keyboard input in X

[Rikard Björklind <olof@linux.nu>]

I'm writing a small game for X, using PTC to draw the graphics. The
problem is that I havn't been able to find out how to use the keyboard
for input; PTC's functions is like readkey. I need keyboard functions
that tell me whether a key is down or not.
How do I do this? I guess there are X library functions, but I don't
know where to start.
I would be very grateful if someone could give me a hint on this trivial
matter :)
Thanx,
/Rikard