Knob_atan2.hlsl

fixed4 frag(v2f IN) : SV_Target
{
    half2 uv = IN.texcoord.xy;

    fixed4 c = tex2D(_MainTex, uv) * IN.color;

    half a1 = atan2(uv.x - 0.5, 0.5 - uv.y);
    half a2 = atan2(ddx(uv.y), ddx(uv.x));

    c.rgb = max((a1 < a2) * c.r, c.g);
    
    return c;
}