Make GrGLShaderBuilder::fragmentPosition() return a vec4, with 1.0 as the zw components when in the…

src/gpu/gl/GrGLShaderBuilder.cpp

Index: src/gpu/gl/GrGLShaderBuilder.cpp
diff --git a/src/gpu/gl/GrGLShaderBuilder.cpp b/src/gpu/gl/GrGLShaderBuilder.cpp
index c2ebce2a912ae984ad5a7c54b74057c30715de1e..764d482389a122415d10f340b0404bd7e39d3947 100644
--- a/src/gpu/gl/GrGLShaderBuilder.cpp
+++ b/src/gpu/gl/GrGLShaderBuilder.cpp
@@ -499,7 +499,7 @@ const char* GrGLShaderBuilder::fragmentPosition() {
     // declaration varies in earlier GLSL specs. So it is simpler to omit it.
     if (fTopLeftFragPosRead) {
         fSetupFragPosition = true;
-        return "(gl_FragCoord.xy)";
+        return "gl_FragCoord";
     } else if (fGpu->glCaps().fragCoordConventionsSupport()) {
         if (!fSetupFragPosition) {
             SkAssertResult(this->enablePrivateFeature(kFragCoordConventions_GLSLPrivateFeature));
@@ -510,7 +510,7 @@ const char* GrGLShaderBuilder::fragmentPosition() {
                                       GrGLShaderVar::kUpperLeft_Origin);
             fSetupFragPosition = true;
         }
-        return "(gl_FragCoord.xy)";
+        return "gl_FragCoord";
     } else {
         static const char* kCoordName = "fragCoordYDown";
         if (!fSetupFragPosition) {
@@ -523,8 +523,11 @@ const char* GrGLShaderBuilder::fragmentPosition() {
             fOutput.fUniformHandles.fRTHeightUni =
                 this->addUniform(kFragment_Visibility, kFloat_GrSLType, "RTHeight", &rtHeightName);
 
-            this->fFSCode.prependf("\tvec2 %s = vec2(gl_FragCoord.x, %s - gl_FragCoord.y);\n",
-                                   kCoordName, rtHeightName);
+            // Using glFragCoord.zw for the last two components tickles an Adreno driver bug that
+            // causes programs to fail to link. Making this function return a vec2() didn't fix the
+            // problem but using 1.0 for the last two components does.
+            this->fFSCode.prependf("\tvec4 %s = vec4(gl_FragCoord.x, %s - gl_FragCoord.y, 1.0, "
+                                   "1.0);\n", kCoordName, rtHeightName);
             fSetupFragPosition = true;
         }
         SkASSERT(fOutput.fUniformHandles.fRTHeightUni.isValid());