#define pi 3.141592653589793238462643383279
#define twopi (pi * 2.0)
varying vec2 rcoords;

const float maxRad = 0.9;
const float minRad = 0.7;

void main() {
	float r = length(rcoords);
	vec4 color = gl_Color;
	if(r < minRad || r > maxRad)
		discard;

	float alpha = abs(r - (minRad + (maxRad - minRad) / 2.0));
	alpha /= (maxRad - minRad);
	alpha = 1.0 - alpha;
	color.a *= alpha;

	gl_FragColor = color;
}