gpu: Empty swaps for surfaceless output surfaces.

cc/output/direct_renderer.h

 // Copyright 2012 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_DIRECT_RENDERER_H_
 #define CC_OUTPUT_DIRECT_RENDERER_H_
 
 #include <memory>
 #include <unordered_map>
 #include <vector>
@@ skipping 169 matching lines @@
   const RendererSettings* const settings_;
   OutputSurface* const output_surface_;
   ResourceProvider* const resource_provider_;
   // This can be replaced by test implementations.
   std::unique_ptr<OverlayProcessor> overlay_processor_;
 
   // Whether it's valid to SwapBuffers with an empty rect. Trivially true when
   // using partial swap.
   bool allow_empty_swap_ = false;
   // Whether partial swap can be used.
   bool use_partial_swap_ = false;

[Daniele Castagna, 2017/04/19 19:10:36]

This names are a little bit confusing, or at least, it seems like a look at the
code is needed to clear out what they do.

Can we rename them?

Maybe explicitly mentioning if post_sub_buffers is used or not.

[reveman, 2017/04/19 23:59:03]

Sure. Either use_post_sub_buffer or use_sub_buffer_rect instead of
use_partial_swap might make this easier to read. I'll do that if other reviewers
agree.

+  // Whether non-empty partial swap should be allowed.
+  bool allow_partial_swap_ = false;
   // Whether overdraw feedback is enabled and can be used.
   bool overdraw_feedback_ = false;
   // Whether the SetDrawRectangle and EnableDCLayers commands are in
   // use.
   bool supports_dc_layers_ = false;
   // Whether the output surface is actually using DirectComposition.
   bool using_dc_layers_ = false;
   // This counts the number of draws since the last time
   // DirectComposition layers needed to be used.
   int frames_since_using_dc_layers_ = 0;
@@ skipping 47 matching lines @@
   gfx::ColorSpace reshape_device_color_space_;
   bool reshape_has_alpha_ = false;
   bool reshape_use_stencil_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(DirectRenderer);
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_DIRECT_RENDERER_H_