Remove the 0.5 bias from the ellipse edge function. This makes coverage drop to zero before we get …

src/gpu/GrOvalRenderer.cpp

Index: src/gpu/GrOvalRenderer.cpp
diff --git a/src/gpu/GrOvalRenderer.cpp b/src/gpu/GrOvalRenderer.cpp
index f233fcb22e4d7b1aa5203df75fada96a44ecc84f..293038958882f768ef3888e46151520e64777515 100644
--- a/src/gpu/GrOvalRenderer.cpp
+++ b/src/gpu/GrOvalRenderer.cpp
@@ -303,7 +303,7 @@ public:
             // avoid calling inversesqrt on zero.
             fragBuilder->codeAppend("grad_dot = max(grad_dot, 1.0e-4);");
             fragBuilder->codeAppend("float invlen = inversesqrt(grad_dot);");
-            fragBuilder->codeAppend("float edgeAlpha = clamp(0.5-test*invlen, 0.0, 1.0);");
+            fragBuilder->codeAppend("float edgeAlpha = clamp(-test*invlen, 0.0, 1.0);");
 
             // for inner curve
             if (ee.isStroked()) {