highp vec4 circle(in highp vec2 uv, in highp vec2 pos, highp float rad, in highp vec3 color) {
    highp float d = length(pos - uv) - rad;
    highp float t = clamp(d, 0.0, 1.0);
    return vec4(color, t);
}
void fragment(){
	highp vec2 uv = FRAGCOORD.xy;
    highp vec2 res_xy = vec2(1.0/SCREEN_PIXEL_SIZE.x, 1.0/SCREEN_PIXEL_SIZE.y);
    highp vec2 center = res_xy*0.5;
    highp float radius = 0.05 * res_xy.y;

    highp vec4 layer1 = vec4(vec3(0.0), 0.0);
    
    highp vec4 layer2 = circle(uv, center, radius, vec3(0.0));

    COLOR = mix(layer1, layer2, layer2.a);
}