/// Write a single palette index. Out-of-bounds coordinates are silently ignored.
#[allow(dead_code)]
pub fn set_pixel(dst: &mut [u8], dst_w: usize, x: i32, y: i32, color: u8) {
    let dst_h = (dst.len() / dst_w) as i32;
    if x < 0 || x >= dst_w as i32 || y < 0 || y >= dst_h {
        return;
    }
    dst[dst_w * y as usize + x as usize] = color;
}

/// Copy a rectangle out of `src` into a new Vec (for building sprites/glyphs).
#[allow(dead_code)]
pub fn extract(src: &[u8], src_w: usize, x: usize, y: usize, w: usize, h: usize) -> Vec<u8> {
    let mut out = vec![0u8; w * h];
    for row in 0..h {
        let s = src_w * (y + row) + x;
        let d = w * row;
        out[d..d + w].copy_from_slice(&src[s..s + w]);
    }
    out
}

/// Blit `src` (width `src_w`, height derived from src.len()) into `dst` at (dx, dy).
/// Clips against all four edges of `dst`; the destination position may be negative.
#[allow(dead_code)]
pub fn blit(dst: &mut [u8], dst_w: usize, dx: i32, dy: i32, src: &[u8], src_w: usize) {
    let dst_w_i = dst_w as i32;
    let dst_h = (dst.len() / dst_w) as i32;
    let src_h = (src.len() / src_w) as i32;

    for row in 0..src_h {
        let y = dy + row;
        if y < 0 || y >= dst_h {
            continue;
        }
        // Clip the horizontal span once per row, then copy it in one shot.
        let x0 = dx.max(0);
        let x1 = (dx + src_w as i32).min(dst_w_i);
        if x0 >= x1 {
            continue;
        }
        let d = dst_w * y as usize + x0 as usize;
        let s = (row * src_w as i32 + (x0 - dx)) as usize;
        let len = (x1 - x0) as usize;
        dst[d..d + len].copy_from_slice(&src[s..s + len]);
    }
}

/// Blit an 8×8 tile with transparency: index 0 is skipped.
/// Clips against all four edges of `dst`; the destination position may be negative.
pub fn blit_tile(dst: &mut [u8], dst_w: usize, dx: i32, dy: i32, tile: &[u8; 64]) {
    let dst_w_i = dst_w as i32;
    let dst_h = (dst.len() / dst_w) as i32;

    for row in 0..8i32 {
        let y = dy + row;
        if y < 0 || y >= dst_h {
            continue;
        }
        for col in 0..8i32 {
            let x = dx + col;
            if x < 0 || x >= dst_w_i {
                continue;
            }
            let px = tile[(row * 8 + col) as usize];
            if px != 0 {
                dst[dst_w * y as usize + x as usize] = px;
            }
        }
    }
}