Velocity integration of Kinematic bodies

Romain Daize
Posts: 15
Joined: Tue Jan 06, 2009 10:04 am

Velocity integration of Kinematic bodies

Post by Romain Daize »

Hi all,

Velocities (linear & angular) of kinematic bodies are not integrated into positions by Bullet world step itself. It seems it's done on purpose and we must integrate ourselves, but my question is why ? Finally we would like kinematic bodies to be integrated the same ways bodies are (so with the same algorithm), wouldn't we ? Moreover, how collision detection is done between kinematic and dynamic bodies ? For example setting body position each frame does not break continuous collision detection nor contact persistency ? Linear velocity is not used during one way collision detection between kinematic & dynamic bodies ? In my mind I would really like velocities of kinematic bodies integrated not by myself but by physic engine itself (as some integration equation can differ between my implementation and engine's one), some specific processes may be hidden to users so its own velocity integration implementation can be wrong with some internal physic engine methods.

Tell me if I'm wrong (may be this is just a bug...). Thanks for reply, and merry christmas ;)

Ro
Romain Daize
Posts: 15
Joined: Tue Jan 06, 2009 10:04 am

Re: Velocity integration of Kinematic bodies

Post by Romain Daize »

After some studies it seems that moving kinematic bodies can only be done by updating their positions, then finally linear & angular velocities are recomputed by Bullet itself at each simulation step. In my mind the contrary should be done, user should set velocities and bullet should update positions by integrating. Any opinion ?