notification when the focused monitor switches?

[ST-Saint]

I want an explicit notification (e.g. notify-send) when the focused monitor changes. I tried to add an extra SHCMD associated with the focusmon function so it works when I manually switch the monitor, but it doesn't work when _NET_ACTIVE_WINDOW changes the monitor.

Is there any means to achieve that?

[bakkeby]

I checked and it looks like it is possible to achieve this by using the IPC patch and subscribing to monitor_focus_change_event.

$ dwm-msg subscribe monitor_focus_change_event
{"result":"success"}
{
    "monitor_focus_change_event": {
        "old_monitor_number": 0,
        "new_monitor_number": 1
    }
}

{
    "monitor_focus_change_event": {
        "old_monitor_number": 1,
        "new_monitor_number": 0
    }
}

{
    "monitor_focus_change_event": {
        "old_monitor_number": 0,
        "new_monitor_number": 1
    }
}

{
    "monitor_focus_change_event": {
        "old_monitor_number": 1,
        "new_monitor_number": 0
    }
}

It would be possible to have this drive the script that sends the notifications.