Quote:
Originally Posted by Bruce Abbott
Basically unusable for anything except a demo running in DOS.
The way to do copper bars on VGA is to draw lines of different colors and change the palette entries to color cycle them. You have 256 colors so you can do 256 unique lines. If you want anything else on the screen you will have to give up some of those lines. This still requires CPU time to do the color cycling, but only needs to be done 'sometime' during blank or while racing the beam. Still a pain compared to a copper list, but possibly less CPU intensive than rendering each line in real time.
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In fact i've tried in past (not advanced try to be honest as i use DOS
DEBUG embedded assembler) just to quickly change RAMDAC zero color and it worked... somehow... Never had opportunity to try do something serious on this... Code was very simplistic - just sequence of 4 writes to particular I/O address - not much.
However using system timer with higher frequency was quite popular (like case for PC speaker when some interrupt rate was set even to 7..8kHz) line raster should be possible.