The multi-monitor situation
===========================
Michael Stapelberg <michael+i3@stapelberg.de>
March 2010

…or: oh no, I have an nvidia graphics card!

== The quick fix

If you are using the nvidia binary graphics driver, you need to use the
+--force-xinerama+ flag when starting i3, like so (in your xsession):

.Example:
----------------------------------------------
exec i3 --force-xinerama -V >>~/.i3/i3log 2>&1 
----------------------------------------------

== The explanation

Starting with version 3.ε, i3 uses the RandR (Rotate and Resize) API instead
of Xinerama. This is due to the reason that RandR provides more information
about your outputs and connected screens than Xinerama does. To be specific,
the code which handled on-the-fly screen reconfiguration (meaning without
restarting the X server) was a very messy heuristic and most of the time did
not work correctly -- that is just not possible with the little information
Xinerama offers (just a list of screen resolutions, no identifiers for the
screens or any additional information). Xinerama simply was not designed
for dynamic configuration.

So, RandR came up as a more powerful alternative (RandR 1.2 to be specific).
It offers all of Xinerama’s possibilities and lots more. Using the RandR API
made our code much more robust and clean. Also, you can now reliably assign
workspaces to output names instead of some rather unreliable screen identifier
(position inside the list of screens, which could change, and so on…).

As RandR is around for about three years, it seemed like a very good idea to
us and it still is a very good one. What we did not expect, however, was the
nVidia binary driver. It still does not support RandR (as of March 2010), even
though nVidia announced that it will support RandR eventually. What does this
mean for you, if you are stuck with the binary driver for some reason (say
the free drivers don’t work with your card)? First of all, you are stuck with
TwinView and cannot use +xrandr+. While this ruins the user experience, the
more grave problem is that the nVidia driver not only does not support dynamic
configuration using RandR, it also does not even expose correct multi-monitor
information via the RandR API. So, in some setups, i3 will not find any
screens, in others it will find one large screen which actually contains both
of your physical screens (but it will not know that these are two screens).

For this very reason, we decided to implement the following workaround: As
long as the nVidia driver does not support RandR, an option called
+--force-xinerama+ is available in i3. This option gets the list of screens
*once* when starting and never updates it. As the nVidia driver cannot do
dynamic configuration anyways, this is not a big deal.

== See also

For more information on how to use multi-monitor setups, see the i3 User’s
Guide.