Optimizing the code part 2

optimizing_part2.rs

// -------- Our main function will change from this --------
fn main() {
    // {...}
    for y in (0..h as u64).rev() {
        for x in (0..w as u64).rev() {
            let mut color = Vec3::from(0.0);
            for _ in (0..samples_count).rev() {
                color = color
                    + trace(
                        position,
                        !(goal
                            + left * (x as f32 - w / 2.0 + random_val()).into()
                            + up * (y as f32 - 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);
        file.write_all(&[color.x as u8, color.y as u8, color.z as u8]).unwrap();
        }
    }
}

// -------- Into this ---------
fn main() {
    // {...}
    let mut pixels: Vec<(f32, f32)> = vec![];
    for y in (0..h as u64).rev() {
        for x in (0..w as u64).rev() {
            pixels.push((y as f32, x as f32));
        }
    }

    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();
}