09_the_moon.frag

uniform vec2 u_resolution;

float stroke(float x, float s, float w){
	float d = step(s, x + w * .5) - step(s, x - w * .5);
	return clamp(d, 0., 1.);
}

float circleSDF(vec2 st){
	return length(st - .5) * 2.;
}

float fill(float x, float size){
	return 1. - step(size, x);
}

void main() {
	vec3 color = vec3(0.);
	vec2 st = gl_FragCoord.xy / u_resolution;
	
	color += fill(circleSDF(st), .65);
	vec2 offset = vec2(.1, .05);
	color -= fill(circleSDF(st - offset), .5);
	gl_FragColor = vec4(color, 1.);
}