Don't create render passes for transparent images.

cc/layer_tree_host_common.cc

 // Copyright 2011 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 "cc/layer_tree_host_common.h"
 
 #include "cc/layer.h"
 #include "cc/layer_impl.h"
 #include "cc/layer_iterator.h"
 #include "cc/layer_sorter.h"
@@ skipping 241 matching lines @@
     // If the layer flattens its subtree (i.e. the layer doesn't preserve-3d), but it is
     // treated as a 3D object by its parent (i.e. parent does preserve-3d).
     if (layerIsInExisting3DRenderingContext(layer) && !layer->preserves3D() && descendantDrawsContent)
         return true;
 
     // If the layer clips its descendants but it is not axis-aligned with respect to its parent.
     if (layerClipsSubtree(layer) && !axisAlignedWithRespectToParent && descendantDrawsContent)
         return true;
 
     // If the layer has opacity != 1 and does not have a preserves-3d transform style.
-    if (layer->opacity() != 1 && !layer->preserves3D() && descendantDrawsContent)
+    if (layer->opacity() != 1 && !layer->preserves3D() && layer->drawsContent() && descendantDrawsContent)
         return true;
 
     return false;
 }
 
 WebTransformationMatrix computeScrollCompensationForThisLayer(LayerImpl* scrollingLayer, const WebTransformationMatrix& parentMatrix)
 {
     // For every layer that has non-zero scrollDelta, we have to compute a transform that can undo the
     // scrollDelta translation. In particular, we want this matrix to premultiply a fixed-position layer's
     // parentMatrix, so we design this transform in three steps as follows. The steps described here apply
@@ skipping 204 matching lines @@
 
     // If we early-exit anywhere in this function, the drawableContentRect of this subtree should be considered empty.
     drawableContentRectOfSubtree = gfx::Rect();
 
     // The root layer cannot skip calcDrawTransforms.
     if (!isRootLayer(layer) && subtreeShouldBeSkipped(layer))
         return;
 
     gfx::Rect clipRectForSubtree;
     bool subtreeShouldBeClipped = false;
-    
+
     float drawOpacity = layer->opacity();
     bool drawOpacityIsAnimating = layer->opacityIsAnimating();
-    if (layer->parent() && layer->parent()->preserves3D()) {
+    if (layer->parent()) {
         drawOpacity *= layer->parent()->drawOpacity();
         drawOpacityIsAnimating |= layer->parent()->drawOpacityIsAnimating();
     }
 
     bool animatingTransformToTarget = layer->transformIsAnimating();
     bool animatingTransformToScreen = animatingTransformToTarget;
-    if (layer->parent()) {
+    if (layer->parent() && !layer->parent()->renderSurface()) {

[shawnsingh, 2012/11/26 19:03:08]

I think our discussion also applies to this if-statement, too, right?   i.e. the
XXXIsAnimating() accessors are computed properties that are reparented by a
surface, not properties given by the user of the compositor.

[danakj, 2012/11/26 19:09:44]

Yes, the check was added to the wrong if statement here. It would break the
screenSpaceTransformIsAnimating case here.

         animatingTransformToTarget |= layer->parent()->drawTransformIsAnimating();
         animatingTransformToScreen |= layer->parent()->screenSpaceTransformIsAnimating();
     }
 
     gfx::Size bounds = layer->bounds();
     gfx::PointF anchorPoint = layer->anchorPoint();
     gfx::PointF position = layer->position() - layer->scrollDelta();
 
     WebTransformationMatrix layerLocalTransform;
     // LT = Tr[origin] * Tr[origin2anchor]
@@ skipping 479 matching lines @@
 
         foundLayer = currentLayer;
         break;
     }
 
     // This can potentially return 0, which means the screenSpacePoint did not successfully hit test any layers, not even the root layer.
     return foundLayer;
 }
 
 }  // namespace cc