Added distance vector support for CircleGeometryProcessor

src/gpu/GrOvalRenderer.cpp

Index: src/gpu/GrOvalRenderer.cpp
diff --git a/src/gpu/GrOvalRenderer.cpp b/src/gpu/GrOvalRenderer.cpp
index aec9b76ba85f986236a0382fcb451f84beb5e2c2..d8fd3b8dbd54e381309e68b84b0bc399b1de9cad 100644
--- a/src/gpu/GrOvalRenderer.cpp
+++ b/src/gpu/GrOvalRenderer.cpp
@@ -83,10 +83,13 @@ public:
         fStroke = stroke;
     }
 
+    bool implementsDistanceVector() const override { return true; };
+
     const Attribute* inPosition() const { return fInPosition; }
     const Attribute* inColor() const { return fInColor; }
     const Attribute* inCircleEdge() const { return fInCircleEdge; }
     const SkMatrix& localMatrix() const { return fLocalMatrix; }
+
     virtual ~CircleGeometryProcessor() {}
 
     const char* name() const override { return "CircleEdge"; }
@@ -134,6 +137,11 @@ public:
                 fragBuilder->codeAppend("edgeAlpha *= innerAlpha;");
             }
 
+            if (args.fDistanceVectorName) {
+                fragBuilder->codeAppendf("%s = %s.z * (normalize(%s.xy) - %s.xy);",

[egdaniel, 2016/07/28 17:30:53]

I feel like this would read easier as something like devVec = normalize(in.xy) *
(in.z - d); where d is from above. Aka scale the vector by how far away we are.
I believe though both equations are the same.

[dvonbeck, 2016/07/28 17:55:14]

That wouldn't work because d is a number from 0-1, not from 0-radius. I could do
devVec = normalize(in.xy) * in.z * (1 - d). That looks easier to read, right?

[egdaniel, 2016/07/28 18:01:52]

Ahh yes duh.

Since we do in.z * (1-d) above, lets store that result in a variable earlier and
reuse it here.

[dvonbeck, 2016/07/29 15:08:55]

Done.

+                                         args.fDistanceVectorName, v.vsOut(), v.vsOut(), v.vsOut());

[egdaniel, 2016/07/28 17:30:53]

why not us fsIn() like the coverage code above?

[dvonbeck, 2016/07/29 15:08:55]

Done.

+            }
+
             fragBuilder->codeAppendf("%s = vec4(edgeAlpha);", args.fOutputCoverage);
         }