Mac Overlays: Allow multiple overlays with sandwich strategy

cc/output/overlay_strategy_single_on_top.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 "cc/output/overlay_strategy_single_on_top.h"
 
 #include <limits>
 
 #include "cc/output/overlay_candidate_validator.h"
 #include "cc/quads/draw_quad.h"
 
 namespace cc {
 
 OverlayStrategySingleOnTop::~OverlayStrategySingleOnTop() {}
 
-bool OverlayStrategySingleOnTop::TryOverlay(
+QuadList::Iterator OverlayStrategySingleOnTop::TryOverlay(
     OverlayCandidateValidator* capability_checker,
     RenderPassList* render_passes_in_draw_order,
     OverlayCandidateList* candidate_list,
     const OverlayCandidate& candidate,
     QuadList::Iterator candidate_iterator,
     float device_scale_factor) {
   RenderPass* root_render_pass = render_passes_in_draw_order->back();
   QuadList& quad_list = root_render_pass->quad_list;
   const DrawQuad* draw_quad = *candidate_iterator;
   gfx::RectF rect = draw_quad->rect;
   draw_quad->shared_quad_state->quad_to_target_transform.TransformRect(&rect);
 
   // Check that no prior quads overlap it.
   for (auto overlap_iter = quad_list.cbegin();
        overlap_iter != candidate_iterator; ++overlap_iter) {
     gfx::RectF overlap_rect = overlap_iter->rect;
     overlap_iter->shared_quad_state->quad_to_target_transform.TransformRect(
         &overlap_rect);
     if (rect.Intersects(overlap_rect) &&
         !OverlayStrategyCommon::IsInvisibleQuad(*overlap_iter))
-      return false;
+      return quad_list.end();

[ccameron, 2015/09/02 22:22:33]

This shouldn't return the end() iter -- we want to keep trying!

   }
 
   // Add our primary surface.
   OverlayCandidateList candidates;
   OverlayCandidate main_image;
   main_image.display_rect = root_render_pass->output_rect;
   candidates.push_back(main_image);
 
   // Add the overlay.
   candidates.push_back(candidate);
   candidates.back().plane_z_order = 1;
 
   // Check for support.
   capability_checker->CheckOverlaySupport(&candidates);
 
   // If the candidate can be handled by an overlay, create a pass for it.
   if (candidates[1].overlay_handled) {
     quad_list.EraseAndInvalidateAllPointers(candidate_iterator);
+    DCHECK(candidate_list->empty());
     candidate_list->swap(candidates);

[ccameron, 2015/09/02 22:22:33]

here we want to return STOP -- this strategy only allows 1 overlay.

-    return true;
   }
-  return false;
+
+  return quad_list.end();

[ccameron, 2015/09/02 22:22:33]

likewise about keeping trying.

 }
 
 }  // namespace cc