std::abs(delta.x()), std::abs(delta.y()));
  23 }
  24
  25 static base::TimeDelta DurationFromDelta(const gfx::Vector2dF& delta) {
  26   // The duration of a scroll animation depends on the size of the scroll.
  27   // The exact relationship between the size and the duration isn't specified
  28   // by the CSSOM View smooth scroll spec and is instead left up to user agents
  29   // to decide. The calculation performed here will very likely be further
  30   // tweaked before the smooth scroll API ships.
  31   return base::TimeDelta::FromMicroseconds(
  32       (std::sqrt(MaximumDimension(delta)) / kDurationDivisor) *
  33       base::Time::kMicrosecondsPerSecond);
  34 }
  35
  36 static scoped_ptr<TimingFunction> EaseOutWithInitialVelocity(double velocity) {
  37   // Based on EaseInOutTimingFunction::Create with first control point rotated.
  38   if (std::abs(velocity) < 1000.0) {
  39     const double r2 = 0.42 * 0.42;
  40     const double v2 = velocity * velocity;
  41     const double x1 = std::sqrt(r2 / (v2 + 1));
  42     const double y1 = std::sqrt(r2 * v2 / (v2 + 1));
  43     return CubicBezierTimingFunction::Create(x1, y1, 0.58, 1);
  44   }
  45
  46   // For large |velocity|, x1 approaches 0 and y1 approaches 0.42. To avoid the
  47   // risk of floating point arithmetic involving infinity and NaN, use those
  48   // values directly rather than computing them above.
  49   return CubicBezierTimingFunction::Create(0, 0.42, 0.58, 1);
  50 }
  51
  52 }  // namespace
  53
  54 scoped_ptr<ScrollOffsetAnimationCurve> ScrollOffsetAnimationCurve::Create(
  55     const gfx::ScrollOffset& target_value,
  56     scoped_ptr<TimingFunction> timing_function) {
  57   return make_scoped_ptr(
  58       new ScrollOffsetAnimationCurve(target_value, timing_function.Pass()));
  59 }
  60
  61 ScrollOffsetAnimationCurve::ScrollOffsetAnimationCurve(
  62     const gfx::ScrollOffset& target_value,
  63     scoped_ptr<TimingFunction> timing_function)
  64     : target_value_(target_value), timing_function_(timing_function.Pass()) {
  65 }
  66
  67 ScrollOffsetAnimationCurve::~ScrollOffsetAnimationCurve() {}
  68
  69 void ScrollOffsetAnimationCurve::SetInitialValue(
  70     const gfx::ScrollOffset& initial_value) {
  71   initial_value_ = initial_value;
  72   total_animation_duration_ = DurationFromDelta(
  73       target_value_.DeltaFrom(initial_value_));
  74 }
  75
  76 gfx::ScrollOffset ScrollOffsetAnimationCurve::GetValue(
  77     base::TimeDelta t) const {
  78   base::TimeDelta duration = total_animation_duration_ - last_retarget_;
  79   t -= last_retarget_;
  80
  81   if (t <= base::TimeDelta())
  82     return initial_value_;
  83
  84   if (t >= duration)
  85     return target_value_;
  86
  87   double progress = timing_function_->GetValue(TimeUtil::Divide(t, duration));
  88   return gfx::ScrollOffset(
  89       gfx::Tween::FloatValueBetween(
  90           progress, initial_value_.x(), target_value_.x()),
  91       gfx::Tween::FloatValueBetween(
  92           progress, initial_value_.y(), target_value_.y()));
  93 }
  94
  95 base::TimeDelta ScrollOffsetAnimationCurve::Duration() const {
  96   return total_animation_duration_;
  97 }
  98
  99 AnimationCurve::CurveType ScrollOffsetAnimationCurve::Type() const {
 100   return SCROLL_OFFSET;
 101 }
 102
 103 scoped_ptr<AnimationCurve> ScrollOffsetAnimationCurve::Clone() const {
 104   scoped_ptr<TimingFunction> timing_function(
 105       static_cast<TimingFunction*>(timing_function_->Clone().release()));
 106   scoped_ptr<ScrollOffsetAnimationCurve> curve_clone =
 107       Create(target_value_, timing_function.Pass());
 108   curve_clone->initial_value_ = initial_value_;
 109   curve_clone->total_animation_duration_ = total_animation_duration_;
 110   curve_clone->last_retarget_ = last_retarget_;
 111   return curve_clone.Pass();
 112 }
 113
 114 void ScrollOffsetAnimationCurve::UpdateTarget(
 115     double t,
 116     const gfx::ScrollOffset& new_target) {
 117   gfx::ScrollOffset current_position =
 118       GetValue(base::TimeDelta::FromSecondsD(t));
 119   gfx::Vector2dF old_delta = target_value_.DeltaFrom(initial_value_);
 120   gfx::Vector2dF new_delta = new_target.DeltaFrom(current_position);
 121
 122   double old_duration =
 123       (total_animation_duration_ - last_retarget_).InSecondsF();
 124   double new_duration = DurationFromDelta(new_delta).InSecondsF();
 125
 126   double old_velocity = timing_function_->Velocity(
 127       (t - last_retarget_.InSecondsF()) / old_duration);
 128
 129   // TimingFunction::Velocity gives the slope of the curve from 0 to 1.
 130   // To match the "true" velocity in px/sec we must adjust this slope for
 131   // differences in duration and scroll delta between old and new curves.
 132   double new_velocity =
 133       old_velocity * (new_duration / old_duration) *
 134       (MaximumDimension(old_delta) / MaximumDimension(new_delta));
 135
 136   initial_value_ = current_position;
 137   target_value_ = new_target;
 138   total_animation_duration_ = base::TimeDelta::FromSecondsD(t + new_duration);
 139   last_retarget_ = base::TimeDelta::FromSecondsD(t);
 140   timing_function_ = EaseOutWithInitialVelocity(new_velocity);
 141 }
 142
 143 }  // namespace cc