/*
 * simulate scanlines by darkening every other line.
 *
 */

kernel vec4 scanline(sampler image, float strength)
{

    vec4 fudge = vec4( 0.4, 0.4, 0.4, 0.0 );

    vec2 coord = samplerCoord(image);
	vec4 pixel = sample(image, coord);
	

    fudge *= strength;

    float yy = mod(coord.y, 2.0);

    fudge *= (yy < 1.0) ? 1.0 : -1.0;

    pixel = unpremultiply(pixel);
    pixel += fudge;
    return premultiply(pixel);

}