cc: Support animating scroll offset

cc/animation/scroll_offset_animation_curve.cc

Index: cc/animation/scroll_offset_animation_curve.cc
diff --git a/cc/animation/scroll_offset_animation_curve.cc b/cc/animation/scroll_offset_animation_curve.cc
index d5cfd1c2df0fe147bed0914ec59a17b295338a40..24a43cff7a4cf4720cb5c3a643921aaa8f60d193 100644
--- a/cc/animation/scroll_offset_animation_curve.cc
+++ b/cc/animation/scroll_offset_animation_curve.cc
@@ -4,10 +4,15 @@
 
 #include "cc/animation/scroll_offset_animation_curve.h"
 
+#include <algorithm>
+#include <cmath>
+
 #include "base/logging.h"
 #include "cc/animation/timing_function.h"
 #include "ui/gfx/animation/tween.h"
 
+const double kDurationDivisor = 60.0;
+
 namespace cc {
 
 scoped_ptr<ScrollOffsetAnimationCurve> ScrollOffsetAnimationCurve::Create(
@@ -26,6 +31,14 @@ ScrollOffsetAnimationCurve::ScrollOffsetAnimationCurve(
 
 ScrollOffsetAnimationCurve::~ScrollOffsetAnimationCurve() {}
 
+void ScrollOffsetAnimationCurve::SetInitialValue(gfx::Vector2dF initial_value) {
+  initial_value_ = initial_value;
+  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_ = std::sqrt(max_delta)/kDurationDivisor;

[ajuma, 2013/11/29 15:14:06]

This calculation will almost certainly be tweaked before we ship the smooth
scroll API. For now, we just need *some* reasonable duration calculation here.

[Ian Vollick, 2013/11/29 15:29:29]

Please add a comment here explaining that this math is just a tweak to get the
right feel (and might need to be updated). At first I was wondering if there was
a geometrical reason for the sqrt..

[ajuma, 2013/11/29 21:18:41]

Done. (The reason for the sqrt is just so that the duration grows more slowly
than the size.)

+}
+
 gfx::Vector2dF ScrollOffsetAnimationCurve::GetValue(double t) const {
   if (t <= 0)
     return initial_value_;
@@ -53,8 +66,8 @@ scoped_ptr<AnimationCurve> ScrollOffsetAnimationCurve::Clone() const {
       static_cast<TimingFunction*>(timing_function_->Clone().release()));
   scoped_ptr<ScrollOffsetAnimationCurve> curve_clone =
       Create(target_value_, timing_function.Pass());
-  curve_clone->set_initial_value(initial_value_);
-  curve_clone->set_duration(duration_);
+  curve_clone->initial_value_ = initial_value_;
+  curve_clone->duration_ = duration_;
   return curve_clone.PassAs<AnimationCurve>();
 }