(see https://github.com/projectmesa/mesa/issues/1234).

We were trying to learn from the existing implementation in MASON, but we were not sure about how it is done in MASON.

Is it correct that the way it is done in MASON is by specifying a separate Field that is immutable, which contains the walls, which is rendered once for all? And then you have another Field where the agents dynamics takes place. If this is wrong, what is your recommendation for implementing such feature?

That's exactly how it's handled in MASON: but note that at present it only works with the "fast" field portrayals, that is, ones which draw objects as simple colored squares rather than letting the objects draw themselves.  If a field is immutable, MASON draws the field into a semitransparent buffered image (a picture), then splats the picture on the screen.  Thereafter if the drawn boundaries haven't changed, MASON just resplats the image.

Sean