Allow DDC brightness control through other applications

[DisplayPhil]

Dear DisplayLink team, thank you for implementing the feature of brightness control via DDC for MacOS, this is something that was missing in my setup for a long time so I had to use software dimming.

Now I would like to ask, if it would be possible to allow to control the monitor via DDC using a third party application. I use 4 monitors, two of which are connected via DisplayLink, and I use two popular open source programs in order to keep the brightness in sync between all of them. If DisplayLink could allow this program or any other to control the brightness of the monitors via DDC just like it is possible with the ones that that are natively connected, it would be amazing.

Thank you very much and I await your feedback.

[waydabber]

Hi all,

As the developer of MonitorControl and BetterDisplay (both are popular macOS apps to control displays), I'd be happy to add DDC support for DisplayLink. It would be great to have a simple API, maybe based on simple DistributedNotificationCenter notifications back and forth - this would probably be very simple to implement. If full DDC support is not feasible, simply allowing the currently exposed brightness and contrast controls would be great as well!

Best,
waydabber

ps. a user pointed me to this thread.

[Szymon]

Hello,

Thanks for the feedback and raising this request! It's an idea definitely worth considering. Currently, macOS doesn't support DDC/CI for virtual displays, therefore it requires to expose an API to connect with clients like BetterDisplay for brightness and contrast control.

I have passed your request to our engineering team for further discussion.

Regards,
Szymon

[samedwards]

It looks like the current implementation uses an XPC service for setting/getting the brightness, contrast, list of displays, and the ability to "flip" the display.

From what I can see, right now only the Manager application and Elgato's CameraHub application seem to be whitelisted to communicate with the XPC service, so I would imagine that there will need to be some method to get other applications authorized for this service

$ strings DisplayLink\ Manager.app//Contents/MacOS/DisplayLinkXpcService
[...]
DlmXpc::Service: Processing command to return list of displays
DlmXpc::Service: Processing command to %{public}@ display %{public}@
DlmXpc::Service: Processing command to set contrast to %{public}.2f for display %{public}@
DlmXpc::Service: Processing command to set brightness to %{public}.2f for display %{public}@
DlmXpc::Service: Processing command to set flip setting to %{public}@ for display %{public}@
DlmXpc::Service: Notifying clients that contrast of display %{public}@ was changed to %{public}.2f
DlmXpc::Service: Error associated with client: %{public}@
DlmXpc::Service: Notifying clients that brightness of display %{public}@ was changed to %{public}.2f
DlmXpc::Service: Notifying clients that flip setting of display %{public}@ was changed to %{public}@
DlmXpc::Service: Notifying clients that displays have changed. New displays list:
[...]
certificate leaf[subject.OU] = "73YQY62QM3"
certificate leaf[subject.OU] = "Y93VXCB8Q5"
identifier "com.displaylink.DisplayLink-Manager-XPC-Client" and (
identifier "com.displaylink.DisplayLink-Manager-XPC-Client-ObjC" and (
identifier "com.displaylink.DisplayLinkUserAgent" and 
identifier "com.elgato.CameraHub" and certificate leaf[subject.OU] = "Y93VXCB8Q5"
info[CFBundleShortVersionString] >= "1.12.1"
info[CFBundleShortVersionString] >= "1.11.0"
[...]

[DisplayPhil]

Thank you very much, Szymon. It would be amazing if the team can take a look and share their thoughts!

[waydabber]

Originally Posted by Szymon

I have passed your request to our engineering team for further discussion.

Regards,
Szymon

Thanks @Szymon - let me know if there is any update with this or my assistance is needed!