wxGetKeyState() does not currently work on non-X11 GTK backends, and in some
cases it has been reported to crash. It seems that the most likely use case
for wxGetKeyState() is to query the modifier keys, so on non-X11 backends, use
GTK+ calls to retrieve the modifier key state.
Non-modifier keys are not currently implemented, update the documentation to
mention this.
Closes https://github.com/wxWidgets/wxWidgets/pull/322
(this is a combined backport of 1033fb048d,
9f9c09e24a and
a18fe083cc from master)
98065821bb