I suggested in a previous blog entry that conferences should provide computers that speakers can use for their presentations. The reason for this is that getting one computer working with the beamer in each room is an easy task, while getting the laptop of every speaker to work is much more difficult.
It seems that my idea has been rejected by almost everyone who read it, so I'll document some tips for getting a laptop working.
SZ: Pixels Physical Refresh
*0 1400 x 1050 ( 474mm x 356mm ) *50
4 640 x 480 ( 474mm x 356mm ) 50
5 800 x 600 ( 474mm x 356mm ) 50
6 1024 x 768 ( 474mm x 356mm ) 50
8 1280 x 960 ( 474mm x 356mm ) 50
9 1280 x 1024 ( 474mm x 356mm ) 50
Firstly there is the command xrandr which can be used to change the resolution without logging out. Above are the most useful lines produced by running xrandr with no options on my Thinkpad T41p. The left column is the index to the list of resolutions. For example I run xrandr -s 9 to use mode 1280x1024 and xrandr -s 0 to use mode 1400x1050. This takes much less time than editing an X config file!
The next thing to note is that my Thinkpad has a refresh rate of 50Hz, apparently most beamers expect at least 60Hz, this explains why I have had ongoing problems in getting my Thinkpad to correctly work for presentations for the entire time that I have owned it. If you own such a Thinkpad then I recommend that you just bring another laptop to do your presentation on the assumption that the display possibly won't work and probably won't work properly! I had developed this habit anyway after repeated problems in getting my Thinkpad working (occurring on a number of occasions in several countries). It's good to now know the reason for this (thanks Keith).
When setting the resolution there are often tweaks that can be used. For example in my talk for the Debian Miniconf of LCA 2007 I used mode 800x600 (I think - Keith set it up and I didn't look closely after verifying that things basically worked). Even though the beamer didn't have good support for a low refresh rate it worked when the resolution was low enough. Fortunately the xrandr program allows changing resolution fast enough that all 13 resolutions could be attempted in about a minute.
The support for better display detection and configuration is steadily improving. Hopefully this year the problems will be solved (which means that for the Debian and RHEL releases in 2008 the problem will be solved).
A possible work-around is to use Xephyr (the replacement for Xnest). In a previous blog entry I described how to get Xephyr going for use by Xen images. It seems to be a common symptom of display synchronization problems that the edges of the screen will be clipped. The most common work-around for this is to not use the full-screen mode of OpenOffice - which means that instead of having a small amount of text clipped there is a large amount of OpenOffice menus etc on the screen. As Xephyr accepts any resolution it should not be difficult to arrange for it to use 98% of the screen space and then run the presentation full-screen in the Xephyr window. This will be particularly useful for programs such as MagicPoint (my favorite presentation program) which don't support a windowed mode of operation.
If you have any other suggestions on how to solve or work around display problems with laptops then please leave comments.