Two faced FreeBSD - or is that two headed

Frank Jahnke jahnke at
Wed Oct 20 13:57:06 PDT 2004

There are a number of ways to run dual monitors on FreeBSD,  Leaving out
the option of having the same desktop on each monitor (which is not very
interesting), they are:

Independent X sessions on each monitor.  This gives you two totally
independent screens, each with its own desktop.  Advantages: you can run
hardware acceleration on each (OpenGL, DRI, etc.).  Disadvantages: you
cannot drag windows from one screen to the other.  I find this annoying.

Xinerama. This spreads a single desktop over the two monitors. 
Advantages: a single desktop is wonderful.  Disadvantages: no 3D
hardware acceleration at all; software 3D only on the primary monitor,
and none on the secondary (I think).  Also, not all applications are
Xinerama-aware, so you sometimes get dialog boxes split between the
monitors (half on one, half on the other).  Of course, you can simply
drag the box onto one monitor or the other.

MergedFB. Like Xinerama, except that it uses a single frame buffer for
both screens (Xinerama uses one for each monitor).  Advantages: Hardware
acceleration is available.  Disadvantages: some fiddling with the
graphics drivers to get the windows to behave like Xinerama (for window
placement and resizing).

If you have no need for hardware acceleration, I recommend you try
Xinerama to see how you like it.  It may well be good enough.  If you do
need acceleration, it is your call on which of the other two options
would be better.

I don't know your graphics card, so I have no advice to offer here.  It
is possible to use two different graphics cards (the one you have, and
the one integrated onto your motherboard) but I've not tried that.  I
use an old Matrox G450 in MergedFB mode (still on XFree 4.3.0; this
should work on as well).  It is no speed demon, but 2D quality is
nice, and speed is adequate for the few applications I have that require

In addition to googling on Xinerama, try
and for information on MergedFB.

I have XF86Config files for all of these modes (for the G450); unless
there is general interest I'd suggest you contact me off-list to get
them if they would help.

And good luck!

Frank Jahnke

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