From: becka@rz.uni-duesseldorf.de
  To  : dok@fischlustig.de
  Date: Wed, 5 May 1999 18:07:41 +0200 (MET DST)

Re: Dynamic linking problem?

Hi !

> The ggi DGA target looks exactly the same like my working clanlib fbdev 
> target, which uses panning for flipping.
> An usleep(1) after the flip(pan) solves the flicker problem, 
> but the framerate is 45 instead of 148.

Yes - sure. You drop your framerate far enough below the refresh rate, which
makes the problem effectively disappear.

> Another strange thing is that the flickering comes in a rythmic way.
> (e.g. twice a second, then a second pause, twi...)

This is an artifact that is related to the frequency difference between the
refresh rate of the monitor and the frameswitch rate.

>     # D: 48.001 MHz, H: 46.876 kHz, V: 75.121 Hz

Look: 148Hz - 2*75Hz = -2Hz ... twice per second ...

This is like moving two transport belts at slightly different speeds and 
looking at the other while standing on one of them. If you have a marked 
point on them, this will seem to move at the difference in speed.
And if you only look at a certain point (e.g. at the start of the frame),
you cannot determine anymore, if the other belt moved two turns while you
did one, so you only see the difference to the closest multiple.

It's more or less a stroboscopic effect. You should be able to get any 
flicker rate you wish (up to f-refresh/2) by adjusting the frameswitch rate
carefully.

The problem is simply, that you need to synchronize with the screen refresh.

I'll see, if I can hack in support for that at least for KGIcon drivers.

What card do you have ? Maybe we can improve that one, too.

CU, ANdy

-- 
Andreas Beck              |  Email :  <Andreas.Beck@ggi-project.org>