How to vary the pitch level depending on the camera altitude? Getting infinite loop and app crashes

[Robtles]

Hello,

I am trying to get a "Pokemon GO"-like effect, with the camera pitch varying depending on its altitude. I am restricting the camera zoom level from 17 to 19, so it's always close to the ground.

Aerial view:

Closer to the ground:

I have written a simple linear function that I plan to improve, returning a value (the pitch) that should always be between ~40 (for a zoom level of 17) and ~100 (for a zoom level of 19).

func pitchFor(_ altitude: Double = 420) -> CGFloat {
    return CGFloat(100 - ((altitude - 125) / 6.85))
}

Then I simply thought it would be enough to call mapViewRegionIsChanging delegate function, and updating the pitch from here:

func mapViewRegionIsChanging(_ mapView: MGLMapView) {
    let camera = MGLMapCamera(lookingAtCenter: mapView.camera.centerCoordinate, 
                                     altitude: mapView.camera.altitude, 
                                        pitch: pitchFor(mapView.camera.altitude), 
                                      heading: mapView.camera.heading)
    mapView.setCamera(camera, animated: true)
}

But I end up getting something that looks a lot like an infinite loop and then the app crashes:

Can you help me with that? I didn't know where to ask so I hope it's the right place, sorry if not.

Thanks for your help.

Configuration

Mapbox SDK versions: 4.9.0
iOS/macOS versions: 12.1.4
Device/simulator models: iPhone XR
Xcode version: 10.1

[1ec5]

Unfortunately, methods such as -mapViewRegionIsChanging: get called in response to programmatic camera changes in addition to user-initiated camera changes. So changing the camera within -mapViewRegionIsChanging: causes recursion unless you explicitly guard against it with a base case. For example, the method could bail if the pitch is already the same as what you’d change it to.

(Relatedly, #6908 tracks varying the maximum pitch by the altitude or zoom level.)

[Robtles]

Thank you for your answer, and all the work you're doing on this project.
Is there maybe another way to achieve this varying pitch feature, maybe from another delegate method? I have read the related issue and it looks like there is no easy way to do so, or maybe have I missed something.

[julianrex]

@StratRob until we fix the core underlying issue, I'd recommend trying to call setCamera from a DispatchQueue.main.async. See #14998 (comment) for a similar issue.

Can you please try this and let me know if this works for you? Thanks

[julianrex]

/cc @pozdnyakov for visibility

[stale]

This issue has been automatically detected as stale because it has not had recent activity and will be archived. Thank you for your contributions.

[nnhubbard]

Was this issue ever fixed @julianrex ?