Mail Archives: djgpp/1997/02/12/06:08:34
On Tue, 11 Feb 1997, Christian Bird wrote:
> I've got a question that I think fits in this newsgroup. Right now I'm
> using allegro to do some programming with DJGPP. Whenever I use the 640
> by 480 by 256 colors mode the screen seems to shift to the right by an
> inch. In order for it to look right I have to use one of the dials on
> the monitor to shift it into the right place. Then when I revert back
> to the ole' dos prompt it's too far to the left so I have to switch
> back. I've never encountered this problem before. My question is: Has
> anyone else experienced this problem and if so how did they fix it. By
> chance might this have something to do with my graphics card or my
> monitor itself? Any help on the subject woul be greatly appreciated.
> thanks!
This has already been answered previously (something's wrong with my mail
feed!) but the complete answer is, for different resolutions, you have
different sync timings.
In general, to print a dot onscreen you need to sweep out the raster. Now
of the total dot clock available for drawing, you have to reserve some of
those dots for the borders of the screen (the electron gun in your monitor
goes blank during these intervals).
In your case, because the image shifted to the right, this means you have
to reduce the number of horizontal sync start pulses so that the image is
shifted to the left. Unfortunately, I know of no way to do this under DOS.
However, this problem is QUITE common under Linux when running X, so I've
gotten pretty adept at twiddling these values to get higher-than-VESA
refresh rates and resolutions (like 1152x900 on 1MB cards).
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