Set pin of CreateCustomJoint

[samisaham]

I am trying to get a hinge joint to function, but am having trouble understanding how the pin of a custom hinge is represented in a matrix.
I think my issue is that I don't understand how Matrix's work well. Would someone please explain how matrix's work or point me to a source that I can learn from, and help me to set the pin of this joint?

Thank you!

Code: Select all

//Using Newton 2.09 beta
dMatrix matrix;
matrix = GetIdentityMatrix();
matrix.m_posit.m_x = xOrig;
matrix.m_posit.m_y = yOrig;
matrix.m_posit.m_z = zOrig;

//This is my trouble.  I have the pin I want, represented by a vector(xPin,yPin,zPin) and I want to apply it to the joint.
//I do not understand how to do this.  The code here is my latest of many attempts:
matrix.m_front.m_x = xPin;
matrix.m_front.m_y = yPin;
matrix.m_front.m_z = zPin;
//End trouble area :)

NewtonUserJoint* newHinge;

newHinge = CreateCustomHinge (&matrix[0][0], nChildBody, nParentBody);


[Stucuk]

http://en.wikipedia.org/wiki/Matrix_(mathematics)
^ Unless you like maths then that won't help.


Matrix's store the Position, Scale(Tho you generally don't touch scale) and Rotation of an Object.

Note: IIRC You don't set the pin in the matrix. Matrix iirc is just where the joint should "sit" between the 2 bodies. Tho i havn't done Joints since 1.53 .

[samisaham]

Thanks for your help!
Unless I'm greatly mistaken, the axis of allowed rotation must be set somewhere?
How would I joint a body to the world allowing it to rotate only around the z-axis, for instance?

[JernejL]

Thanks for your help!
Unless I'm greatly mistaken, the axis of allowed rotation must be set somewhere?
How would I joint a body to the world allowing it to rotate only around the z-axis, for instance?

create a unit length vector... directed at the Z axis?

[samisaham]

Sorry if I'm missing the obvious -

newHinge = CreateCustomHinge (&matrix[0][0], nChildBody, nParentBody);

How do I construct a matrix that contains both my origin of joint, and pin direction vector to pass to this function from JointLibrary.dll?

[samisaham]

ah! I think I've got it working:

Code: Select all

dVector pin(xPin,yPin,zPin);
   matrix = dgGrammSchmidt(pin);
   matrix.m_posit.m_x += xOrig;
   matrix.m_posit.m_y += yOrig;
   matrix.m_posit.m_z += zOrig;

Simple, but had to pull dgGrammSchmidt() out of 1.53 matrix implimentation

[Julio Jerez]

It is in the dMass class

[samisaham]

Thanks
My copy seriously was missing it. I must have corrupted the file somehow... I looked in the .rar and it is in there. All up and running now! Thanks for your help