After setting the brightness on linux using "sudo ddcutil setvcp 0x10", is there a signal or callback function that can obtain the change in the brightness value

[wubw0508]

Recently, our project has implemented the use of ddcutil to set the brightness. However, if the brightness is set using the command "sudo ddcutil set VCP 0x10", no notification or callback function can be received

[rockowitz]

I believe what you're saying is that your application uses libddcutil, and you would like it to notify your client program if brightness is changed by command line ddcutil. This is architecturally not possible. Each instance of command line ddcutil and libddcutil is independent and there is no communication among them. For this to change, libddcutil would have to be running as a service. Michael Hamilton's ddcutil-service does do this. Second, command line ddcutil would have to use this service. However, this service exposes only a small subset of libddcutil functionality (though probably enough for your purposes). Moreover, ddcutil does not, as one might assume, use libddcutil. There is a lot of functionality in the former that is unimplemented in the latter.

If all you're interested in is brightness, your application could periodically poll feature x10. If you want to watch for a change to any feature, your can periodically read feature x02 (new control value), then read feature x52 to get the id of the feature that has changed, and then read that feature value. Unfortunately, in my experience, using features x02/x52 is unreliable.