Add default version of fsDistanceVector if it is required but not implemented

src/gpu/glsl/GrGLSLProgramBuilder.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "glsl/GrGLSLProgramBuilder.h"
 
 #include "GrPipeline.h"
@@ skipping 70 matching lines @@
 
 void GrGLSLProgramBuilder::emitAndInstallPrimProc(const GrPrimitiveProcessor& proc,
                                                   GrGLSLExpr4* outputColor,
                                                   GrGLSLExpr4* outputCoverage) {
     // Program builders have a bit of state we need to clear with each effect
     AutoStageAdvance adv(this);
     this->nameExpression(outputColor, "outputColor");
     this->nameExpression(outputCoverage, "outputCoverage");
 
     const char* distanceVectorName = nullptr;
-    if (this->fPipeline.usesDistanceVectorField() && proc.implementsDistanceVector()) {
+    if (this->fPipeline.usesDistanceVectorField()) {
         distanceVectorName = fFS.distanceVectorName();
         fFS.codeAppend( "// Normalized vector to the closest geometric edge (in device space)\n");
         fFS.codeAppend( "// Distance to the edge encoded in the z-component\n");
-        fFS.codeAppendf("vec4 %s;", distanceVectorName);
+
+        if (proc.implementsDistanceVector()) {
+            fFS.codeAppendf("vec4 %s;", distanceVectorName);
+        } else {
+            fFS.codeAppendf("vec4 %s = vec4(1,0,0,0); // not implemented by primitive processor\n",
+                            distanceVectorName);
+        }
     }
 
     // Enclose custom code in a block to avoid namespace conflicts
     SkString openBrace;
     openBrace.printf("{ // Stage %d, %s\n", fStageIndex, proc.name());
     fFS.codeAppend(openBrace.c_str());
     fVS.codeAppendf("// Primitive Processor %s\n", proc.name());
 
     SkASSERT(!fGeometryProcessor);
     fGeometryProcessor = proc.createGLSLInstance(*this->glslCaps());
@@ skipping 306 matching lines @@
         delete fFragmentProcessors[i];
     }
 }
 
 void GrGLSLProgramBuilder::finalizeShaders() {
     this->varyingHandler()->finalize();
     fVS.finalize(kVertex_GrShaderFlag);
     fFS.finalize(kFragment_GrShaderFlag);
 
 }