Scroll offset animation curve retargeting.

Adds support for updating the target of an in-progress input-triggered impl-side scroll offset animation, keeping the velocity function continuous.

BUG=575

Review URL: https://codereview.chromium.org/393713002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@284228 0039d316-1c4b-4281-b951-d872f2087c98

7 files changed, 133 insertions, 22 deletions

diff --git a/cc/animation/scroll_offset_animation_curve.cc b/cc/animation/scroll_offset_animation_curve.cc
index a7283b8..8211a95 100644
--- a/cc/animation/scroll_offset_animation_curve.cc
+++ b/cc/animation/scroll_offset_animation_curve.cc
@@ -15,6 +15,35 @@ const double kDurationDivisor = 60.0;
 
 namespace cc {
 
+namespace {
+
+static float MaximumDimension(gfx::Vector2dF delta) {
+  return std::max(std::abs(delta.x()), std::abs(delta.y()));
+}
+
+static base::TimeDelta DurationFromDelta(gfx::Vector2dF delta) {
+  // The duration of a scroll animation depends on the size of the scroll.
+  // The exact relationship between the size and the duration isn't specified
+  // by the CSSOM View smooth scroll spec and is instead left up to user agents
+  // to decide. The calculation performed here will very likely be further
+  // tweaked before the smooth scroll API ships.
+  return base::TimeDelta::FromMicroseconds(
+      (std::sqrt(MaximumDimension(delta)) / kDurationDivisor) *
+      base::Time::kMicrosecondsPerSecond);
+}
+
+static scoped_ptr<TimingFunction> EaseOutWithInitialVelocity(double velocity) {
+  // Based on EaseInOutTimingFunction::Create with first control point rotated.
+  const double r2 = 0.42 * 0.42;
+  const double v2 = velocity * velocity;
+  const double x1 = std::sqrt(r2 / (v2 + 1));
+  const double y1 = std::sqrt(r2 * v2 / (v2 + 1));
+  return CubicBezierTimingFunction::Create(x1, y1, 0.58, 1)
+      .PassAs<TimingFunction>();
+}
+
+}  // namespace
+
 scoped_ptr<ScrollOffsetAnimationCurve> ScrollOffsetAnimationCurve::Create(
     const gfx::Vector2dF& target_value,
     scoped_ptr<TimingFunction> timing_function) {
@@ -33,22 +62,12 @@ ScrollOffsetAnimationCurve::~ScrollOffsetAnimationCurve() {}
 void ScrollOffsetAnimationCurve::SetInitialValue(
     const gfx::Vector2dF& initial_value) {
   initial_value_ = initial_value;
-
-  // The duration of a scroll animation depends on the size of the scroll.
-  // The exact relationship between the size and the duration isn't specified
-  // by the CSSOM View smooth scroll spec and is instead left up to user agents
-  // to decide. The calculation performed here will very likely be further
-  // tweaked before the smooth scroll API ships.
-  float delta_x = std::abs(target_value_.x() - initial_value_.x());
-  float delta_y = std::abs(target_value_.y() - initial_value_.y());
-  float max_delta = std::max(delta_x, delta_y);
-  duration_ = base::TimeDelta::FromMicroseconds(
-      (std::sqrt(max_delta) / kDurationDivisor) *
-      base::Time::kMicrosecondsPerSecond);
+  total_animation_duration_ = DurationFromDelta(target_value_ - initial_value_);
 }
 
 gfx::Vector2dF ScrollOffsetAnimationCurve::GetValue(double t) const {
-  double duration = duration_.InSecondsF();
+  double duration = (total_animation_duration_ - last_retarget_).InSecondsF();
+  t -= last_retarget_.InSecondsF();
 
   if (t <= 0)
     return initial_value_;
@@ -64,7 +83,7 @@ gfx::Vector2dF ScrollOffsetAnimationCurve::GetValue(double t) const {
 }
 
 double ScrollOffsetAnimationCurve::Duration() const {
-  return duration_.InSecondsF();
+  return total_animation_duration_.InSecondsF();
 }
 
 AnimationCurve::CurveType ScrollOffsetAnimationCurve::Type() const {
@@ -77,8 +96,37 @@ scoped_ptr<AnimationCurve> ScrollOffsetAnimationCurve::Clone() const {
   scoped_ptr<ScrollOffsetAnimationCurve> curve_clone =
       Create(target_value_, timing_function.Pass());
   curve_clone->initial_value_ = initial_value_;
-  curve_clone->duration_ = duration_;
+  curve_clone->total_animation_duration_ = total_animation_duration_;
+  curve_clone->last_retarget_ = last_retarget_;
   return curve_clone.PassAs<AnimationCurve>();
 }
 
