Shader Circle Drawing
When you draw a Circle, you need to measure dot's distance from origin of circle.
If distance from origin is longer than circle's radius, return 1(white),
if distance from origin is shoter than（when the radius is below 0.2） its radius, return 0 (brack).
fixed4 frag(v2f i) : SV_Target
{
fixed radius = 0.2;
fixed distanceFromOrigin = distance(i.uv, fixed2(0.2, 0.2));
return step(radius, distanceFromOrigin);
}
Reference
