[ODE] newbie problem

[Cristian Bianchi]

Hi,
you must attach the bodies to the joint before setting its parameters (in
this case, BallAnchor), so just exchange "THIS LINE" with the previous one.
Cris

----- Original Message ----- 
From: "Ian McMeans" <imcmeans at telus.net>
To: <ode at q12.org>
Sent: Wednesday, March 31, 2004 9:35 AM
Subject: [ODE] newbie problem


> Hi, I'm trying to do a simple car simulation. Right now I'm not even
worried
> about collision detection, I'm just trying to get some joints interacting
> and drawn on the screen. I wrote some simple code to draw each dBody as a
> cube, and I know ODE is at least running (because I can watch my car
fall -
> there's no ground yet, so it falls forever).
>
> However, my problem is that if I attach the wheels (which are not at
origin)
> to the car (which happens to be at origin when the game starts) using a
> joint, then the position of the wheel changes to origin.
>
> Here is my code - I'm omitting the part where x,y, and z are computed, for
> brevity:
> Car::Car(dWorldID world) : wheelOffset(0.3, -0.1, 0.5)
> {
> dMass bodyMass, wheelMass;
> dMassSetBoxTotal(&bodyMass, 1000, 2 * wheelOffset.X(), 2 *
wheelOffset.Y(),
> 2 * wheelOffset.Z());
> dMassSetCylinderTotal(&wheelMass, 100, 1, 0.2, 0.1);
>
> body = dBodyCreate(world);
> dBodySetMass(body, &bodyMass);
> dBodySetPosition(body, 0, 0, 0); // car initially at origin
> shocksJointGroup = dJointGroupCreate(0);
>
> for (int wheel = 0; wheel < 4; wheel++)
> {
>     wheels[wheel] = dBodyCreate(world);
>     dBodySetMass(wheels[wheel], &wheelMass);
>
>     dBodySetPosition(wheels[wheel], x, y, z); // we have the wheel right
on
> the hinge2 anchor
>     shocks[wheel] = dJointCreateBall(world, 0);
>
>     dJointSetBallAnchor(shocks[wheel], x, y, z);
>     dJointAttach(shocks[wheel], body, wheels[wheel]);  // THIS LINE
> }
> }
>
> If I comment out the line I marked "THIS LINE", then the wheels are drawn
in
> the position I expect. What's going wrong? Are one of these functions
> expecting coordinates relative to (a) the joint, (b) the car, (c) the
wheel,
> and I'm supplying coordinates relative to something else?
>
> Thanks in advance!
> Ian.
>
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