Swizzle shader output and blend when using GL_RED to implement kAlpha_8_GrPixelConfig

src/gpu/gl/builders/GrGLProgramBuilder.cpp

Index: src/gpu/gl/builders/GrGLProgramBuilder.cpp
diff --git a/src/gpu/gl/builders/GrGLProgramBuilder.cpp b/src/gpu/gl/builders/GrGLProgramBuilder.cpp
index 97fcce59b777313d690bc1d7d700529b67305e9f..1cf2cafa9ee423359e915794ec7dce1084c22822 100644
--- a/src/gpu/gl/builders/GrGLProgramBuilder.cpp
+++ b/src/gpu/gl/builders/GrGLProgramBuilder.cpp
@@ -10,6 +10,7 @@
 #include "GrAutoLocaleSetter.h"
 #include "GrCoordTransform.h"
 #include "GrGLProgramBuilder.h"
+#include "GrSwizzle.h"
 #include "GrTexture.h"
 #include "SkRTConf.h"
 #include "SkTraceEvent.h"
@@ -260,6 +261,20 @@ void GrGLProgramBuilder::emitAndInstallXferProc(const GrXferProcessor& xp,
     // asks for dst color, then the emit code needs to follow suit
     verify(xp);
     fFS.codeAppend("}");
+
+    // Swizzle the fragment shader outputs if necessary.
+    GrSwizzle swizzle;
+    swizzle.setFromKey(this->desc().header().fOutputSwizzle);
+    if (swizzle != GrSwizzle::RGBA()) {
+        fFS.codeAppendf("%s = %s.%s;", fFS.getPrimaryColorOutputName(),
+                        fFS.getPrimaryColorOutputName(),
+                        swizzle.c_str());
+        if (xp.hasSecondaryOutput()) {
+            fFS.codeAppendf("%s = %s.%s;", fFS.getSecondaryColorOutputName(),
+                            fFS.getSecondaryColorOutputName(),
+                            swizzle.c_str());
+        }
+    }
 }
 
 void GrGLProgramBuilder::verify(const GrPrimitiveProcessor& gp) {