Rustで画素のバイト列をPPMフォーマットでファイルに書き出す

main.rs

use std::fs::OpenOptions;
use std::path::Path;
use std::io::BufWriter;
use std::io::Write;


// 画素
struct PIXEL {
    r: u8,
    g: u8,
    b: u8,
}

const WIDTH:  usize = 300;
const HEIGHT: usize = 300;
const SIZE:   usize = WIDTH * HEIGHT * 3;

fn main() {
    let mut ppm = [0u8; SIZE];
    create_image(&mut ppm);
    write_ppm("test.ppm", WIDTH, HEIGHT, &ppm);
}

// 市松模様
fn create_image(buf: &mut [u8; SIZE]) {
    for x in 0..WIDTH {
        for y in 0..HEIGHT {
            if ((x / 30 % 2) + (y / 30 % 2)) % 2 == 1 {
                let px = PIXEL{r: 255, g: 255, b: 255};
                set_pixel(px, x, y, WIDTH, HEIGHT, buf);
            } else {
                let px = PIXEL{r: 0, g: 0, b: 0};
                set_pixel(px, x, y, WIDTH, HEIGHT, buf);
            }
        }
    }
}

fn get_pixel(x: usize, y: usize, w: usize, h: usize, buf: &[u8; SIZE]) {
    let ind: usize = (y * h + x) * 3;
    PIXEL {r: buf[ind], g: buf[ind + 1], b: buf[ind + 2]};
}

fn set_pixel(px: PIXEL, x: usize, y: usize, w: usize, h: usize, buf: &mut [u8; SIZE]) {
    let ind: usize = (y * h + x ) * 3;
    buf[ind]     = px.r;
    buf[ind + 1] = px.g;
    buf[ind + 2] = px.b;
}

// PPM フォーマットでファイルに書き出し
fn write_ppm(filename: &str, width: usize, height: usize, bytes: &[u8]) {
    let path = Path::new(filename);
    let file = OpenOptions::new()
        .write(true)
        .create(true)
        .open(&path)
        .unwrap();

    let mut writer = BufWriter::new(&file);
    writer.write_all(b"P6\n").unwrap();
    writer.write_all(format!("{} {}\n", width, height).as_bytes()).unwrap();
    writer.write_all(b"255\n").unwrap();
    writer.write_all(bytes).unwrap();
}