Add support for inverse transform animations.

ui/compositor/layer_animation_element.cc

Index: ui/compositor/layer_animation_element.cc
diff --git a/ui/compositor/layer_animation_element.cc b/ui/compositor/layer_animation_element.cc
index f70c1084a1db9e134227c54e7a883c83fc2e6433..d1b2b1cb05e566a026050c3ccd861f1b951be4a8 100644
--- a/ui/compositor/layer_animation_element.cc
+++ b/ui/compositor/layer_animation_element.cc
@@ -563,6 +563,108 @@ class ThreadedTransformTransition : public ThreadedLayerAnimationElement {
   DISALLOW_COPY_AND_ASSIGN(ThreadedTransformTransition);
 };
 
+// ChildCounterTransformTransition ---------------------------------------------
+
+class ChildCounterTransformTransition : public ThreadedLayerAnimationElement {
+ public:
+  ChildCounterTransformTransition(const gfx::Transform& parent_start,
+                                  const gfx::Transform& parent_target,
+                                  base::TimeDelta duration)
+      : ThreadedLayerAnimationElement(GetProperties(), duration),
+        parent_start_(parent_start),
+        parent_target_(parent_target) {
+  }
+  virtual ~ChildCounterTransformTransition() {}
+
+ protected:
+  virtual void OnStart(LayerAnimationDelegate* delegate) OVERRIDE {
+    start_ = delegate->GetTransformForAnimation();
+    effective_start_ = start_ * parent_start_;
+    float device_scale_factor = delegate->GetDeviceScaleFactor();
+    cc_start_ = Layer::ConvertTransformToCCTransform(start_,
+                                                     device_scale_factor);
+    cc_effective_start_ = Layer::ConvertTransformToCCTransform(
+        effective_start_,
+        device_scale_factor);
+    cc_parent_start_ = Layer::ConvertTransformToCCTransform(
+        parent_start_,
+        device_scale_factor);
+    cc_parent_target_ = Layer::ConvertTransformToCCTransform(
+        parent_target_,
+        device_scale_factor);
+  }
+
+  virtual void OnAbort(LayerAnimationDelegate* delegate) OVERRIDE {
+    if (delegate && Started()) {
+      ThreadedLayerAnimationElement::OnAbort(delegate);
+      delegate->SetTransformFromAnimation(ComputeCurrentTransform());
+    }
+  }
+
+  virtual void OnEnd(LayerAnimationDelegate* delegate) OVERRIDE {
+    delegate->SetTransformFromAnimation(
+        ComputeWithParentTransform(start_, parent_target_));
+  }
+
+  virtual scoped_ptr<cc::Animation> CreateCCAnimation() OVERRIDE {
+    gfx::Transform target = ComputeWithParentTransform(cc_effective_start_,
+                                                       cc_parent_target_);
+    scoped_ptr<cc::AnimationCurve> animation_curve(
+        new TransformAnimationCurveAdapter(tween_type(),

[ajuma, 2013/08/20 15:32:41]

I think we'll to perform matrix inversion in the curve's GetValue method,
meaning we'll either need to add an additional argument to
TransformAnimationCurveAdapter's constructor, or (more likely) we'll need a new
kind of TransformAnimationCurveAdapter.

[avallee, 2013/08/22 22:21:59]

Done.

+                                           cc_start_,
+                                           target,
+                                           duration()));
+    scoped_ptr<cc::Animation> animation(
+        cc::Animation::Create(animation_curve.Pass(),
+                              animation_id(),
+                              animation_group_id(),
+                              cc::Animation::Transform));
+    return animation.Pass();
+  }
+
+  virtual void OnGetTarget(TargetValue* target) const OVERRIDE {
+    target->transform = ComputeWithParentTransform(start_, parent_target_);

[ajuma, 2013/08/20 15:32:41]

If ComputeWithParentTransform turns out to be more complex than, say, a matrix
multiplication, we should store the target value to avoid having to recompute it
each time this gets called.

[avallee, 2013/08/22 22:21:59]

I'll leave this here for now. We could compute the target_ value in OnStart once
if this turns out to be called frequently.

+  }
+
+ private:
+  gfx::Transform ComputeCurrentTransform() const {
+    gfx::Transform parent_current = Tween::ValueBetween(
+        Tween::CalculateValue(tween_type(), last_progressed_fraction()),
+        parent_start_,
+        parent_target_);
+    return ComputeWithParentTransform(effective_start_, parent_current);
+  }
+
+  gfx::Transform ComputeWithParentTransform(gfx::Transform start,
+                                            gfx::Transform parent) const {
+    gfx::Transform to_return(gfx::Transform::kSkipInitialization);
+    if (!parent.GetInverse(&to_return)) {
+      DLOG(WARNING) << "Parent transform not invertible.";

[ajuma, 2013/08/20 15:32:41]

Use a DCHECK instead of a DLOG (so that we crash a debug build instead of
providing output that might not be noticed).

[avallee, 2013/08/22 22:21:59]

Done.

+      to_return.MakeIdentity();
+    }
+    to_return.ConcatTransform(start);

[ajuma, 2013/08/20 15:32:41]

Since we're skipping initialization above, this is concatenating with an
uninitialized transform.

[avallee, 2013/08/22 22:21:59]

It's initialized either by successfully getting the inverse of parent or by
MakeIdentity in the failure case.

+    return to_return;

[ajuma, 2013/08/20 15:32:41]

This method isn't using |parent| anywhere. Is something missing?

[avallee, 2013/08/22 22:21:59]

parent.GetInverse inside the if statement.

+  }
+
+  static AnimatableProperties GetProperties() {
+    AnimatableProperties properties;
+    properties.insert(LayerAnimationElement::TRANSFORM);
+    return properties;
+  }
+
+  gfx::Transform start_;
+  gfx::Transform cc_start_;
+  gfx::Transform effective_start_;
+  gfx::Transform cc_effective_start_;
+
+  const gfx::Transform parent_start_;
+  gfx::Transform cc_parent_start_;
+  const gfx::Transform parent_target_;
+  gfx::Transform cc_parent_target_;
+
+  DISALLOW_COPY_AND_ASSIGN(ChildCounterTransformTransition);
+};
+
 }  // namespace
 
 // LayerAnimationElement::TargetValue ------------------------------------------
@@ -729,6 +831,16 @@ LayerAnimationElement* LayerAnimationElement::CreateTransformElement(
 }
 
 // static
+LayerAnimationElement* LayerAnimationElement::CreateInverseTransformElement(
+    const gfx::Transform& parent_start,
+    const gfx::Transform& parent_end,
+    base::TimeDelta duration) {
+  return new ChildCounterTransformTransition(parent_start,
+                                             parent_end,
+                                             duration);
+}
+
+// static
 LayerAnimationElement*
 LayerAnimationElement::CreateInterpolatedTransformElement(
     InterpolatedTransform* interpolated_transform,