[ltp] Getting nVidia to clone display on a projector

[John Jason Jordan]

On Mon, 22 Nov 2010 11:44:33 +0200
Micha Feigin <michf@post.tau.ac.il> dijo:

>It works for me with the nvidia driver using nvidia settings. You do
>need to make sure that you are working withing the projector specs.
>Most projectors these days can handle 1024x768
>
>I set the second screen to twinview mode and then set both screen to
>1024x768 duplicating each other and things never failed to work yet
>(apart for the problem of very partial support for embedded video
>playback in pdf presentation created using beamer).

Thanks for the reply. I have made some progress since my original post,
but I am not quite there yet. That is, I can get my laptop display to
appear on the wall with the projector, but I can't yet get an
acceptable resolution. The resolution is very important, as the
presentation I am going to give is on open source desktop publishing. I
need to squeeze pixels out of the projector until it screams.

First, to review, I have a T61 with nVidia Quadro NVS 140M, which
normally runs the 15.4" laptop screen at 1680x1050.

The projector in the classroom is a Hitachi CP-SX1350. Hitachi specs
say its native resolution is 1400x1050 and maximum resolution is
1600x1200. My (dim) understanding of the terms "native" and "maximum"
is that it can interpret data from a computer up to 1600x1200, but will
project no more than 1400x1050. Thus, if I were to set my computer
screen down to 1600x1000 (preserving the 16:10 widescreen aspect
ratio), the projector would accept this and then squash it down and
project 1400x875, with a black band on the top or the bottom for the
missing pixels (1050 - 875 = 175).

As an alternative, I could set my computer display down to 1400x875,
and then my laptop display and the projector display would be the same.
Either way, the maximum resolution I can project is 1400x1050.

The problem that remains, however, is getting my laptop screen to
display anything other than 1680x1050. I am currently using the latest
nVidia driver with Fedora 13, x86_64, and it allows me to select:

1680 x 1050
1280 x 1024
1280 x 960
1152 x 864 ... etc.

Once you install the nVidia driver, going back to the nouveau driver is
a pain. So I experimented instead by booting to a live CD of Ubuntu
Lucid. This uses the nouveau driver by default. The screen came up at
1680x1050, but the monitor settings utility allowed me to select from:

1680 x 1050
1400 x 1050
1280 x 1024
1280 x 960 ... etc.

While booted to Lucid I set the video to 1400x1050 and the screen
worked fine, although the aspect ratio was wrong. I did that just to
prove to myself that the screen itself can handle 1400x1050, even if
the nVidia driver doesn't think it can.

Installing the nVidia driver creates an xorg.conf file. Toward the
bottom of the file it lists modes as "nvidia-auto-select." I tried
commenting out that line, then adding my own modes, and restarting X.
The nVidia video settings utility still stubbornly refused to allow me
anything other than the list above. I also used cvt to create
modelines for other resolutions, then pasted them into the xorg.conf
file, but it still made no difference. I also tried setting the
resolution from the command line with xrandr, but the only resolutions
it would change to were the nVidia settings. If I tried (e.g.) "xrandr
-s 1400x1050," it would just give me an error that the resolution was
not possible.

It is odd that installing the nVidia driver created an xorg.conf file,
and then the driver ignores it.

I am trying to figure out where the nVidia driver is getting its list
of resolutions from. It's certainly not taking them from the xorg.conf
file. I assume that the nouveau driver got its list of resolutions by
querying the monitor for its EDID data. If so, then the nVidia driver
could not be getting its list of resolutions from EDID, else it would
also offer 1400x1050.

When I downloaded the driver from nvidia.com I noted that the same
driver works with quite a list of different cards. I am guessing that
nVidia hard coded the driver to list only resolutions that all those
cards were capable of. The driver is 260.19.21. If someone else is
using that driver with a different size screen than mine, it would be
interesting to see what resolutions the nvidia-settings utility offers.

Meantime, any other suggestions, corrections and observations are
welcome.