GrFP can express distance vector field req., program builder declares variable for it

src/gpu/glsl/GrGLSLFragmentShaderBuilder.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrGLSLFragmentShaderBuilder_DEFINED
 #define GrGLSLFragmentShaderBuilder_DEFINED
 
@@ skipping 78 matching lines @@
      * Subtracts sample coverage from the fragment. Any sample whose corresponding bit is not found
      * in the mask will not be written out to the framebuffer.
      *
      * @param mask      int that contains the sample mask. Bit N corresponds to the Nth sample.
      * @param invert    perform a bit-wise NOT on the provided mask before applying it?
      *
      * Requires GLSL support for sample variables.
      */
     virtual void maskSampleCoverage(const char* mask, bool invert = false) = 0;
 
+    /** Returns a variable name that represents a vector to the nearest edge of the shape, in source
+        space coordinates. */
+    virtual const char* distanceVectorName() const = 0;
+
     /**
      * Fragment procs with child procs should call these functions before/after calling emitCode
      * on a child proc.
      */
     virtual void onBeforeChildProcEmitCode() = 0;
     virtual void onAfterChildProcEmitCode() = 0;
 
     virtual const SkString& getMangleString() const = 0;
 };
 
@@ skipping 50 matching lines @@
        use the fragment position and/or sample locations. */
     static uint8_t KeyForSurfaceOrigin(GrSurfaceOrigin);
 
     GrGLSLFragmentShaderBuilder(GrGLSLProgramBuilder* program);
 
     // Shared GrGLSLFragmentBuilder interface.
     bool enableFeature(GLSLFeature) override;
     virtual SkString ensureFSCoords2D(const GrGLSLTransformedCoordsArray& coords,
                                       int index) override;
     const char* fragmentPosition() override;
+    const char* distanceVectorName() const override;
 
     // GrGLSLFPFragmentBuilder interface.
     void appendOffsetToSample(const char* sampleIdx, Coordinates) override;
     void maskSampleCoverage(const char* mask, bool invert = false) override;
     void overrideSampleCoverage(const char* mask) override;
     const SkString& getMangleString() const override { return fMangleString; }
     void onBeforeChildProcEmitCode() override;
     void onAfterChildProcEmitCode() override;
 
     // GrGLSLXPFragmentBuilder interface.
@@ skipping 49 matching lines @@
      * 1st child's 2nd child".
      */
     SkString fMangleString;
 
     bool       fSetupFragPosition;
     bool       fHasCustomColorOutput;
     int        fCustomColorOutputIndex;
     bool       fHasSecondaryOutput;
     uint8_t    fUsedSampleOffsetArrays;
     bool       fHasInitializedSampleMask;
+    SkString   fDistanceVectorOutput;
 
 #ifdef SK_DEBUG
     // some state to verify shaders and effects are consistent, this is reset between effects by
     // the program creator
     GrProcessor::RequiredFeatures fUsedProcessorFeatures;
     bool fHasReadDstColor;
 #endif
 
     friend class GrGLSLProgramBuilder;
     friend class GrGLProgramBuilder;
 };
 
 #endif