[ODE] Kinematic objects

Megan Fox shalinor at gmail.com
Sun Oct 30 20:28:59 MST 2005

The problem with this approach is that it depends on the
penalty-depenetration to keep things in shape, which is definately not
a safe bet.

Consider the case where a player is pushing a box into a wall... the
box wants to jump out of the way, but it can't push the player and
can't go through the wall.  This is an explosion waiting to happen.

You need to drive a player body with realistic forces, if you want
they to interact in a physical world that consists of more than static
geometry.  Kinematic bodies are only likely to work for special-case,
low-velocity things (like lifts) which you can absolutely prevent from
ever forcing a collision that could break the world.

(and I'd argue that even in those cases, a properly-modelled "true"
physical lift presents more gameplay possibilities - jumping on it
causing a bit of down force and jiggling, for instance, etc)

> I don't think using an ODE body is the way to go here.  To affect other
> "real" bodies, just create collisions with the world (against a null body).
> You don't need to simulate the accelaration of a kinematic body, just
> its instanteous velocity at each contact point.  These can then be
> translated into components for the contact joint parameters: motion1,
> motion2 and motionN.
> You may have to add support for motionN, it has been mentioned
> previously in the list, and its a fairly simple addition to the contact
> joint.
> I've simulated things like pendulums, swings, and lifts, and they work
> fine in collisions with real bodies.  Its ideal for situations where you
> having a moving object that interacts with the rest of ODE but is not
> affected itself.
> Geoff
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-Megan Fox
Lead Developer, Elium Project

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