Backward slide frame interpolation flickers if steep enough (60fps)

[Richard-L]

I'm not 100% sure it's related to terrain angle, but it would suggest itself:

Typical:

https://github.com/LostArtefacts/TR1X/assets/4934209/e71f8182-2f82-49f7-a1c1-83b9caffca0e

Steep (a little hard to see the flicker):

https://github.com/LostArtefacts/TR1X/assets/4934209/9074a8f6-478a-46c2-84b6-cd80471b9c63

[Richard-L]

I also noticed that there can be slopes where Lara's model is moving fine and only her shadow is flickering:

https://github.com/LostArtefacts/TR1X/assets/4934209/95558f48-5b7a-401c-b24d-3843425da766