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

src/gpu/glsl/GrGLSLFragmentShaderBuilder.h

Index: src/gpu/glsl/GrGLSLFragmentShaderBuilder.h
diff --git a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h
index 614b04f54b20a3467e4fb7e8d85afed3cb6ab623..9e6eec2004472d879b09cffaeb7ef16f2abe48d4 100644
--- a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h
+++ b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.h
@@ -53,6 +53,10 @@ public:
         is in device space (e.g. 0,0 is the top left and pixel centers are at half-integers). */
     virtual const char* fragmentPosition() = 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;

[egdaniel, 2016/07/14 02:47:47]

I think we can drop this down one level to grglslfpfragmentbuilder. The XP
should never need the distance vector. The gp probably doesn't need it either,
but we don't have anything that is FP only the GP builder inherits from the FP
one.

[dvonbeck, 2016/07/14 13:40:34]

Done.

+
     // TODO: remove this method.
     void declAppendf(const char* fmt, ...);
 
@@ -166,6 +170,7 @@ public:
     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;
@@ -235,6 +240,7 @@ private:
     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