Switching between virtual desktops

[Luca Bezerra]

On Tue, Jun 2, 2009 at 10:58 AM, Matthijs Kooijman <matthijs at stdin.nl>wrote:

> Hi Luca,
>
> But that is on a single monitor. If I understand your intent correctly, you
> want to multiplex the signal over 10 different monitors, which is the real
> challenge here. I'm not so sure what a monitor does when you suddenly
> disconnect it for a (short) while, since it will probably lose the syncing
> signals.
>


> If you build your hardware clever enough so it will always connect
> the syncing signals to all monitors, and connect the signal pins to ground
> (or
> something) when the monitor is not "selected", this might work, provided
> that
> your monitor is "slow" enough (if it switches to black fast enough, you'll
> be
> looking at a monitor that is black 9/10th of the time).

   A: Well, the initial idea is to switch monitors so fast that maybe the
monitor wouldn't even "notice" that he got "disconnected", but I dont know
if thats possible either, since nowadays the monitors are having faster and
faster response times... Who would say the advances on technology could be
an obstacle to development, huh? :P

>
>
> Apart from that problem, I think timing will be critical here. Even if you
> can
> switch fast enough, you should make sure that you're switching the virtual
> desktop (ie, the image on the VGA output) at exactly the same moment as
> you're
> switching the output in your switchbox. Any offset here means that the
> image
> of one screen is visible on another screen, which might not bee all too
> noticable, but will probably lead to a lot of people with a headache in the
> long run.

A: The application running on the machine would deal with that. Its routine
would be something like this (obviously not this simple):

if (desktopChange())
{
    currentDesktop = getCurrentDesktop();
    currentMonitor = getCurrentMonitor();
    sendDataToParallelPort(currentDesktop,currentMonitor);
}

So it'd only switch the output after it has switched a virtual desktop,
making sure one wouldn't switch without the other.

>
> Not trying to demotivate you, but I have serious doubts about the
> feasibility
> of your approach (that, or I'm completely misunderstanding what you're
> trying
> to do...).
>
> Going down the typical multihead road with at least one VGA output per
> display
> is probably going to be a lot easier (but still challenging to get working
> properly probably, if you're going to share an X server between multiple
> users). I'd expect that PCI videocards should be available in plenty in the
> second hand market, lots of people still have them piling up at home I
> think.
> A: Dont worry, I know this isnt far from impossible, I also have doubts
> myself. The thing is, my boss has assigned me to this project, and so far,
> I've given him no concrete results, since every approach I've tried was a
> dead end.

As I've mentioned on an email to someone else (again, Im terrible with
names), Im pretty sure second hand hardware isnt really affordable for this
project, since we're inside a federal university, so every expense in here
has to be documented first, then approved by several departments before the
real money is released for the buying. I'm pretty sure there'll be no
approvals for 2nd hand pieces... Nevertheless, Im also in favor of using the
existing multiterminal (with multiple graphics boards) solution. Too bad its
not up to me to decide :P

Anyway, now I ask to all of you on this mailiing list. Supposing I just want
to make a script or something to automatically switch between desktops, not
involving multiple monitors, how would I do it, or where can I read more
about it? I havent finished reading about WMCtrl yet, but other than that,
does anyone have a suggestion?
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