Improve transitions in iOS 9 multitasking

[bwhtmn]

Leave GLview rendering on when app is inactive, to get nice smooth transitions between sizes when using multitasking on iPad (iOS 9).

[1ec5]

At the very least, the GL view needs to be inactive in the background on iOS 8.x and below, to avoid regressing #1050, #1186, #1203, #1243, and #1460. (It’s been quite a journey…) Can you verify that those crashes don’t occur in iOS 9?

[1ec5]

Ah, I misread the change: you’re only removing the case where the application becomes inactive, not the case where it goes entirely into the background. That’s probably considerably safer.

[bwhtmn]

Yup, this should apply to situations where the app is temporarily interrupted (e.g. multitasking or a system alert).

According to Apple's docs, you'd ideally want to throttle down the OpenGL frame rate when the app is inactive but I didn't see an easy way to do that.

[incanus]

you'd ideally want to throttle down the OpenGL frame rate when the app is inactive but I didn't see an easy way to do that.

Yeah, this is most commonly done in GLKView with a corresponding GLKViewController (preferredFramesPerSecond), which we don't use because we want to be a standalone view like MKMapView. Not seeing a shortcut way to do this.

[1ec5]

Thanks for this PR. An updated version is now being tracked as #2988.