Virtual Display ID changed at every reboot.

[JonnyF73]

Hello,

Is it possible to have the Device ID for the Virtual display remain persistent through reboots?

This is causing me an issue where I specify the Device ID in an app (Sunshine) for the Virtual display. Upon reboot the Device ID changes and my app will not startup correctly as it cannot find the virtual display which is now using another Device ID.

Thanks,

Jon.

[waydabber]

I am not sure what device ID the Sunshine app uses. The ID that should be used is the display's UUID (or maybe some of the natural identifiers) which is permanent for the app created virtual screens unless you change the natural identifiers. If it uses the CGDirectDisplayID, then it has a wrong implementation. Maybe you could confirm this with the app's dev.

[JonnyF73]

Hello, thanks, it uses the "Display ID" (sorry, I typed Device ID previously)

The Display ID changes upon every reboot... I would hope there is a way to make the Display ID persistent between reboots.

There is nothing the Sunshine Developer could do about this, as it is the Better Display app that does not retain the same Display ID.

Regards,

Jon.

[waydabber]

Hi there - the "Display ID" (CGDirectDisplayID) is not a permanent identifier, but a transient one. By coincidence for physical displays the identifier may be the same in subsequent reconnects if the number of displays and order of connecting them do not change - but it's just a coincidence and not guaranteed. No app should rely on this ID as a permanent ID, instead should use the display's UUID for that.

For more information on how to get the UUID: https://developer.apple.com/documentation/colorsync/cgdisplaycreateuuidfromdisplayid(_:)

For more information on the persistence of the DisplayID - please note the "typically remains constant until the machine is restarted":
https://developer.apple.com/documentation/coregraphics/cgdirectdisplayid

Please rely this info to the developer of the app, I am sure with this additional insight in mind he will be keen to fix the app.

[JonnyF73]

Thanks @waydabber, understood, thanks for the time for providing a detailed response... I assume my usage is a fringe case, hopefully they will update their system to accommodate, it's experimental though on macOS and windows Display ID tends to persist which is where the main development is, so I'm not holding out too much hope... fingers crossed eh!?

Cheers,

Jon.

[waydabber]

No problem. I am not sure about Windows, I think the underlying meaning of these identifiers are different/unrelated between the two platforms, overlaps in terminology are simply coincidences. It's really just one simple function call to get the UUID from the CGDirectDisplayID. Using the latter with the expectation that it will somehow be persistent or work properly is simply a coding bug so it should be fixed imho - the current approach won't work properly for normal displays either (but will present itself as a difficult to understand bug, as the identifier might feel somewhat persistent on certain configurations). The adverse effects will be more pronounced for any kind of virtual screen, not just BetterDisplay (examples: Sidecar, Vision Pro, Screen Sharing, AirPlay, DisplayLink displays etc).

But of course it's up to the developers of the app to decide what they do with this info. :)

[craigcabrey]

@JonnyF73 did you open an issue in the Sunshine repo?

[JonnyF73]

Can’t remember, I was told this is normal operation, and you shouldn’t use the virtual display if to reference the screen - but that’s what sunshine uses, so no solution as far as I know.Jon.Sent from my iPhoneOn 13 Jan 2025, at 09:42, Craig Cabrey ***@***.***> wrote: @JonnyF73 did you open an issue in the Sunshine repo? —Reply to this email directly, view it on GitHub, or unsubscribe.You are receiving this because you were mentioned.Message ID: ***@***.***>