Multiple detatched displays

Denville

Hello

My application uses several extra displays which are detatched from the desktop. All is well until I re-boot the system when XP insists on making these extra displays part of the desktop, thus stopping my application from working; I have to re-set the properties on each re-boot. That is the problem; here are some more details and subtlties:

The problem is evident in all combinations of cards I have tested and in two very different PC's. (I have tries nVidia, ATI and Colourgraphic single- and multi-channel display cards and in AGP/PCI and PCI/PCI combinations) so I think it is an OS issue and not specific to any particular manufacturer.

If I do not run my app, there is no problem (XP doesn't reset the desktop). Only after I have run my app does the problem occur. I have writen the smallest possible test app which simply enumerates the displays, gets a DC for each unattached display, then releases the DC and quits the app.

The desktop re-set actually takes place on log-on, not on re-boot. I get to the log-on screen ok, then when I log on (to any user), the secondary displays fire up and the desktop gets dispersed.

I have tried a couple of manufacturers' utilities which should force the required setup on start-up, and they probably do; but I guess this occurs before log-on.

A would be grateful for any suggestions, either to correct this behaviour, or to modify my app with an API call (I've not found one) that can detatch the secondary displays from the desktop as if I had changed the configuration manually in Display Settings (so there must be one!).

Many thanks for any help,
Denville.

Denville

Not to worry, I've fixed it. Thanks to anyone who was thinking about it for me.

Judas

...i would have totally jump on it if i had any clue of what the problem might have been.... but i have Zero experience with this... was hopeing someone knew....... How did you fix it?

Denville

Judas, thanks for the thought!

Well, here is an excerpt from an e-mail I just sent to my colleague in USA, which explains all (METCOM is my application that uses the secondary displays):

<The big remaining problem was that of the PC restoring the secondary displays to the desktop everytime I re-booted (it did this regardless of PC or video card combination). It only happend after I had run METCOM and I was fairly sure it was modifying the registry with the display parameters when I got the DC for the display (when it was a rogue desktop it had exactly these settings). I trawled the net and MSDN for a clue virtually all week then I came across an old W98 article on the MS site describing how to detach a display programatically. You use ChangeDisplaySettingsEx() which I had looked at about a dozen times and which has no reference to detaching a display; you do it by setting all the parameters in the structure to zero. By using this call on start-up I can re-claim any ill-behaved displays, but better, by using it on shut-down after relinquishing the DC it stops the problem from arising.>

Thanks again for the interest, nice to talk to you.

Sincerely,
Denville.