Check for compositing when trying to use the presenter plugin
Instead of displaying a black screen with a pretty circle in it when there is no compositer, now we can display a black screen with a warning message!
It may seem better to disable the presentation plugin if compositing is not available, but the current KDE Connect protocol assumes the list of supported packet types is static and we can't check a plugin's working-ness before we send an identity packet. This last-minute error message at least has the benefit of telling the user what the problem is.
- Enable compositing
- Use phone to control presentation pointer -- A pretty halo should appear where the pointer is pointing
- Disable compositing (Alt + Shift + F12 by default on Plasma)
- Use phone to control presentation pointer -- A warning indicating you need to turn on compositing should appear