Build mapping from element id to transform/effect nodes.

cc/trees/property_tree.h

 // 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.
 
 #ifndef CC_TREES_PROPERTY_TREE_H_
 #define CC_TREES_PROPERTY_TREE_H_
 
 #include <stddef.h>
 
 #include <memory>
@@ skipping 509 matching lines @@
 
 class CC_EXPORT PropertyTrees final {
  public:
   PropertyTrees();
   PropertyTrees(const PropertyTrees& other) = delete;
   ~PropertyTrees();
 
   bool operator==(const PropertyTrees& other) const;
   PropertyTrees& operator=(const PropertyTrees& from);
 
+  // These maps map from layer id to the index for each of the respective
+  // property node types.
   std::unordered_map<int, int> transform_id_to_index_map;
   std::unordered_map<int, int> effect_id_to_index_map;
   std::unordered_map<int, int> clip_id_to_index_map;
   std::unordered_map<int, int> scroll_id_to_index_map;
   enum TreeType { TRANSFORM, EFFECT, CLIP, SCROLL };
 
+  // These maps allow mapping directly from a compositor element id to the
+  // respective property node. This will eventually allow simplifying logic in
+  // various places that today has to map from element id to layer id, and then
+  // from layer id to the respective property node. Completing that work is
+  // pending the launch of Slimming Paint v2 and reworking UI compositor logic
+  // to produce cc property trees and these maps.
+  std::unordered_map<ElementId, int, ElementIdHash>
+      element_id_to_effect_node_index;

[wkorman, 2017/01/09 21:41:55]

Checkpoint: have omitted the _map suffix that the four maps at line 530 - 534
use as it seems redundant, but wanted to call it out as it's deviant from
existing code. If this seems reasonable then I'd propose renaming the others as
well to remove it as subsequent patch. Else am happy to add _map.

[ajuma, 2017/01/10 00:02:36]

Seems reasonable, and renaming the rest to match in a subsequent patch sound
good.

+  std::unordered_map<ElementId, int, ElementIdHash>
+      element_id_to_transform_node_index;
+
   std::vector<int> always_use_active_tree_opacity_effect_ids;
   TransformTree transform_tree;
   EffectTree effect_tree;
   ClipTree clip_tree;
   ScrollTree scroll_tree;
   bool needs_rebuild;
   bool non_root_surfaces_enabled;
   // Change tracking done on property trees needs to be preserved across commits
   // (when they are not rebuild). We cache a global bool which stores whether
   // we did any change tracking so that we can skip copying the change status
@@ skipping 67 matching lines @@
   DrawTransforms& GetDrawTransforms(int transform_id, int effect_id) const;
   DrawTransformData& FetchDrawTransformsDataFromCache(int transform_id,
                                                       int effect_id) const;
 
   PropertyTreesCachedData cached_data_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_PROPERTY_TREE_H_