uniform float percentagedistanceshow = 0.1;
uniform float gradientfalloffwidth = 0.2;

void fragment() {
    float dist = distance(UV, vec2(0.5, 0.5));
    float fromdiskdist = dist - percentagedistanceshow;
    COLOR.a = max(0, min(1.0, 2.0*dist/percentagedistanceshow - 2.0));
    COLOR.rgb = vec3(1,1,1) - vec3(fromdiskdist,fromdiskdist,fromdiskdist)/gradientfalloffwidth;
}