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pub fn components_to_pixels(pixels: &mut Vec<u8>, r: &[i32], g: &[i32], b: &[i32], a: &[i32]) {
    for (r, (g, (b, a))) in r.iter().zip(g.iter().zip(b.iter().zip(a.iter()))) {
        pixels.extend_from_slice(&[*r as u8, *g as u8, *b as u8, *a as u8]);
    }
}

pub fn components_to_pixels_flat_map(r: &[i32], g: &[i32], b: &[i32], a: &[i32]) -> Vec<u8> {
    r.iter().zip(g.iter().zip(b.iter().zip(a.iter()))).flat_map(|(r, (g, (b, a)))| {
        [*r as u8, *g as u8, *b as u8, *a as u8]
    }).collect()
}

/*
pub fn generate_component(width: u32, height: u32) -> Vec<i32> {
    (0..width).zip(0..height).map(|(x, y)| {
        (x + y) as i32
    }).collect()
}

fn main() {
    use std::env;
    let width = env::args()
        .nth(1).unwrap_or_else(|| "4".to_string())
        .parse::<u32>()
        .expect("width must be an integer.");
    let height = env::args()
        .nth(1).unwrap_or_else(|| "4".to_string())
        .parse::<u32>()
        .expect("height must be an integer.");
    let r = generate_component(width, height);
    let g = generate_component(width, height);
    let b = generate_component(width, height);
    let a = generate_component(width, height);

/*
    let len = (width * height) as usize;
    let mut pixels = Vec::with_capacity(len * 4);
    components_to_pixels(&mut pixels, r.as_slice(), g.as_slice(), b.as_slice(), a.as_slice());
    */
    let pixels = components_to_pixels_flat_map(r.as_slice(), g.as_slice(), b.as_slice(), a.as_slice());
    println!("pixels = {:#?}", pixels);
}
// */