cc: Compute target space transform dynamically

cc/layers/layer_impl.cc

Index: cc/layers/layer_impl.cc
diff --git a/cc/layers/layer_impl.cc b/cc/layers/layer_impl.cc
index 48a8f50176c617bef0e28cafe92f1681b2435647..57b4f6c495314903a526f05d705253a06de27f29 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -160,6 +160,15 @@ void LayerImpl::SetEffectTreeIndex(int index) {
   effect_tree_index_ = index;
 }
 
+int LayerImpl::render_target_effect_tree_index() const {
+  EffectNode* effect_node =
+      layer_tree_impl_->property_trees()->effect_tree.Node(effect_tree_index_);
+  if (effect_node->has_render_surface)
+    return effect_node->id;
+  else
+    return effect_node->target_id;
+}
+
 void LayerImpl::SetScrollTreeIndex(int index) {
   scroll_tree_index_ = index;
 }
@@ -1143,23 +1152,22 @@ gfx::Rect LayerImpl::GetScaledEnclosingRectInTargetSpace(float scale) const {
 
 RenderSurfaceImpl* LayerImpl::render_target() {
   EffectTree& effect_tree = layer_tree_impl_->property_trees()->effect_tree;
-  EffectNode* node = effect_tree.Node(effect_tree_index_);
-
-  if (node->render_surface)
-    return node->render_surface;
+  EffectNode* effect_node = effect_tree.Node(render_target_effect_tree_index());
+  if (effect_node->render_surface)
+    return effect_node->render_surface;
   else
-    return effect_tree.Node(node->target_id)->render_surface;
+    return effect_tree.Node(effect_node->target_id)->render_surface;
 }
 
 const RenderSurfaceImpl* LayerImpl::render_target() const {
   const EffectTree& effect_tree =
       layer_tree_impl_->property_trees()->effect_tree;
-  const EffectNode* node = effect_tree.Node(effect_tree_index_);
-
-  if (node->render_surface)
-    return node->render_surface;
+  const EffectNode* effect_node =
+      effect_tree.Node(render_target_effect_tree_index());
+  if (effect_node->render_surface)
+    return effect_node->render_surface;
   else
-    return effect_tree.Node(node->target_id)->render_surface;
+    return effect_tree.Node(effect_node->target_id)->render_surface;

[jaydasika, 2016/07/21 22:03:34]

Is this change required ? If target_effect_tree_index() checks render_surface
instead of has_render_surface like in the earlier patch, this won't be required,
right ?

[sunxd, 2016/07/22 14:41:17]

The render_target function is sometimes called before we ever create a render
target, in another word, at this time, effect_node->has_render_surface == true
but effect_node->render_surface == nullptr as we didn't create it.

[ajuma, 2016/07/22 15:05:48]

What's an example of such a callsite? One thing to worry about the way
render_target_effect_tree_index is currently defined is that for resourceless
software mode, non-root effect nodes might have has_render_surface = true even
though they can't have render surfaces (that is, will always have render_surface
== null), so defining render_target_effect_tree_index this way won't return the
effect_tree_index of the actual render target.

[sunxd, 2016/07/22 15:32:14]

I think that's when we cannot render to separate surfaces. Should I define it so
that it returns the root id in this case?

 }
 
 bool LayerImpl::IsHidden() const {