Write modes and logical graphics operations (eg. XOR)

[greg76]

@kitao I was trying to replicate some of the stuff I did as a teenager and I realised I can only specify a solid "fill color" for graphics operations like line, circle, etc. I'm not sure if even SDL exposes such functionality, but would be need to be able to generate differences of images, shapes.
There's a related thread about such SDL capabilities over stackoverflow:
https://stackoverflow.com/questions/39604288/how-to-xor-the-colors-under-a-shape-sdl2

I will try to check the performance if I implement this by using pget() & pset() but I'm afraid this will get pretty slow very quickly.

Back then, we used this on "chunky" VGA modes (8 bit 1 pixel), to emulate planar graphics modes where you would write to separate planes (8 bit per 8 pixel) and the multiple planes "laid on top of eachother" would define the color of a given pixel. eg.