pub fn dilate(bitmap: &[u8], width: usize, height: usize, radius: u8) -> Vec<u8> {
    if radius == 0 || bitmap.is_empty() { return bitmap.to_vec(); }
    let r = radius as isize;
    let mut out = vec![0u8; width * height];
    for y in 0..height {
        for x in 0..width {
            let mut max_val = bitmap[y * width + x];
            for dy in -r..=r {
                for dx in -r..=r {
                    let ny = (y as isize + dy).clamp(0, height as isize - 1) as usize;
                    let nx = (x as isize + dx).clamp(0, width as isize - 1) as usize;
                    max_val = max_val.max(bitmap[ny * width + nx]);
                }
            }
            out[y * width + x] = max_val;
        }
    }
    out
}

pub fn thicken_light(bitmap: &[u8], width: usize, height: usize, strength: f32) -> Vec<u8> {
    if strength <= 0.0 || bitmap.is_empty() { return bitmap.to_vec(); }
    let mut out = bitmap.to_vec();
    let threshold = 64u8;
    let strength_byte = (strength * 255.0).clamp(0.0, 255.0) as u8;
    for y in 0..height {
        for x in 0..width {
            let idx = y * width + x;
            if bitmap[idx] >= threshold { continue; }
            let mut neighbor_max = 0u8;
            for dy in -1..=1isize {
                for dx in -1..=1isize {
                    if dy == 0 && dx == 0 { continue; }
                    let ny = (y as isize + dy).clamp(0, height as isize - 1) as usize;
                    let nx = (x as isize + dx).clamp(0, width as isize - 1) as usize;
                    neighbor_max = neighbor_max.max(bitmap[ny * width + nx]);
                }
            }
            if neighbor_max > threshold {
                out[idx] = out[idx].saturating_add(strength_byte);
            }
        }
    }
    out
}

pub fn r8_to_rgb(r8: &[u8]) -> Vec<u8> {
    let mut rgb = Vec::with_capacity(r8.len() * 3);
    for &v in r8 { rgb.push(v); rgb.push(v); rgb.push(v); }
    rgb
}

pub fn r8_to_rgba(r8: &[u8]) -> Vec<u8> {
    let mut rgba = Vec::with_capacity(r8.len() * 4);
    for &v in r8 { rgba.push(v); rgba.push(v); rgba.push(v); rgba.push(v); }
    rgba
}