JointData creation question

What does it means "AinA" and "BinB" in this example?

Code (CSharp):

1. var jointData = JointData.CreateFixed(float3 positionAinA,
2.                                                              float3 positionBinB,
3.                                                              quaternion orientationAinA,
4.                                                              quaternion orientationBinB);

 

positionAinA is the position of body A's joint in body A's local space, and so on for the remaining arguments. For a simpler example, consider a ball and socket, which just takes a position in A and a position in B. The joint's job is to apply forces to the bodies at those points so that those positions are the same in world space. For the fixed joint, the same idea extends to orientation. If you imagine X,Y,Z axes coming out of the point in each body, the joint's job is to make A's axes line up with B's axes. So orientationAinA and orientationBandB determine which way the axes point in each body's local space.

 

So, this is code to create joint between two existing entities:

Code (CSharp):

1. var BFromWorld = math.inverse(new RigidTransform(rotationB, positionB));
2.  
3. var positionAinA = float3.zero;
4. var positionBinB = math.transform(BFromWorld, positionA); //positionA from world space to local B space
5. var orientationAinA = math.mul(math.inverse(rotationA), rotationB); //relative rotation from A to B
6. var orientationBinB = quaternion.identity;

 

That looks right to me. If you pass those to JointData.CreateFixed(), you should get a joint that maintains the bodies' current relative transform.