[Development] Why is libxcb needed if GUI is disabled in build?

[Mandeep Sandhu]

All,

I'm building the latest from dev branch using the following options
(on 64-bit Ubuntu 12.04):

-opensource -confirm-license -developer-build -release -no-gui
-no-widgets -no-cups -no-dbus -no-xcb

However the build fails with the following message:

The test for linking against libxcb and support libraries failed!
 You might need to install dependency packages, or pass -qt-xcb.

As I understand libxcb provided C language bindings for the X
protocol. However if GUI is disabled, why do we still need xcb? Is it
because X also handles mouse/keyboard input?

Also, it would be nice if the configure 'help' output would show which
options are selected by default, eg is "-gui" or "-no-gui" the default
option?

Thanks,
-mandeep