Comment 11 for bug 336721

One thing that may be exacerbating the problem is that for video drivers other than -nvidia, Xinerama no longer works, so bugs that are particular to Xinerama setups (even if not -nvidia specific) aren't getting much upstream attention. So I could imagine bit rot having laid in, bringing regressions with it.

For your test program, see if you can do it via a call to xwininfo using the -root and -display arguments (see man xwininfo).

If you'd like to write something yourself but the C coding is too intimidating, you can likely do it with X bindings in whatever language you're comfortable with. E.g. in python the python-xlib stuff should suffice. http://python-xlib.sourceforge.net/doc/html/python-xlib_4.html#SEC3