[ODE] Combing setpos'ed "ghost" bodies with a rigid central core? Doable?

[Colin Bonstead]

Yeah, this should be doable, that's how I do the "wall detector" around 
the avatar in our engine.  You shouldn't even need a rigid body, just a 
geom, since it won't be moved dynamically.  Just collide it and don't 
create any contact joints, just use the info for whatever you need.  
AFAIK there isn't any caching for geoms that will cause you any 
problems, at least I haven't run into any.

-----Original Message-----
 From: Megan Fox <shalinor at circustent.us>
Sent: Wed, 21 Jul 2004 12:54:38 -0600
To: Ode <ode at q12.org>
Subject: [ODE] Combing setpos'ed "ghost" bodies with a rigid central 
core? Doable?

Forgive the strange topic, let me explain:

I want both accurate collisions that match up with the skinned mesh
AND a physically active character.  If I start setpos'ing active
rigid bodies around, all hell is going to break loose - but would it
be practical for me to setpos bodies around IF those bodies were
considered "ghosts" by the rest of the world?  (eg. they exist only
as sensors to detect collision, never adding contact joints
themselves)

I would monitor the collision responses, and apply forces accordingly
- it wouldn't be 100% physically accurate, but enough to get sword
swings being interrupted if the player bashes a brick wall, knock
boxes around if they get bashed, register hits as valid if they
strike the player's arm (which would typically be a bit outside the
central cylinder body), etc.  A rigid box flying into an arm wouldn't
result in anything (aside from maybe assigning some damage to the
owner entity), but it would probably hit the central rigid body (and
assign force to the player that way) as explained below.

These "ghost" bodies would exist around a central rigid core, which
behaves just like anything else.  Hit it hard enough and send it
flying, movement is stopped by a heavy pile of stuff, ducking lowers
the height it "hovers" at, and so on - the standard "player as a
sphere/cylinder" representation.


My concern is that I'm not sure what sort of body position
persistence is going on behind the scenes - how exactly the
integrator is going to handle a body jumping from point A to B.  Will
it still break ODE to start setpos'ing things around, even if I avoid
the explosion problem by not adding any contact joints?

-Megan Fox / "Shalinor" Lead Developer, Elium Project
(http://www.elium.tk)

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