After install Xorg from

/usr/ports/x11/xorg

as root edit /etc/X11/xorg.conf inserting at Section “Monitor”:

HorizSync 31-80<br /> VertRefresh 30-100<br /> ModelName "1600x900@60HZ"

In Section “Screen” add

DefaultDepth 24

and edit/add the resolution:

SubSection "Display"<br /> Viewport 0 0<br /> Depth 24<br /> Modes "1600x900"<br /> EndSubSection

where “Modes” is the screen proportion that you want.