On 4 Apr 96 at 5:58, Laszlo Vecsey wrote: [..]

...

In pseudo-C:

int retrace(void) { // test for video retrace #ifdef __MSDOS__ return (port[0x3da] & 8); // Some VGA, maybe EGA cards #else // your OS here #endif }

...

[..] x = 0; while (!retrace()) x++;

As far as I know, while(retrace()) will loop until vertical retrace begins, and then you call while(!retrace()) and that will loop until vertical retrace is over. (Or it may be the other way around).

Sloppy pseudo-C code. The code I've been experimenting with waits until it's no longer in a vertical retrace (if one is still active since the last sample) and then collects the sample when the next vertical retrace occurs. [..]

What if the screen is filled with different colors, or shapes. On some monitors you can actually see the size of the screen changing, warping out a little.. maybe the time for retrace will be different when painting screens with different data.

I haven't done a lot of tests yet.... and even then, it's probably very system specific. Rob. --- Send a blank message with the subject "send pgp-key" to <WlkngOwl@unix.asb.com> for a copy of my PGP key.