Keeping an object on a 2d plane ?

[greg2fs]

Hello, I am trying to kepp an object on a plane, witch seemed easy to me but I have problems to do that.
I use a matrix (rotation+translation) representing the position of the plane, this plane will move but for now I just put it on a fixed position an orientation.
I did something like that:
NewtonJoint* joint=NewtonConstraintCreateUserJoint(nWorld, 6, customcallback, objectbody, NULL);

Then in my callback I first calculate 3 points on my object with the same position in x ( A, B, C)
I next calculate the position of these points in the plane space, I modify their x position to 0 and recalculate their new position in the object space (I get newA, newB, newC)
To finish I add 3 linearrow , (one for each points) like that:
NewtonUserJointAddLinearRow (Joint, &A.x, &newA.x, &dir.x);

But my object stay on its "starting 2d plane" whatever position I take for my plane.

Is this method correct ?

THanks

[Gianluca]

No !!!
But your method is not far from the solution

Good idea to use a UserJoint ...
... but you need only a one LinearRow !!
In fact, the LinearRow constrain the position of your object along an axis ... and you need only to block movement along the normal of the plane

Lets A the position of your object ... then,
create newA as the project of A onto the plane
and then add the LinearRow:
NewtonUserJointAddLinearRow( Joint, &A.x, &newA.x, &plane_normal )
and newton will move the object along the normal of the plane until it reach the position newA that corrispond to a position on your plane.

That's it.

[greg2fs]

OK, but won't it be able to rotate on the 3 axis this way ?