Kinematic Character Movement Slows Down on Steep Slopes

[hongha1412]

When using a kinematic character body in Rapier.js, the character slows down significantly when moving up steep slopes. The velocity decreases as the slope angle increases, while movement speed remains unchanged on flat surfaces and when moving downhill.

Expected Behavior:

• The character should maintain a consistent movement speed regardless of slope inclination.
• The slope should not introduce unintended deceleration when moving uphill.

Actual Behavior:

• The character's velocity decreases when moving up a slope.
• The steeper the slope, the slower the character moves.
• Movement downhill remains at a constant speed (same as on flat ground).

Steps to Reproduce:

• Create a KinematicCharacterController in Rapier.js.
• Set up a sloped surface (e.g., a static collider with an inclined angle).
• Move the character up and down the slope with a constant input velocity.
• Observe the slowdown effect when moving uphill.