Jitter during wall collisions with Bullet Physics: contact/penetration tolerance?
- by Niriel
I use the bullet physics engine through Panda3d.
My scene is still very simple, think 'Wolfenstein3d': tile-based, walls are solid cubes.
I expect walls to block the player, and I expect the player to slide along the walls in case of non-normal incidence.
What I get is what I expect, with one difference: there is some jitter. If I try to force myself into the wall, then I see the frames blinking quickly between two positions. These differ by about 0.04 units of distance, which corresponds to 4 cm in my game.
I noticed a 4 cm elsewhere: the bottom of my player capsule is 4 cm below ground, when at rest.
Does that mean that there is somewhere in the Bullet engine a default 0.04-units-long tolerance to differentiate contact from collision? If so, what should I do ? Should I change the scale of my game so that these 0.04 units correspond to 0.4 cm, making the jitter ten times smaller? Or can I ask bullet to change its tolerance to a smaller value?
Edit
This is the jitter I get: 6.155 - 6.118 = 0.036
LPoint3f(0, 6.11694, 0.835)
LPoint3f(0, 6.15499, 0.835)
LPoint3f(0, 6.11802, 0.835)
LPoint3f(0, 6.15545, 0.835)
LPoint3f(0, 6.11817, 0.835)
LPoint3f(0, 6.15726, 0.835)
LPoint3f(0, 6.11876, 0.835)
LPoint3f(0, 6.15911, 0.835)
LPoint3f(0, 6.11937, 0.835)
I found a setMargin method. I set it to 5 mm both on the BoxShape for the walls and on the Capsule shape for the player. It still jitters by about 35 mm as illustrated by this log (11.117 - 11.082 = 0.035):
LPoint3f(0, 11.0821, 0.905)
LPoint3f(0, 11.1169, 0.905)
LPoint3f(0, 11.082, 0.905)
LPoint3f(0, 11.117, 0.905)
LPoint3f(0, 11.082, 0.905)
LPoint3f(0, 11.117, 0.905)
LPoint3f(0, 11.0821, 0.905)
LPoint3f(0, 11.1175, 0.905)
LPoint3f(0, 11.0822, 0.905)
LPoint3f(0, 11.1178, 0.905)
LPoint3f(0, 11.0823, 0.905)
LPoint3f(0, 11.1183, 0.905)
The margin on the capsule did change my penetration with the floor though, I'm a bit higher (0.905 instead of 0.835). However, it did not change anything when colliding with the walls.
How can I make the collisions against the walls less jittery?
Edit, the day after:
After more investigation, it appears that dynamic objects behave well. My problem comes from the btKinematicCharacterController that I use for moving my character; that stuff is totally bugged, according to the whole Internet :/.
