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

kernel vec4 scanline(sampler image, float opacity)
{
	vec2 coord = samplerCoord(image);
	vec4 pixel = sample(image, coord);
	
	float isOdd = mod(floor(coord.y), 2.0);

	// isOdd == 0 --> return pixel
	// isOdd == 1 --> return pixel * opacity
	
	//float multiplier = compare(isOdd - 1.0, 1.0, opacity);
	float multiplier = isOdd == 0.0 ? 1.0 : opacity;
	return pixel * multiplier;
}