uniform vec3 color;
uniform float offset, sharpness;

void main()
{
	vec2 p = gl_TexCoord[0].st * 2.0 - 1.0;
	float d = max(length(p) - offset, 0.0);
	float vnt = pow(d, sharpness);

	gl_FragColor = vec4(color, gl_Color.a * vnt);
}