Skip drawing unsupported layers in forced software mode

cc/trees/layer_tree_host_impl.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/trees/layer_tree_host_impl.h"
 
 #include <algorithm>
 
 #include "base/basictypes.h"
 #include "base/json/json_writer.h"
@@ skipping 621 matching lines @@
       if (occlusion_tracker.Occluded(
               it->render_target(),
               it->visible_content_rect(),
               it->draw_transform(),
               impl_draw_transform_is_unknown,
               it->is_clipped(),
               it->clip_rect(),
               &has_occlusion_from_outside_target_surface)) {
         append_quads_data.had_occlusion_from_outside_target_surface |=
             has_occlusion_from_outside_target_surface;
-      } else {
+      } else if (!output_surface_->ForcedDrawToSoftwareDevice() ||

[aelias_OOO_until_Jul13, 2013/05/29 22:30:47]

Seems like an arbitrary place to bail out... I suggest early-returning in
AppendQuadsForLayer() and AppendQuadsForRenderSurfaceLayer() based on the value
of append_quads_data.allow_tile_draw_quads .  (Alternatively we could exclude
this entire loop contents with a "continue" above occlusion_tracker.EnterLayer,
but I'm thinking the finer-grained early return would be easier to reason
about.)

[boliu, 2013/05/30 00:01:28]

Went with option 2 stead, skip the whole loop body if draw not supported. This
is because WillDraw/DidDraw call pairs might be doing somethings that are kind
of heavy (and possibly not supported?) in this mode. Eg, video layer acquires a
lock, texture layer creates resource, etc. Probably good to skip those as well.

+                 it->CanDrawInTilelessSoftwareMode()) {
         DCHECK_EQ(active_tree_, it->layer_tree_impl());
+
         it->WillDraw(resource_provider_.get());
         frame->will_draw_layers.push_back(*it);
 
         if (it->HasContributingDelegatedRenderPasses()) {
           RenderPass::Id contributing_render_pass_id =
               it->FirstContributingRenderPassId();
           while (frame->render_passes_by_id.find(contributing_render_pass_id) !=
                  frame->render_passes_by_id.end()) {
             RenderPass* render_pass =
                 frame->render_passes_by_id[contributing_render_pass_id];
@@ skipping 1588 matching lines @@
 }
 
 void LayerTreeHostImpl::SetDebugState(const LayerTreeDebugState& debug_state) {
   if (debug_state_.continuous_painting != debug_state.continuous_painting)
     paint_time_counter_->ClearHistory();
 
   debug_state_ = debug_state;
 }
 
 }  // namespace cc