Have you tried the "grid" graphics package in R? It's the basis for ggplot. It's a bit of an unsung hero, the documentation is not great, but I think it is a very solid library.
Is it usable on its own? I only ever interacted with it in trying to hack around something I didn't like in ggplot, and it didn't seem like something I could use "by hand". In hindsight it does sound a lot like what MPL does. I can take a look!
