cc : Split TransformTree::ComputeTransform

cc/trees/property_tree.h

Index: cc/trees/property_tree.h
diff --git a/cc/trees/property_tree.h b/cc/trees/property_tree.h
index 396c4cf30f68eebc5b18fdef8651495a3b17cae2..17040a8ed35237c0e28ec1965634d261151843ad 100644
--- a/cc/trees/property_tree.h
+++ b/cc/trees/property_tree.h
@@ -154,6 +154,10 @@ class CC_EXPORT TransformTree final : public PropertyTree<TransformNode> {
                         int dest_id,
                         gfx::Transform* transform) const;
 
+  bool ComputeTransformFromSourceToParent(int source_id,
+                                          int dest_id,
+                                          gfx::Transform* transform) const;

[ajuma, 2016/07/27 15:57:11]

It'd be good if there was some way to enforce that this is used only for
source-to-parent transforms rather than arbitrary transforms. One idea: rename
this ComputeTranslation() with a comment that this can only be called between
pairs of nodes where the transform between nodes is a 2d translation, and then
DCHECK that the computed transform is indeed a 2d translation before returning?

[jaydasika, 2016/07/27 18:42:23]

Done.

+
   void ResetChangeTracking();
   // Updates the parent, target, and screen space transforms and snapping.
   void UpdateTransforms(int id);
@@ -245,10 +249,9 @@ class CC_EXPORT TransformTree final : public PropertyTree<TransformNode> {
   void FromProtobuf(const proto::PropertyTree& proto,
                     std::unordered_map<int, int>* node_id_to_index_map);
 
-  // Computes the combined transform between |source_id| and |dest_id| and
-  // returns false if the inverse of a singular transform was used. These two
-  // nodes must be on the same ancestor chain.
-  bool CombineTransformsBetween(int source_id,
+  // Computes the combined transform between |source_id| and |dest_id|. These
+  // two nodes must be on the same ancestor chain.
+  void CombineTransformsBetween(int source_id,
                                 int dest_id,
                                 gfx::Transform* transform) const;
 
@@ -591,6 +594,10 @@ class CC_EXPORT PropertyTrees final {
                                 int effect_id,
                                 gfx::Transform* transform) const;
 
+  bool ComputeTransformFromTarget(int transform_id,
+                                  int effect_id,
+                                  gfx::Transform* transform) const;
+
  private:
   gfx::Vector2dF inner_viewport_container_bounds_delta_;
   gfx::Vector2dF outer_viewport_container_bounds_delta_;