I haven't optimized the base layer at all in my app, because I think it would double the surface count and increase the vertex count, eg each layer would need a non vertex alpha version, otherwise you'll get zbuffer problems.
If you want to speed things up, try doing it without those functions, calling them is doing alot more "For Next" loops than you really need too.
If you want to speed things up, try doing it without those functions, calling them is doing alot more "For Next" loops than you really need too.