cc::Fix computation of surface backfacing-ness when using property trees

cc/trees/layer_tree_host_common.cc

Index: cc/trees/layer_tree_host_common.cc
diff --git a/cc/trees/layer_tree_host_common.cc b/cc/trees/layer_tree_host_common.cc
index 4d14ff772a17136e83470fb4a32875d825aaf62a..377786c99e08e28ae22f7081dd70b048340161df 100644
--- a/cc/trees/layer_tree_host_common.cc
+++ b/cc/trees/layer_tree_host_common.cc
@@ -1760,13 +1760,16 @@ static void CalculateDrawPropertiesInternal(
     DCHECK(layer->render_surface());
     // Check back-face visibility before continuing with this surface and its
     // subtree
+    RenderSurfaceImpl* render_surface = layer->render_surface();
     if (!layer->double_sided() &&
         IsSurfaceBackFaceVisible(layer, combined_transform)) {
+      gfx::Transform draw_transform = combined_transform;

[ajuma, 2015/11/10 00:17:15]

Please add a comment that we need this logic since the surface-skipping code we
use later depends on the surface's draw transform.

+      draw_transform.Scale(1.0 / combined_transform_scales.x(),
+                           1.0 / combined_transform_scales.y());
+      render_surface->SetDrawTransform(draw_transform);

[jaydasika, 2015/11/09 22:56:45]

CDP and PT render surface draw transform don't match without this change.

[ajuma, 2015/11/09 23:31:21]

Is this because the "skipped" surface is still winding up in the RSLL, and
having its draw transform compared? See the suggestion below for possibly fixing
this.

       return;
     }
 
-    RenderSurfaceImpl* render_surface = layer->render_surface();
-
     if (IsRootLayer(layer)) {
       // The root layer's render surface size is predetermined and so the root
       // layer can't directly support non-identity transforms.  It should just
@@ -2478,12 +2481,6 @@ void CalculateRenderSurfaceLayerListInternal(
 
   if (render_to_separate_surface) {
     DCHECK(layer->render_surface());
-    if (!layer->double_sided() &&
-        IsSurfaceBackFaceVisible(layer, layer->draw_transform())) {
-      layer->ClearRenderSurfaceLayerList();
-      layer->draw_properties().render_target = nullptr;
-      return;
-    }
 
     if (use_property_trees) {
       RenderSurfaceDrawProperties draw_properties;
@@ -2504,6 +2501,14 @@ void CalculateRenderSurfaceLayerListInternal(
       layer->render_surface()->SetClipRect(draw_properties.clip_rect);
     }
 
+    if (!layer->double_sided() &&
+        IsSurfaceBackFaceVisible(layer,
+                                 layer->render_surface()->draw_transform())) {
+      layer->ClearRenderSurfaceLayerList();
+      layer->draw_properties().render_target = nullptr;

[ajuma, 2015/11/09 23:31:21]

Would calling RemoveSurfaceForEarlyExit here fix the CDP/PT draw transform
mismatch that you mention above (without the need for the code added earlier
that computes that draw transform of a skipped surface)?

[jaydasika, 2015/11/10 00:06:40]

No that won't still fix the mismatch. We either need to add the code in CDP(at
previous comment) or call draw_transform of layer for !use_property_tree case
here.

[ajuma, 2015/11/10 00:17:15]

Oh, I think I understand: the old code relied on the fact that when we
early-return in the code at the previous comment, the owning layer's transform
doesn't get reparented by the surface.

+      return;
+    }
+
     if (IsRootLayer(layer)) {
       // The root surface does not contribute to any other surface, it has no
       // target.