@kawa
Pretty unsolicited, but I've stumbled across you a few times in the past (starting years and years ago with the GBA Sappy program in maybe ~2007).
You like pixel art, right? Ever try MPS (Multi Paint System/Maguro Paint System) on the PC-98 or Sharp X68000? It's got problems but the way it implements dithering patterns with a mask is REALLY clever and explains why so many PC98 games used that specific dithering style.

Just something that might be fun for you to play with. IDK :P

If you know of anything that can do this that's more modern, I'm interested; I don't think Grafx2 does it.

P.S. - maybe I've said it before on your ACMLM forum, but I'm a fan!

(I also have contributed to that roguelike of yours a long time ago under a different name; added the linux build script.)