Optimizing the code part 3

optimizing_with_rayon.rs

// -------- We change the relevant code in main() from this: --------
fn main() {
    // {...}
    let bytes: Vec<u8> = pixels.iter().flat_map(|(y, x)| {
            let mut color = Vec3::from(0.0);
            for _ in (0..samples_count).rev() {
                color = color + trace(position, !(goal + left * (*x - w / 2.0 + random_val()).into() + up * (*y - h / 2.0 + random_val()).into()));
            }
            color = color * (1.0 / samples_count as f32).into() + (14.0 / 241.0).into();

            let o: Vec3 = color + Vec3::from(1.0);
            color = Vec3::new_abc(color.x / o.x, color.y / o.y, color.z / o.z) * Vec3::from(255.0);
            vec![color.x as u8, color.y as u8, color.z as u8]
        }).collect();

    file.write_all(&bytes).unwrap();
}

// -------- Into this: --------
use rayon::prelude::*;
fn main() {
    // {...}                      
    let bytes: Vec<u8> = pixels.par_iter().flat_map(|(y, x)| {
                                // ^ notice this change
            let mut color = Vec3::from(0.0);
            for _ in (0..samples_count).rev() {
                color = color + trace(position, !(goal + left * (*x - w / 2.0 + random_val()).into() + up * (*y - h / 2.0 + random_val()).into()));
            }
            color = color * (1.0 / samples_count as f32).into() + (14.0 / 241.0).into();

            let o: Vec3 = color + Vec3::from(1.0);
            color = Vec3::new_abc(color.x / o.x, color.y / o.y, color.z / o.z) * Vec3::from(255.0);
            vec![color.x as u8, color.y as u8, color.z as u8]
        })
        .collect();

    file.write_all(&bytes).unwrap();
}