Grayscale Visual Blocks

gistfile1.txt

float greyScale(in vec3 col) {
    return dot(col, vec3(0.2126, 0.7152, 0.0722)); 
}

void mainImage( out vec4 fragColor, in vec2 fragCoord ){
	vec2 q = fragCoord.xy / iResolution.xy;
    vec3 col = texture(iChannel0, q).rgb;
    vec3 res = vec3(greyScale(col));
	fragColor = vec4(res, 1.0); 
}