Gimbal lock can be bypassed

[Amoki]

Is this bug fix critical for your commercial enterprise?
No

Describe the bug
The user can rotate the model upside down

To Reproduce
Steps to reproduce the behavior:
Load a model
Pivot to see the roof until you can't go further
Release the pivot
Start a new pivot and you can go beyond and make the model do frontflips.
Side effect: If you release the pivot with model upside down, the next pivot will force it to stand on the feet, making a 180° instantly.

Expected behavior
User can't rotate the model upside down

Screenshots

Screencast.from.2024-11-18.16-00-10.mp4

(I can manage to record my cursor, hope it's clear enough)

[paireks]

Hey @Amoki do you know if it's a regression or is it something that was always there?

[Amoki]

I just tried an old build, and it was already there 2 years ago

[paireks]

I tried to figure it out, and it looks like when you're looking exactly from the top it triggers different mode of rotation, which is this one:
https://github.com/xeokit/xeokit-sdk/blob/master/src/viewer/scene/CameraControl/lib/CameraUpdater.js#L126
and this specific rotation mode doesn't have a limitation of rotation, so you can do frontflips :)
I'm not sure how to limit this mode though to block frontflips. But at the same time I couldn't really find it problematic, that I can make these frontlips in this corner case (subjective opinion).
Historically it looks like this corner case exists, because rotation where we're looking exactly from the top makes the model disappear (if we try to treat it the same way as other roations). Related to: #289
This issue might be related to this one: #1020