marc@cpsc.UCalgary.CA (Marc Schroeder) (02/05/90)
I posted here almost a week ago asking if anyone could tell me how
to flip between two graphics screens using the VBL interrupt.
Well, I didn't get any replies telling me how to do it, although
many people asked if they could have my results when I was done :-)
(BTW, almost all of my reply mail bounced back with a "host unknown",
or something similar.. If you want to re-write me, by all means ...)
I got it working on my own, and now have a slight degree of gray
scaling for diplaying certain specific pictures (I use it to display
the fractals I generate on a NeXT computer up at the university
on my monochrome monitor at home, which is originally why I wanted
to do the page flipping in the first place. Fratals are more
interesting in "colour").
The only problem is this: The flicker is annoying. It's not really
extreme unless you start working with more than 3 shades, but STILL.
The flicker would probably go away if I was doing the page flipping
on a colour monitor, between two colour images (to generate a
possibility of 512 colours on a medium rez. screen at a time instead
of 16), but that's just an educated guess (I havn't tried it).
I say this because if two corresponding bit mapped "pixels" are
roughly the same colour, as you flip between them there shouldn't
be a big shock to the eye. Rather, if you flip between a white
"pixel" and a black "pixel" at 70 Hz (I think that's the value,
or is it 60?), then they eye CAN perceive the change.
Can anyone think of a way to get rid of the flicker for a monochrome
picture? Maybe using the HBL would have certain advantages.
Thanks,
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Marc A. Schroeder * 1st year computer science
University of Calgary