Replaced main operation queue with user initiated queue

[fajdof]

Hi @scihant , Performing motionManager.startDeviceMotionUpdates on main queue caused very strong lagging on iPhone X. I updated it so it uses a user initiated queue which I think is suitable for this case. From Apple's documentation: "Used for performing work that has been explicitly requested by the user, and for which results must be immediately presented in order to allow for further user interaction."

[scihant]

Hi,

I've just tested the code on an iPhoneX before and after your changes, and haven't noticed any difference. In both cases it seems to work properly. Are you sure that the library is the cause of the delay and you're not doing something in background that lowers the performance?

[fajdof]

Hi, I just have a view controller with CTPanoramaView and a loaded image. When I move the iPhone X (iOS 11.2.5) the image moves some 1-3 seconds later. Tested on iPhone 6 and 6s and it seems to be working fine there. When I replace the main queue with user-initiated, everything works smoothly (didn't change anything else).

Also noticed that when running with main queue if I increase the deviceMotionUpdateInterval, the lagging becomes shorter. But switching to different queue completely removes lagging.

[scihant]

Ok, it wouldn't hurt anyway.

In your code, whenever the control method is changed, a new queue is created. I think it would be better if you make that queue a lazy member just like cameraNode is and then use it directly when starting motion updates.

    private lazy var opQueue: OperationQueue = {
        return ...
    }()

If you make that change and amend your commit (so that the result is a single commit again), I'll merge it.

Thanks.

[fajdof]

Hi, Sure, it's better if it's lazy. Updated the pull request with amended commit.

[scihant]

Thank you for your contribution.