slmvk@cc.usu.edu (04/22/91)
I have some questions on the dynamic hires/ham modes: 1. If I understand correctly, DHR uses a standard HiRes (640 width) screen, but changes the palette eveney line to give more colors. My question: why change the palette only once per line? I've seen demos that change palettes every eight pixels (hires copper resolution sucks!), so why can't DHR? Is it because it has to change all 16 colors? 2. How, exactly does DHA work? How come I never see anything that uses it? My guess: it changes the palette when necessary to eliminate the fringing effect of HAM. If this is true, wouldn't this be better in some ways than DHR? Also, what are the chances of C= ever introducing an upgraded copper chip (faster=higher horiz. resolution, I THINK)? Wy guess would be NEVER, because all previous programs that used copper lists would be totally messed! Jon Taylor SLMVK@cc.usu.edu
dvljrt@cs.umu.se (Joakim Rosqvist) (04/25/91)
In article <1991Apr22.101552.47507@cc.usu.edu> slmvk@cc.usu.edu writes: > > I have some questions on the dynamic hires/ham modes: > > 1. If I understand correctly, DHR uses a standard HiRes (640 width) >screen, but changes the palette eveney line to give more colors. My question: >why change the palette only once per line? I've seen demos that change >palettes every eight pixels (hires copper resolution sucks!), so why can't DHR? > Jon Taylor Colors can not be changed while the picture is being drawn because DHR uses 4-bitplane HIRES. That display mode requiers *every single* memory access. Since the display has priority over the copper the copper will have to wait until the HBLANK. Even there the timing is tough. In normal 640-mode the HBLANK interval is just enough for a wait and 16 colormoves but to be able to use DHR in overscan the 68000 will have to do some of the colors too. Sadly enough I think the 'DFF-bus' is 100% busy too, otherwise the 68000 could change some colors in the middle of a scanline when ran from fastram. In dynamic HAM though, the copper could change a palette value every 16 pixels so that mode could theoretically be improved. /$DR.HEX$