jengine 0.3.0

Personal roguelike game engine.
Documentation 
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use image::{Rgba, RgbaImage};
use std::path::Path;

fn draw_bordered_rect(width: u32, height: u32, fill: [u8; 4], border: [u8; 4]) -> RgbaImage {
    let mut img = RgbaImage::new(width, height);
    for y in 0..height {
        for x in 0..width {
            let on_border = x == 0 || x == width - 1 || y == 0 || y == height - 1;
            img.put_pixel(x, y, Rgba(if on_border { border } else { fill }));
        }
    }
    img
}

fn draw_wall(width: u32, height: u32) -> RgbaImage {
    let mut img = RgbaImage::new(width, height);
    for y in 0..height {
        for x in 0..width {
            // Brick-row offset: every other row of bricks shifts by half-width.
            let brick_row = y / 6;
            let offset_x = if brick_row % 2 == 0 { 0 } else { width / 2 };
            let is_mortar_h = y % 6 == 0;
            let is_mortar_v = (x + offset_x) % (width / 2) == 0;
            let color = if is_mortar_h || is_mortar_v {
                Rgba([0x4A, 0x48, 0x45, 0xFF]) // dark mortar
            } else {
                Rgba([0x82, 0x74, 0x66, 0xFF]) // warm stone
            };
            img.put_pixel(x, y, color);
        }
    }
    img
}

fn draw_player(width: u32, height: u32) -> RgbaImage {
    let mut img = RgbaImage::new(width, height);
    // Yellow body
    let body = Rgba([0xF5, 0xD0, 0x30, 0xFF]);
    let dark = Rgba([0x80, 0x60, 0x00, 0xFF]);
    let eye = Rgba([0x10, 0x10, 0x10, 0xFF]);

    for y in 0..height {
        for x in 0..width {
            img.put_pixel(x, y, body);
        }
    }
    // Thin dark border
    for x in 0..width { img.put_pixel(x, 0, dark); img.put_pixel(x, height - 1, dark); }
    for y in 0..height { img.put_pixel(0, y, dark); img.put_pixel(width - 1, y, dark); }
    // Two pixel eyes at ~1/3 height
    let ey = height / 3;
    let ex1 = width / 4;
    let ex2 = 3 * width / 4;
    if ex1 < width && ey < height { img.put_pixel(ex1, ey, eye); }
    if ex2 < width && ey < height { img.put_pixel(ex2, ey, eye); }
    img
}

fn draw_small_enemy(width: u32, height: u32) -> RgbaImage {
    let fill = [0xCC, 0x22, 0x22, 0xFF];
    let border = [0x55, 0x00, 0x00, 0xFF];
    let mut img = draw_bordered_rect(width, height, fill, border);
    // Menacing eyes
    let ey = height / 3;
    let ex1 = width / 4;
    let ex2 = 3 * width / 4;
    let eye = Rgba([0xFF, 0xAA, 0x00, 0xFF]);
    if ex1 < width && ey < height { img.put_pixel(ex1, ey, eye); }
    if ex2 < width && ey < height { img.put_pixel(ex2, ey, eye); }
    img
}

fn draw_big_enemy(width: u32, height: u32) -> RgbaImage {
    let mut img = RgbaImage::new(width, height);
    let body = Rgba([0x66, 0x00, 0x88, 0xFF]);
    let border = Rgba([0xFF, 0x44, 0xFF, 0xFF]);
    let eye = Rgba([0xFF, 0xFF, 0x00, 0xFF]);

    for y in 0..height {
        for x in 0..width {
            let on_border = x == 0 || x == width - 1 || y == 0 || y == height - 1
                || x == 1 || x == width - 2 || y == 1 || y == height - 2;
            img.put_pixel(x, y, if on_border { border } else { body });
        }
    }
    // Large eyes
    let ey = height / 3;
    let ex1 = width / 4;
    let ex2 = 3 * width / 4;
    for dy in 0..3u32 {
        for dx in 0..3u32 {
            if ex1 + dx < width && ey + dy < height { img.put_pixel(ex1 + dx - 1, ey + dy - 1, eye); }
            if ex2 + dx < width && ey + dy < height { img.put_pixel(ex2 + dx - 1, ey + dy - 1, eye); }
        }
    }
    img
}

fn save_if_missing(path: &str, img: RgbaImage) {
    if !Path::new(path).exists() {
        img.save(path).unwrap_or_else(|e| eprintln!("build: could not save {path}: {e}"));
    }
}

fn main() {
    let dir = "resources/sprites";
    std::fs::create_dir_all(dir).expect("build: failed to create resources/sprites/");

    save_if_missing(&format!("{dir}/player.png"), draw_player(16, 24));
    save_if_missing(&format!("{dir}/small_enemy.png"), draw_small_enemy(16, 24));
    save_if_missing(&format!("{dir}/big_enemy.png"), draw_big_enemy(32, 48));
    save_if_missing(&format!("{dir}/wall.png"), draw_wall(16, 24));

    println!("cargo:rerun-if-changed=build.rs");
}