Determine if dmx is available
#include <X11/extensions/dmxext.h>
Bool DMXQueryExtension(Display *dpy, int *event_basep, int *error_basep);
DMXQueryExtension() determines if the DMX protocol extension is available. It will be available if the server is an Xdmx(1) server.
If the DMX protocol extension is available, event_basep and error_basep will be set to the event and error bases, respectively, and True will be returned. Otherwise, False will be returned.