Calculate Zoomify TileGroups with Vips

TileGroups.cs

public static int MaxTileGroup(Layer layer)
{
    int x = layer.tiles_across-1;
    int y = layer.tiles_down-1;
    int n = 0;
    Layer below = layer.below;

    while(below != null)
    {
        n += below.tiles_across * below.tiles_down;
        below = below.below;
    }

    n += y * layer.tiles_across + x;


    return n / 256;
}

public static int MaxTileGroup(Layer layer)
{
    int x = layer.tiles_across-1;
    int y = layer.tiles_down-1;
    int n = 0;
    Layer below = layer.below;

    while(below != null)
    {
        n += below.tiles_across * below.tiles_down;
        below = below.below;
    }

    n += y * layer.tiles_across + x;


    return n / 256;
}

public static Layer BuildPyramid(Layer above, int width, int height)
{
    Layer layer = new Layer();
    layer.width = width;
    layer.height = height;

    layer.tiles_across = RoundUp(width, 256) / 256;
    layer.tiles_down = RoundUp(height, 256) / 256;

    if (above == null)
        layer.Sub = 1;
    else
        layer.Sub = above.Sub * 2;

    layer.below = null;
    layer.above = above;

    int limit = 256;

    if (width > limit || height > limit)
    {
        if ((layer.below = BuildPyramid(layer, (width + 1) / 2, (height + 1) / 2)) == null)
        {
            return null;
        }
        layer.N = layer.below.N + 1;
    }
    else
    {
        layer.N = 0;
    }

    return layer;
}

public static int RoundDown(int number, int multiple)
{
    return number - (number % multiple);
}

public static int RoundUp(int number, int multiple)
{
    return RoundDown(number + multiple - 1, multiple);
}

class Layer
{
    public int width { get; set; }
    public int height { get; set; }
    public int tiles_across { get; set; }
    public int tiles_down { get; set; }
    public int Sub { get; set; }
    public int N { get; set; }

    public Layer below { get; set; }
    public Layer above { get; set; }
}