Mac Overlays: Allow multiple overlays with sandwich strategy

cc/output/overlay_strategy_common.h

 // Copyright 2015 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.
 
 #ifndef CC_OUTPUT_OVERLAY_STRATEGY_COMMON_H_
 #define CC_OUTPUT_OVERLAY_STRATEGY_COMMON_H_
 
 #include "cc/base/cc_export.h"
 #include "cc/output/overlay_candidate.h"
 #include "cc/output/overlay_processor.h"
 
 namespace cc {
 class IOSurfaceDrawQuad;
 class OverlayCandidate;
 class OverlayCandidateValidator;
 class StreamVideoDrawQuad;
 class TextureDrawQuad;
 
 class CC_EXPORT OverlayStrategyCommonDelegate {
  public:
   virtual ~OverlayStrategyCommonDelegate() {}

[ccameron, 2015/09/02 21:41:55]

It might be easier to read to create an enum for the return type, something to
the effect of STOP_TRYING_OVERLAYS or KEEP_TRYING_OVERLAYS. And then pass the
the "iter" argument by pointer (continuing on the theme from ListContainer).

[Andre, 2015/09/02 21:54:51]

Do you still want this change if ListContainer::Erase returns an Iterator just
like InsertBefore?
I slightly prefer returning an Iterator. I think passing iter by pointer is less
clear at the call site that it's an input+output argument, especially with that
big list of arguments.

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

I think there needs to be a clear "STOP_LOOKING_FOR_OVERLAYS versus
KEEP_LOOKING_FOR_OVERLAYS", and I think that the return value is the place for
it.

I think, actually, we need 3 return values
- CREATED_OVERLAY_STOP_LOOKING
  - in this case, we just return after TryOverlay
- CREATED_OVERLAY_KEEP_LOOKING
  - in this case, we keep calling TryOverlay. This requires that |iter| be
updated by TryOverlay (not too much to ask, because TryOverlay is already
already updated |candidate_list|
- DID_NOT_CREATE_OVERLAY
  - in this cause, we have to do ++iter

Blurgh, still not particularly clean.

[Andre, 2015/09/03 22:45:59]

Done.

-  virtual bool TryOverlay(OverlayCandidateValidator* capability_checker,
-                          RenderPassList* render_passes_in_draw_order,
-                          OverlayCandidateList* candidate_list,
-                          const OverlayCandidate& candidate,
-                          QuadList::Iterator iter,
-                          float device_scale_factor) = 0;
+  virtual QuadList::Iterator TryOverlay(
+      OverlayCandidateValidator* capability_checker,
+      RenderPassList* render_passes_in_draw_order,
+      OverlayCandidateList* candidate_list,
+      const OverlayCandidate& candidate,
+      QuadList::Iterator iter,
+      float device_scale_factor) = 0;
 };
 
 class CC_EXPORT OverlayStrategyCommon : public OverlayProcessor::Strategy {
  public:
   explicit OverlayStrategyCommon(OverlayCandidateValidator* capability_checker,
                                  OverlayStrategyCommonDelegate* delegate);
   ~OverlayStrategyCommon() override;
 
   bool Attempt(RenderPassList* render_passes_in_draw_order,
                OverlayCandidateList* candidate_list,
@@ skipping 20 matching lines @@
 
  private:
   OverlayCandidateValidator* capability_checker_;
   scoped_ptr<OverlayStrategyCommonDelegate> delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(OverlayStrategyCommon);
 };
 }  // namespace cc
 
 #endif  // CC_OUTPUT_OVERLAY_STRATEGY_COMMON_H_