+
+ mediump vec2 v = abs(vPosition) - vRectSize;
+ mediump float cy = vCornerRadius + blurRadius;
+ mediump float cr = vCornerRadius + blurRadius;
+
+ cy = min(cy, min(vRectSize.x, vRectSize.y));
+ v = vec2(min(v.x, v.y), max(v.x, v.y));
+ v = v + cy;
+
+ mediump float blur = 1.0;
+ mediump float potential = 0.0;
+ mediump float alias = min(vCornerRadius, 1.0);
+ mediump float potentialMin = cy + vCornerRadius - blurRadius - alias;
+ mediump float potentialMax = cy + vCornerRadius + blurRadius + alias;
+
+ // move center of circles for reduce defact
+ mediump float cyDiff = min(cy, 0.2 * blurRadius);
+ cy -= cyDiff;
+ cr += cyDiff;
+
+ mediump float diffFromBaseline = cy * v.y - (cy + cr) * v.x;
+
+ if(diffFromBaseline > 0.0)
+ {
+ // out of calculation bound.
+ potential = v.y;
+
+ // for anti-alias when blurRaidus = 0.0
+ mediump float heuristicBaselineScale = max(1.0 , cr * (cr + cy));
+ mediump float potentialDiff = min(alias, diffFromBaseline / heuristicBaselineScale);
+ potentialMin += potentialDiff;
+ potentialMax -= potentialDiff;
+ }
+ else
+ {
+ // get some circle centered (x, x) and radius (r = cr / cy * x)
+ // s.t. point v is on that circle
+ // highest point of that circle is (x, x + r) and potential is x + r
+
+ // solve (v.x - x)^2 + (v.y - x)^2 = (cr / cy * x)^2
+
+ mediump float A = (cr * cr - 2.0 * cy * cy);
+ mediump float B = cy * (v.x + v.y);
+ mediump float V = dot(v,v);
+ mediump float D = B * B + A * V;
+ potential = V * (cr + cy) / (sqrt(D) + B);
+ }
+
+ blur = 1.0 - smoothstep(potentialMin, potentialMax, potential);
+ OUT_COLOR.a *= blur;
+}