DMXGetScreenCount (3) - Linux Manuals
DMXGetScreenCount: determine number of back-end screens
NAMEDMXGetScreenCount - determine number of back-end screens
Bool DMXGetScreenCount(Display *dpy, int *screen_count);
DESCRIPTIONDMXGetScreenCount() returns the number of back-end screens that a Xdmx(1) server controls. Since a DMX screen usually fills all of the available area on a back-end server, there is usually a one-to-one correspondence between DMX screens and backend servers. However, it is also possible for a DMX screen to cover only part of the available area on a back-end server, and for more than one DMX screens to occupy different parts of the visible area on the same back-end server.
A DMX screen may be managed as a regular X screen in the Xdmx(1) server or may be joined with other DMX screens using Xinerama.