Key shader on whether frag pos read is relative to top-left or bottom-left

src/gpu/gl/GrGLProgramDesc.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrGLProgramDesc_DEFINED
 #define GrGLProgramDesc_DEFINED
 
@@ skipping 61 matching lines @@
         // Writes color*coverage as the primary color output and also writes coverage as the
         // secondary output. Only set if dual source blending is supported.
         kSecondaryCoverage_CoverageOutput,
         // Writes color*coverage as the primary color output and also writes coverage * (1 - colorA)
         // as the secondary output. Only set if dual source blending is supported.
         kSecondaryCoverageISA_CoverageOutput,
         // Writes color*coverage as the primary color output and also writes coverage *
         // (1 - colorRGB) as the secondary output. Only set if dual source blending is supported.
         kSecondaryCoverageISC_CoverageOutput,
         // Combines the coverage, dst, and color as coverage * color + (1 - coverage) * dst. This
-        // can only be set if fDstRead is set.
+        // can only be set if fDstReadKey is non-zero.
         kCombineWithDst_CoverageOutput,
 
         kCoverageOutputCnt
     };
 
     static bool CoverageOutputUsesSecondaryOutput(CoverageOutput co) {
         switch (co) {
             case kSecondaryCoverage_CoverageOutput: //  fallthru
             case kSecondaryCoverageISA_CoverageOutput:
             case kSecondaryCoverageISC_CoverageOutput:
                 return true;
             default:
                 return false;
         }
     }
 
     /** Non-zero if this stage has an effect */
     GrGLEffect::EffectKey       fEffectKeys[GrDrawState::kNumStages];
 
     // To enable experimental geometry shader code (not for use in
     // production)
 #if GR_GL_EXPERIMENTAL_GS
     bool                     fExperimentalGS;
 #endif
 
-    GrGLShaderBuilder::DstReadKey fDstRead;             // set by GrGLShaderBuilder if there
+    GrGLShaderBuilder::DstReadKey fDstReadKey;          // set by GrGLShaderBuilder if there
                                                         // are effects that must read the dst.
                                                         // Otherwise, 0.
+    GrGLShaderBuilder::FragPosKey fFragPosKey;          // set by GrGLShaderBuilder if there are
+                                                        // effects that read the fragment position.
+                                                        // Otherwise, 0.
 
     // should the FS discard if the coverage is zero (to avoid stencil manipulation)
     SkBool8                     fDiscardIfZeroCoverage;
 
     uint8_t                     fColorInput;            // casts to enum ColorInput
     uint8_t                     fCoverageInput;         // casts to enum ColorInput
     uint8_t                     fCoverageOutput;        // casts to enum CoverageOutput
 
     int8_t                      fFirstCoverageStage;
     SkBool8                     fEmitsPointSize;
     uint8_t                     fColorFilterXfermode;   // casts to enum SkXfermode::Mode
 
     int8_t                      fPositionAttributeIndex;
     int8_t                      fLocalCoordAttributeIndex;
     int8_t                      fColorAttributeIndex;
     int8_t                      fCoverageAttributeIndex;
 
     // GrGLProgram and GrGLShaderBuilder read the private fields to generate code. TODO: Move all
     // code generation to GrGLShaderBuilder (and maybe add getters rather than friending).
     friend class GrGLProgram;
     friend class GrGLShaderBuilder;
 };
 
 #endif