[Techtalk] Switching resolutions when I switch to an external monitor

[Mary]

On Thu, Mar 09, 2006, Akkana Peck wrote:
> You know about ctrl-alt-keypad_plus (and minus) for switching
> resolutions in the current X session, right?

Yes, but it seems like X has somehow 'forgotten' about the higher
resolution...

Here's a relevant snippet of my xorg.conf:

Section "Screen"
        Identifier      "Default Screen"
        Device          "Intel Corporation 82852/855GM Integrated
Graphics Device"
        Monitor         "Generic Monitor"
        DefaultDepth    24
[snips other depths]
        SubSection "Display"
                Depth           24
                Modes           "1024x768"
        EndSubSection
        SubSection "Display"
                Depth           24
                Modes           "1280x1024"
        EndSubSection
EndSection

Here's what xrandr has to say:
$ xrandr
 SZ:    Pixels          Physical       Refresh
*0   1024 x 768    ( 342mm x 271mm )  *60

I have a working "man xorg.conf" and here is what it has to say about
Modes:

    Modes  "mode-name" ...
    
    This  optional entry specifies the list of video modes to use.  Each
    mode-name specified must be in double quotes.  They must correspond
    to those specified or referenced in the appropriate Monitor section
    (including implicitly referenced built-in VESA standard modes).  The
    server will delete modes from this list which don’t satisfy various
    requirements.

Here's what my Monitor section looks like:

Section "Monitor"
        Identifier      "Generic Monitor"
        Option          "DPMS"
EndSection

I believe this means it is autoprobing the monitor. So my understanding
is that I can specify 1280x1024 (which is what parse-edid says my
external monitor is capable of!), but because the autoprobe doesn't find
it it won't work.

Now, the next thing I guess I could try would be to manually do a
"Monitor" section for the external monitor... but I don't know how to do
Monitor sections so that (a) it doesn't *assume* the external monitor is
there (it's a laptop, I carry it around!) and (b) I can switch to the
external Monitor definition *without* restarting X.

-Mary