This is a bit of a hack, maybe not an answer you’re looking for …
Sometimes I render ‘whole’ shapes in the Processing sketch, then apply the ‘boolean’ operation I desire in Inkscape (you might even automate this using Inkscape’s command line mode). So, the fill is one set of shapes, and the mask another. Additionally, you can separate shapes into layers to make the Inkscape work easier.
I’d rather expedite the process of getting results onto paper when I’m plotting, even if the sketch isn’t ‘fully-automated.’