+void ScrollOffsetAnimationCurve::UpdateTarget(
+    double t,
+    const gfx::Vector2dF& new_target) {
+  gfx::Vector2dF current_position = GetValue(t);
+  gfx::Vector2dF old_delta = target_value_ - initial_value_;
+  gfx::Vector2dF new_delta = new_target - current_position;
+
+  double old_duration =
+      (total_animation_duration_ - last_retarget_).InSecondsF();
+  double new_duration = DurationFromDelta(new_delta).InSecondsF();
+
+  double old_velocity = timing_function_->Velocity(
+      (t - last_retarget_.InSecondsF()) / old_duration);
+
+  // TimingFunction::Velocity gives the slope of the curve from 0 to 1.
+  // To match the "true" velocity in px/sec we must adjust this slope for
+  // differences in duration and scroll delta between old and new curves.
+  double new_velocity =
+      old_velocity * (new_duration / old_duration) *
+      (MaximumDimension(old_delta) / MaximumDimension(new_delta));
+
+  initial_value_ = current_position;
+  target_value_ = new_target;
+  total_animation_duration_ = base::TimeDelta::FromSecondsD(t + new_duration);
+  last_retarget_ = base::TimeDelta::FromSecondsD(t);
+  timing_function_ = EaseOutWithInitialVelocity(new_velocity);
+}
+
 }  // namespace cc
diff --git a/cc/animation/scroll_offset_animation_curve.h b/cc/animation/scroll_offset_animation_curve.h
index 543ae37..3d71e13 100644
--- a/cc/animation/scroll_offset_animation_curve.h
+++ b/cc/animation/scroll_offset_animation_curve.h
@@ -24,6 +24,8 @@ class CC_EXPORT ScrollOffsetAnimationCurve : public AnimationCurve {
 
   void SetInitialValue(const gfx::Vector2dF& initial_value);
   gfx::Vector2dF GetValue(double t) const;
+  gfx::Vector2dF target_value() const { return target_value_; }
+  void UpdateTarget(double t, const gfx::Vector2dF& new_target);
 
   // AnimationCurve implementation
   virtual double Duration() const OVERRIDE;
@@ -36,7 +38,10 @@ class CC_EXPORT ScrollOffsetAnimationCurve : public AnimationCurve {
 
   gfx::Vector2dF initial_value_;
   gfx::Vector2dF target_value_;
-  base::TimeDelta duration_;
+  base::TimeDelta total_animation_duration_;
+
+  // Time from animation start to most recent UpdateTarget.
+  base::TimeDelta last_retarget_;
 
   scoped_ptr<TimingFunction> timing_function_;
 
diff --git a/cc/animation/scroll_offset_animation_curve_unittest.cc b/cc/animation/scroll_offset_animation_curve_unittest.cc
index 63445d9..1b8fdb5 100644
--- a/cc/animation/scroll_offset_animation_curve_unittest.cc
+++ b/cc/animation/scroll_offset_animation_curve_unittest.cc
@@ -119,5 +119,30 @@ TEST(ScrollOffsetAnimationCurveTest, Clone) {
   EXPECT_NEAR(37.4168f, value.y(), 0.00015f);
 }
 
+TEST(ScrollOffsetAnimationCurveTest, UpdateTarget) {
+  gfx::Vector2dF initial_value(0.f, 0.f);
+  gfx::Vector2dF target_value(0.f, 3600.f);
+  scoped_ptr<ScrollOffsetAnimationCurve> curve(
+      ScrollOffsetAnimationCurve::Create(
+          target_value, EaseInOutTimingFunction::Create().Pass()));
+  curve->SetInitialValue(initial_value);
+  EXPECT_EQ(1.0, curve->Duration());
+  EXPECT_EQ(1800.0, curve->GetValue(0.5).y());
+  EXPECT_EQ(3600.0, curve->GetValue(1.0).y());
+
+  curve->UpdateTarget(0.5, gfx::Vector2dF(0.0, 9900.0));
+
+  EXPECT_EQ(2.0, curve->Duration());
+  EXPECT_EQ(1800.0, curve->GetValue(0.5).y());
+  EXPECT_NEAR(5566.49, curve->GetValue(1.0).y(), 0.01);
+  EXPECT_EQ(9900.0, curve->GetValue(2.0).y());
+
+  curve->UpdateTarget(1.0, gfx::Vector2dF(0.0, 7200.0));
+
+  EXPECT_NEAR(1.674, curve->Duration(), 0.01);
+  EXPECT_NEAR(5566.49, curve->GetValue(1.0).y(), 0.01);
+  EXPECT_EQ(7200.0, curve->GetValue(1.674).y());
+}
+
 }  // namespace
 }  // namespace cc
diff --git a/cc/animation/timing_function.cc b/cc/animation/timing_function.cc
index bf11c20..71319e1 100644
--- a/cc/animation/timing_function.cc
+++ b/cc/animation/timing_function.cc
@@ -45,6 +45,10 @@ void CubicBezierTimingFunction::Range(float* min, float* max) const {
   *max = static_cast<float>(max_d);
 }
 
