where is the virtual screen code?

[Carlos Eduardo Rodrigues Diógenes]

Hi,

I search in the source code of x.org the code where is implemented the 
virtual screen, but I couldn't find it? Someone knows where it's 
implemented?

Maybe it's not very clear, but the code that I want to see is the one 
that manage the screen when you press <Ctrl><Alt><KP_+> and you can 
change the resolution and get an virtual screen.

Thanks,

Carlos.