Implement support for mixed sampled render targets

src/gpu/gl/GrGLGpu.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrGLGpu_DEFINED
 #define GrGLGpu_DEFINED
 
@@ skipping 430 matching lines @@
 
         void invalidate() {
             fSrcCoeff = kInvalid_GrBlendCoeff;
             fDstCoeff = kInvalid_GrBlendCoeff;
             fConstColorValid = false;
             fEnabled = kUnknown_TriState;
         }
     } fHWBlendState;
 
     TriState fMSAAEnabled;
+    TriState fCoverageModulationEnabled;

[Mark Kilgard, 2015/04/08 03:20:09]

is fCoverageModulationMode a better name for this?

technically NV_framebuffer_mixed_sample's isn't really an "enable" but rather a
mode.

While GL_RGBA is most typically used, GL_NONE (initial value), GL_ALPHA, and
GL_RGB are also supported.

I expect Skia's use of pre-multiplied alpha everywhere means GL_RGBA is the
interesting mode for Skia so if GL_NONE and GL_RGBA are the only options used,
that is kind of like an enable.

[vbuzinov, 2015/04/08 12:05:30]

Since we only use GL_RGBA at this point I thought it would be easier to reuse
skia's TriState enum for it.  So it is either modulation, no modulation or
unknown.  Changing this to unknown or some value wouldn't be hard, though.

Come to think of it, Brian earlier mentioned that "coverage modulation" might
sound ambiguous with regards to skia's own notion of coverage.  Should I rename
the var to fMixedSamplesCoverageModulationEnabled or do you guys think that
would be unnecessary -- coverage doesn't come up in GrGLGpu otherwise?

 
     GrStencilSettings           fHWStencilSettings;
     TriState                    fHWStencilTestEnabled;
 
 
     GrPipelineBuilder::DrawFace fHWDrawFace;
     TriState                    fHWWriteToColor;
     TriState                    fHWDitherEnabled;
     uint32_t                    fHWBoundRenderTargetUniqueID;
     SkTArray<uint32_t, true>    fHWBoundTextureUniqueIDs;
 
     ///@}
 
     // we record what stencil format worked last time to hopefully exit early
     // from our loop that tries stencil formats and calls check fb status.
     int fLastSuccessfulStencilFmtIdx;
 
     typedef GrGpu INHERITED;
     friend class GrGLPathRendering; // For accessing setTextureUnit.
 };
 
 #endif