Handle hot-plugging and graceful recovery of controllers

[Sean M. Pappalardo]

Mixxx should:
1) gracefully handle unplugging controllers mid-set
2) be able to see new controllers plugged in mid-set (when you go to the prefs)
3) automatically re-initialize a controller that went missing and is now visible again (Mixxx should start querying for controllers every half-second or so until the missing device re-appears (or the user opens the preferences window.) When the device reappears, Mixxx should automatically open and re-initialize it without any user interaction.)

I imagine 2 could be accomplished just by calling DeviceEnumerator::queryDevices() each time the prefs is opened.

[Sean M. Pappalardo (pegasus-renegadetech)]

The attached is a back trace of what happens when you unplug a controller mid-set. (In short, PortMIDI gets confused.)

[Be (be.ing)]

I could see this being confusing to new users. I could see a new user trying Mixxx for the first time, starting Mixxx, plugging in their controller, not seeing it in the preferences, and thinking that Mixxx does not support their controller even if it does.

[RJ Skerry-Ryan (rryan)]

Hotplug for HID is in progress here:
https://github.com/mixxxdj/mixxx/pull/191

[Be (be.ing)]

As a quick hack, maybe we could rescan for controllers when the preferences dialog is opened? Or add a "Refresh" button to the Controllers preference page?

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/5614