Need docs on DGA to track down possible bug

For about a year now, I've been using Xinerama mode to be able to use two
video cards and two monitors and still have a single desktop. But there
is still a bug (or maybe more than one) that keeps bothering me.

For example, I played two games (Quake2 and Vega Strike) and both of them
calculate mouse movements incorrectly which causes movement to the right
at incredible speed no matter where I move my mouse.

I am trying to track this problem down, but I'm not sure yet what is to
blame. I have made a small program which also exhibits some similar
problems, but I do not know enough about the functions/libraries to see
what is not working the way it should.

What I really need is some documentation on functions like
XF86DGADirectVideo. The only thing I found on the net is the manpage which
doesn't tell me enough.

If someone can point me to some more in-depth docs or is willing to answer
my questions on this issue, please let me know.

Thanks in advance,
Maurice.