cc : Simplify layer skipping logic

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 1226 matching lines @@
   if (parent_node)
     node->data.screen_space_opacity *= parent_node->data.screen_space_opacity;
 }
 
 void EffectTree::UpdateIsDrawn(EffectNode* node, EffectNode* parent_node) {
   // Nodes that have screen space opacity 0 are hidden. So they are not drawn.
   // Exceptions:
   // 1) Nodes that contribute to copy requests, whether hidden or not, must be
   //    drawn.
   // 2) Nodes that have a background filter.
-  // 3) Nodes with animating screen space opacity are drawn if their parent is
-  //    drawn irrespective of their opacity.
+  // 3) Nodes with animating screen space opacity on main thread or pending tree
+  //    are drawn if their parent is drawn irrespective of their opacity.
   if (node->data.has_copy_request)
     node->data.is_drawn = true;
-  else if (node->data.opacity == 0.f && !node->data.has_animated_opacity &&
+  else if (node->data.opacity == 0.f &&
+           (!node->data.has_animated_opacity || property_trees()->is_active) &&

[ajuma, 2016/04/12 21:48:14]

What if nothing triggers a property tree update on the active tree? (That is,
say we push property trees from the pending tree to the active tree, and there's
no animation to make needs_update true on the effect tree.)

[jaydasika, 2016/04/13 00:13:42]

Split this into 2 bools to handle the case.

[ajuma, 2016/04/13 14:33:15]

Hmm. Given that the effect tree is likely to only have a small number of nodes,
how about just setting needs_update to true on it when setting it on the pending
tree? (This keeps the code simpler and avoids growing nodes for things we can
easily recompute.)

[jaydasika, 2016/04/13 18:48:42]

Done.

            !node->data.has_background_filters)
     node->data.is_drawn = false;
   else if (parent_node)
     node->data.is_drawn = parent_node->data.is_drawn;
   else
     node->data.is_drawn = true;
 }
 
 void EffectTree::UpdateEffectChanged(EffectNode* node,
                                      EffectNode* parent_node) {
@@ skipping 692 matching lines @@
       break;
     case ALL_TREES:
       transform_tree.ResetChangeTracking();
       effect_tree.ResetChangeTracking();
   }
   changed = false;
   full_tree_damaged = false;
 }
 
 }  // namespace cc