cc: Compute transform to target using effect id.

This CL adds ComputeTransformsToTarget method which takes a transform id
and effect id and calls this instead of ComputeTransforms when
destination is target.

BUG=622372
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_blink_rel

Review-Url: https://codereview.chromium.org/2172003002
Cr-Commit-Position: refs/heads/master@{#407282}

cc/trees/layer_tree_impl.cc

@@ -1001,9 +1001,9 @@ bool LayerTreeImpl::UpdateDrawProperties(bool update_lcd_text) {
           // We are calculating transform between two render surfaces. So, we
           // need to apply the surface contents scale at target and remove the
           // surface contents scale at source.
-          property_trees()->transform_tree.ComputeTransform(
+          property_trees()->ComputeTransformToTarget(
               it->render_surface()->TransformTreeIndex(),
-              occlusion_surface->TransformTreeIndex(), &draw_transform);
+              occlusion_surface->EffectTreeIndex(), &draw_transform);
           // We don't have to apply surface contents scale when target is root.
           if (occlusion_surface->TransformTreeIndex() != 0) {
             const EffectNode* occlusion_effect_node =

cc/trees/property_tree.cc

@@ -773,9 +773,8 @@ void EffectTree::UpdateBackfaceVisibility(EffectNode* node,
             parent_transform_node->sorting_context_id ==
                 transform_node->sorting_context_id) {
           gfx::Transform surface_draw_transform;
-          transform_tree.ComputeTransform(
-              transform_node->id, transform_tree.TargetId(transform_node->id),
-              &surface_draw_transform);
+          property_trees()->ComputeTransformToTarget(
+              transform_node->id, node->target_id, &surface_draw_transform);
           node->hidden_by_backface_visibility =
               surface_draw_transform.IsBackFaceVisible();
         } else {
@@ -1876,4 +1875,33 @@ gfx::Transform PropertyTrees::ToScreenSpaceTransformWithoutSurfaceContentsScale(
   return screen_space_transform;
 }
 
+bool PropertyTrees::ComputeTransformToTarget(int transform_id,
+                                             int effect_id,
+                                             gfx::Transform* transform) const {
+  transform->MakeIdentity();
+
+  int destination_transform_id;
+  if (effect_id == -1) {
+    // This can happen when PaintArtifactCompositor builds property trees as
+    // it doesn't set effect ids on clip nodes. We want to compute transform
+    // to the root in this case.
+    destination_transform_id = 0;
+  } else {
+    const EffectNode* effect_node = effect_tree.Node(effect_id);
+    DCHECK(effect_node->has_render_surface || effect_node->id == 0);
+    destination_transform_id = effect_node->transform_id;
+  }
+
+  if (transform_id == destination_transform_id)
+    return true;
+
+  if (transform_id > destination_transform_id) {
+    return transform_tree.CombineTransformsBetween(
+        transform_id, destination_transform_id, transform);
+  }
+
+  return transform_tree.CombineInversesBetween(
+      transform_id, destination_transform_id, transform);
+}
+
 }  // namespace cc

cc/trees/property_tree.h

@@ -237,11 +237,6 @@ class CC_EXPORT TransformTree final : public PropertyTree<TransformNode> {
   void FromProtobuf(const proto::PropertyTree& proto,
                     std::unordered_map<int, int>* node_id_to_index_map);
 
- private:
-  // Returns true iff the node at |desc_id| is a descendant of the node at
-  // |anc_id|.
-  bool IsDescendant(int desc_id, int anc_id) const;
-
   // 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.
@@ -256,6 +251,11 @@ class CC_EXPORT TransformTree final : public PropertyTree<TransformNode> {
                               int dest_id,
                               gfx::Transform* transform) const;
 
+ private:
+  // Returns true iff the node at |desc_id| is a descendant of the node at
+  // |anc_id|.
+  bool IsDescendant(int desc_id, int anc_id) const;
+
   void UpdateLocalTransform(TransformNode* node);
   void UpdateScreenSpaceTransform(TransformNode* node,
                                   TransformNode* parent_node,
@@ -544,6 +544,9 @@ class CC_EXPORT PropertyTrees final {
   gfx::Transform ToScreenSpaceTransformWithoutSurfaceContentsScale(
       int transform_id,
       int effect_id) const;
+  bool ComputeTransformToTarget(int transform_id,
+                                int effect_id,
+                                gfx::Transform* transform) const;
 
  private:
   gfx::Vector2dF inner_viewport_container_bounds_delta_;