+float CubicBezierTimingFunction::Velocity(double x) const {
+  return static_cast<float>(bezier_.Slope(x));
+}
+
 // These numbers come from
 // http://www.w3.org/TR/css3-transitions/#transition-timing-function_tag.
 scoped_ptr<TimingFunction> EaseTimingFunction::Create() {
diff --git a/cc/animation/timing_function.h b/cc/animation/timing_function.h
index 647701f..cc97939 100644
--- a/cc/animation/timing_function.h
+++ b/cc/animation/timing_function.h
@@ -22,6 +22,7 @@ class CC_EXPORT TimingFunction : public FloatAnimationCurve {
   // The smallest and largest values returned by GetValue for inputs in
   // [0, 1].
   virtual void Range(float* min, float* max) const = 0;
+  virtual float Velocity(double time) const = 0;
 
  protected:
   TimingFunction();
@@ -41,6 +42,7 @@ class CC_EXPORT CubicBezierTimingFunction : public TimingFunction {
   virtual scoped_ptr<AnimationCurve> Clone() const OVERRIDE;
 
   virtual void Range(float* min, float* max) const OVERRIDE;
+  virtual float Velocity(double time) const OVERRIDE;
 
  protected:
   CubicBezierTimingFunction(double x1, double y1, double x2, double y2);
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index a2c8111..f137cb4 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -2302,9 +2302,25 @@ InputHandler::ScrollStatus LayerTreeHostImpl::ScrollBegin(
 InputHandler::ScrollStatus LayerTreeHostImpl::ScrollAnimated(
     const gfx::Point& viewport_point,
     const gfx::Vector2dF& scroll_delta) {
-  if (CurrentlyScrollingLayer()) {
-    // TODO(skobes): Update the target of the existing animation.
-    return ScrollIgnored;
+  if (LayerImpl* layer_impl = CurrentlyScrollingLayer()) {
+    Animation* animation =
+        layer_impl->layer_animation_controller()->GetAnimation(
+            Animation::ScrollOffset);
+    if (!animation)
+      return ScrollIgnored;
+
+    ScrollOffsetAnimationCurve* curve =
+        animation->curve()->ToScrollOffsetAnimationCurve();
+
+    gfx::Vector2dF new_target = curve->target_value() + scroll_delta;
+    new_target.SetToMax(gfx::Vector2dF());
+    new_target.SetToMin(layer_impl->MaxScrollOffset());
+
+    curve->UpdateTarget(
+        animation->TrimTimeToCurrentIteration(CurrentFrameTimeTicks()),
+        new_target);
+
+    return ScrollStarted;
   }
   // ScrollAnimated is only used for wheel scrolls. We use the same bubbling
   // behavior as ScrollBy to determine which layer to animate, but we do not
@@ -2341,7 +2357,7 @@ InputHandler::ScrollStatus LayerTreeHostImpl::ScrollAnimated(
       curve->SetInitialValue(current_offset);
 
       scoped_ptr<Animation> animation =
-          Animation::Create(curve->Clone().Pass(),
+          Animation::Create(curve.PassAs<AnimationCurve>(),
                             AnimationIdProvider::NextAnimationId(),
                             AnimationIdProvider::NextGroupId(),
                             Animation::ScrollOffset);
diff --git a/cc/trees/layer_tree_host_impl_unittest.cc b/cc/trees/layer_tree_host_impl_unittest.cc
index 05fc478..d05a493 100644
--- a/cc/trees/layer_tree_host_impl_unittest.cc
+++ b/cc/trees/layer_tree_host_impl_unittest.cc
@@ -6670,7 +6670,7 @@ TEST_F(LayerTreeHostImplTest, ExternalTransformReflectedInNextDraw) {
 }
 
 TEST_F(LayerTreeHostImplTest, ScrollAnimated) {
-  SetupScrollAndContentsLayers(gfx::Size(100, 100));
+  SetupScrollAndContentsLayers(gfx::Size(100, 150));
   host_impl_->SetViewportSize(gfx::Size(50, 50));
   DrawFrame();
 
@@ -6693,10 +6693,21 @@ TEST_F(LayerTreeHostImplTest, ScrollAnimated) {
   float y = scrolling_layer->TotalScrollOffset().y();
   EXPECT_TRUE(y > 1 && y < 49);
 
+  // Update target.
+  EXPECT_EQ(InputHandler::ScrollStarted,
+            host_impl_->ScrollAnimated(gfx::Point(), gfx::Vector2d(0, 50)));
+
   host_impl_->Animate(start_time + base::TimeDelta::FromMilliseconds(200));
   host_impl_->UpdateAnimationState(true);
 
-  EXPECT_EQ(gfx::Vector2dF(0, 50), scrolling_layer->TotalScrollOffset());
+  y = scrolling_layer->TotalScrollOffset().y();
+  EXPECT_TRUE(y > 50 && y < 100);
+  EXPECT_EQ(scrolling_layer, host_impl_->CurrentlyScrollingLayer());
+
+  host_impl_->Animate(start_time + base::TimeDelta::FromMilliseconds(250));
+  host_impl_->UpdateAnimationState(true);
+
+  EXPECT_EQ(gfx::Vector2dF(0, 100), scrolling_layer->TotalScrollOffset());
   EXPECT_EQ(NULL, host_impl_->CurrentlyScrollingLayer());
 }