Swizzle shader output and blend when using GL_RED to implement kAlpha_8_GrPixelConfig

src/gpu/gl/GrGLCaps.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #include "GrGLCaps.h"
 
@@ skipping 1530 matching lines @@
     }
 
     // If we don't have texture swizzle support then the shader generator must insert the
     // swizzle into shader code.
     if (!this->textureSwizzleSupport()) {
         for (int i = 0; i < kGrPixelConfigCnt; ++i) {
             glslCaps->fConfigTextureSwizzle[i] = fConfigTable[i].fSwizzle;
         }
     }
 
+    // Shader output swizzles will default to RGBA. When we've use GL_RED instead of GL_ALPHA to
+    // implement kAlpha_8_GrPixelConfig we need to swizzle the shader outputs so the alpha channel
+    // gets written to the single component.
+    if (this->textureRedSupport()) {
+        for (int i = 0; i < kGrPixelConfigCnt; ++i) {
+            GrPixelConfig config = static_cast<GrPixelConfig>(i);
+            if (GrPixelConfigIsAlphaOnly(config) &&
+                fConfigTable[i].fFormats.fBaseInternalFormat == GR_GL_RED) {
+                glslCaps->fConfigOutputSwizzle[i] = GrSwizzle::AAAA();
+            }
+        }
+    }
+
 #ifdef SK_DEBUG
     // Make sure we initialized everything.
     ConfigInfo defaultEntry;
     for (int i = 0; i < kGrPixelConfigCnt; ++i) {
         SkASSERT(defaultEntry.fFormats.fBaseInternalFormat !=
                  fConfigTable[i].fFormats.fBaseInternalFormat);
         SkASSERT(defaultEntry.fFormats.fSizedInternalFormat !=
                  fConfigTable[i].fFormats.fSizedInternalFormat);
         for (int j = 0; j < kExternalFormatUsageCnt; ++j) {
             SkASSERT(defaultEntry.fFormats.fExternalFormat[j] !=
                      fConfigTable[i].fFormats.fExternalFormat[j]);
         }
         SkASSERT(defaultEntry.fFormats.fExternalType != fConfigTable[i].fFormats.fExternalType);
     }
 #endif
 }
 
 void GrGLCaps::onApplyOptionsOverrides(const GrContextOptions& options) {}