cc: Compute transform to target using effect id.

cc/trees/property_tree.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stddef.h>
 
 #include <set>
 #include <vector>
 
 #include "base/logging.h"
@@ skipping 755 matching lines @@
     TransformNode* transform_node = transform_tree.Node(node->transform_id);
     if (transform_node->is_invertible &&
         transform_node->ancestors_are_invertible) {
       if (transform_node->sorting_context_id) {
         const TransformNode* parent_transform_node =
             transform_tree.parent(transform_node);
         if (parent_transform_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 {
           node->hidden_by_backface_visibility =
               transform_node->local.IsBackFaceVisible();
         }
         return;
       }
     }
   }
@@ skipping 1080 matching lines @@
   gfx::Transform screen_space_transform = transform_tree.ToScreen(transform_id);
   const EffectNode* effect_node = effect_tree.Node(effect_id);
 
   if (effect_node->surface_contents_scale.x() != 0.0 &&
       effect_node->surface_contents_scale.y() != 0.0)
     screen_space_transform.Scale(1.0 / effect_node->surface_contents_scale.x(),
                                  1.0 / effect_node->surface_contents_scale.y());
   return screen_space_transform;
 }
 
+bool PropertyTrees::ComputeTransformToTarget(int transform_id,
+                                             int effect_id,
+                                             gfx::Transform* transform) const {
+  transform->MakeIdentity();
+  const EffectNode* effect_node = effect_tree.Node(effect_id);
+
+  DCHECK(effect_node->has_render_surface || effect_node->id == 0);
+
+  if (transform_id == effect_node->transform_id)
+    return true;
+
+  if (transform_id > effect_node->transform_id) {
+    return transform_tree.CombineTransformsBetween(
+        transform_id, effect_node->transform_id, transform);
+  }
+
+  return transform_tree.CombineInversesBetween(
+      transform_id, effect_node->transform_id, transform);

[ajuma, 2016/07/22 13:45:38]

Do we also need to handle the case where the two transform nodes don't have an
ancestor-descendant relationship? See
https://cs.chromium.org/chromium/src/cc/trees/property_tree.cc?rcl=0&l=260 for
an example.

[jaydasika, 2016/07/22 15:59:52]

This function calls CombineTransforms(/Inverses)Between which handles it.

+}
+
 }  // namespace cc