uniform sampler2D texture;
uniform vec2 resolution;

vec4 circle(vec2 uv, vec2 pos, float rad, vec4 color) {
	float d = smoothstep(0.0, 2.0, length(pos - uv) - rad);
	float t = clamp(d, 0.0, 1.0);
	return vec4(color.rgb, color.a * (1.0 - t));
}

void main() {
    vec2 uv = gl_TexCoord[0].xy * resolution;
	vec2 center = resolution * 0.5;
	float radius = 0.49 * resolution.y;

    vec4 texture_color = texture2D(texture, gl_TexCoord[0].xy);
	vec4 layer1 = vec4(0.0, 0.0, 0.0, 0.0);
	vec4 layer2 = circle(uv, center, radius, texture_color);
	gl_FragColor = mix(layer1, layer2, layer2.a);
}