add reapply_lost_speed to KinematicCharacterController

[ntibi]

Adds reapply_lost_speed: bool to KinematicCharacterController

When set to true, the velocity lost by sliding will be reapplied to the corrected direction
so the character moves at the same speed wether it's sliding or not

[Vrixyz]

That condition should probably be in case there is no stairs ? otherwise we might end up intersecting with the stair. (and it might result in not going up the stair, or worse an infinite loop ?)

[ntibi]

indeed, but even with the reapply in the if !self.handle_stairs, reapplying the speed can be slightly flaky, especially in 3d

im turning the PR back into a draft and looking into it

[MeFisto94]

I guess kind of reworking the controller to not have the speed loss in the first place is not really possible? Would that result in loads of loop iterations of the slope sweeps?

I am asking because technically this behavior of slowing down/speeding up on slopes is not what one would expect from a character controller, especially contradicting the "kinematic" keyword. Same as the concept of "friction", it should usually always be infinite or zero.

For slopes specifically, the expectation (subjectively) is that one can climb them at full speed and descend them at full speed, unless the angle exceeds the maximum angle, then slipping is involved in some way.

My problem currently also is that I can't control which slopes to climb as the effect of the slope angles is too high, while also causing considerate CPU load (the loop that does the offset by the normal nudge and then raytraces again).

So, TLDR: This sounds like it solves problems of an actual dynamic character controller, not a kinematic one and properly getting that kinematic behavior may involve going back to the drawing board

Edit: Maybe it's a "simple" matter of gravity as well, because when I stopped applying gravity to the "input", I got a much better behavior at sliding (of course you can't drop down then), but obviously that fails on downward slopes. I'll try to see if I can do something about that just by conditionally having gravity on when not on ground or something.

Edit 2: The more I think about it it's related to manually applying gravity (I sure hope I copied that from some example), because the code in handle_slopes talks about the users intent based on the vertical component of input. For a character controller (and not say a plane), the verticle axis is most likely always 0 (or rather -9.81), probably invalidating all assumptions done in that method. But I am not too familiar with the code / logic involved to say for sure. All I know is that I stumbled over a youtube video that instead of nudging along the normal tried to handle slopes by following the surface tangent and correcting for the loss of remaining translation by re-normalizing to the previous magnitude.