Add underlays and split off common overlay functionality

cc/output/overlay_strategy_underlay.h

Index: cc/output/overlay_strategy_underlay.h
diff --git a/cc/output/overlay_strategy_underlay.h b/cc/output/overlay_strategy_underlay.h
new file mode 100644
index 0000000000000000000000000000000000000000..8bc0860029499e7bef4aafc5ef4a37801fcd998a
--- /dev/null
+++ b/cc/output/overlay_strategy_underlay.h
@@ -0,0 +1,36 @@
+// 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.
+
+#ifndef CC_OUTPUT_OVERLAY_STRATEGY_UNDERLAY_H_
+#define CC_OUTPUT_OVERLAY_STRATEGY_UNDERLAY_H_
+
+#include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
+#include "cc/base/cc_export.h"
+#include "cc/output/overlay_candidate.h"
+#include "cc/output/overlay_processor.h"
+#include "cc/output/overlay_strategy_common.h"
+#include "cc/quads/render_pass.h"
+
+namespace cc {
+class StreamVideoDrawQuad;
+class TextureDrawQuad;
+
+// The underlay strategy looks for a video quad without regard to quads above
+// it. The video is "underlaid" through the same mechanism as the video hole -

[danakj, 2015/03/18 16:36:51]

The video hole mechanism was explicitly kept behind a VIDEO_HOLE flag and not
meant to ship in chrome itself. Why is this different?

[achaulk, 2015/03/18 16:51:34]

The plan AFAIK is to do as much of what the VIDEO_HOLE feature needed to do
inside here as we can instead, so platforms that need it can add this strategy
to their list and platforms that don't can ignore it

[alexst (slow to review), 2015/03/18 17:47:29]

I would prefer we strip out video hole references from here because they bring
out bad associations.

This is simply a way to fit a current scene to available hardware. In a more
general case, we have a stack of M quads and N available overlay layers to put
them into. We can split up those M quads in some fashion across N layers and
then composite those N layers in hardware. When one of the quads goes to a layer
below, we need a transparency in the layer above so the final result looks the
same. When the top most layer is the main framebuffer, we need to explicitly add
the black quad, but you can imagine a case with 3 layers stacked as
|framebuffer|video|controls| and controls would be placed into a new small
buffer which wouldn't require any black quads added, just its color cleared.

[achaulk, 2015/03/18 19:40:39]

Sure, I can remove the video hole mention

+// a black transparent quad blended normally.
+class CC_EXPORT OverlayStrategyUnderlay : public OverlayStrategyCommon {
+ public:
+  OverlayStrategyUnderlay(OverlayCandidateValidator* capability_checker,
+                          ResourceProvider* resource_provider);
+  bool Attempt(RenderPassList* render_passes_in_draw_order,
+               OverlayCandidateList* candidate_list) override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(OverlayStrategyUnderlay);
+};
+
+}  // namespace cc
+
+#endif  // CC_OUTPUT_OVERLAY_STRATEGY_UNDERLAY_H_