Swizzle shader output and blend when using GL_RED to implement kAlpha_8_GrPixelConfig

src/gpu/glsl/GrGLSLCaps.h

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef GrGLSLCaps_DEFINED
 #define GrGLSLCaps_DEFINED
@@ skipping 90 matching lines @@
         return fSecondaryOutputExtensionString;
     }
 
     const char* externalTextureExtensionString() const {
         return fExternalTextureExtensionString;
     }
 
     /**
      * Given a texture's config, this determines what swizzle must be appended to accesses to the
      * texture in generated shader code. Swizzling may be implemented in texture parameters or a
-     * sampler rather than in the shader. In this case the shader swizzle will always be "rgba".
+     * sampler rather than in the shader. In this case the returned swizzle will always be "rgba".
      */
     const GrSwizzle& configTextureSwizzle(GrPixelConfig config) const {
         return fConfigTextureSwizzle[config];
     }
 
+    /** Swizzle that should occur on the fragment shader outputs for a given config. */
+    const GrSwizzle& configOutputSwizzle(GrPixelConfig config) const {
+        return fConfigOutputSwizzle[config];
+    }
+
     GrGLSLGeneration generation() const { return fGLSLGeneration; }
 
     /**
     * Returns a string containing the caps info.
     */
     SkString dump() const override;
 
 private:
     void onApplyOptionsOverrides(const GrContextOptions& options) override;
 
@@ skipping 16 matching lines @@
     const char* fFragCoordConventionsExtensionString;
     const char* fSecondaryOutputExtensionString;
     const char* fExternalTextureExtensionString;
 
     const char* fFBFetchColorName;
     const char* fFBFetchExtensionString;
 
     AdvBlendEqInteraction fAdvBlendEqInteraction;
 
     GrSwizzle fConfigTextureSwizzle[kGrPixelConfigCnt];
+    GrSwizzle fConfigOutputSwizzle[kGrPixelConfigCnt];
 
     friend class GrGLCaps;  // For initialization.
 
     typedef GrShaderCaps INHERITED;
 };
 
 #endif