Atari ST GEM-to-hardware palette mapping

witchspace · January 24, 2017

So I recently played around with GEM on Atari ST a bit, and palette setting, and (re-) discovered this weird mapping between GEM/VDI and hardware color mappings:

unsigned vdi_color_map[16] = { 0, 15, 1, 2, 4, 6, 3, 5, 7, 8, 9, 10, 12, 14, 4, 13 };

Asking GEM VDI to draw a line, v_line with vsl_color 15 would give you a line in... color 13!

I don't understand why they would do this. I really don't. Besides being confusing (it took me a while to figure out what was happening). It seems like a waste of resources, which was even more important on old, slow hardware. Why not just remap the palette?

There may be some really interesting reason I'm missing.

In any case I found this a curious old bit of computing history

Edit: sorry@moderator this probably belongs better here: https://atariage.com/forums/forum/175-atari-stttfalcon-programming/

Edited January 24, 2017 by witchspace