Objective

Fixes #273

#894 implemented the move-and-slide algorithm for building kinematic character controllers. However, our KCC examples don't actually use it yet! To demonstrate how it can be used, and have better KCC examples for Avian, we should update the examples.

Solution

Use MoveAndSlide for the kinematic_character_2d and kinematic_character_3d examples. This involved some tricky bits:

• Slope climbing and sliding is handled in the on_hit callback. This is the most complicated part. I partially adapted the logic from Rapier.
• The callback also tracks collisions. Contact forces are applied to dynamic bodies in a separate system.
• I really struggled to get characters not to slide down walkable slopes when standing still. This turned out to largely be a bug in cast_move; the skin width wasn't considered in the shape cast max_distance, causing the character to move past the skin width, at which point depenetration kicked in, moving the character along the normal, causing drift down the slope. This is now fixed.

I also improved the examples in general:

• Added TransformInterpolation
• Changed scheduling to collect inputs in PreUpdate and handle movement in FixedUpdate
• Added terminal velocity
• Made the component split a lot more sensible and got rid of bundles
• Made damping use exponential decay like LinearDamping does

Testing

Ran the examples a bunch of times.

Showcase

kinematic_character_3d

Previously, the box would fly away as soon as you stand on it or push it into a wall. With move-and-slide and manually applied impulses, this doesn't happen.