[GEM Development] FreeGEM drivers updated
John Elliott
jce at seasip.demon.co.uk
Tue Mar 5 12:49:33 PST 2013
> Now that sounds rather peculiar, indeed; how do they/does the hardware cope
> if you have bits set in several planes? Presumably it's not actually a
> 16-colour mode in disguise; I guess the card assigns priorities to the
> planes or something?
A 1024x768x4 (or 768x1024x4) mode needs 192k of video RAM. The 4-colour
drivers map it as 4 x 48k planes:
- Red even columns
- Red odd columns
- Green even columns
- Green odd columns
So there are only two planes 'under' any given pixel. It also means, I
think, that half the bytes in any 4-plane MFDB will be unused.
--
John Elliott
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