Question by nitsnbolts_unity · Dec 10, 2020 at 01:11 PM · rotation quaternion axis eulerangles

Quaternions: Setting rotation of one gameObject to Y,Z-Axis rotation of gameObject-A and Z-Axis position of gameObject-B

I'm trying to set the rotation of a gameObject so that it's X,Y,Z rotation is based on 2 seperate gameObjects:

The Y and Z-Axis rotation is based on Y and Z-axis rotation of one gameObject.
And its X-Axis rotation is based on the Z-Axis localPosition of another gameObject.

Any idea on how to go about doing this?

What I have so far:

     Quaternion combinedQuaternion;
     GameObject mainGameObject;
     GameObject rotateAxisYZ;
     GameObject moveAxisZ;
     float xRotate, yRotate, zRotate;
     void RotateMainObject()
     {   
         // Setting x, y, z euler angle values of mainGameObject to rotateAxisYZ and moveAxisZ
         xRotate = moveAxisZ.transform.localPosition.z * 20;
         yRotate = rotateAxisYZ.transform.localEulerAngles.y;
         zRotate = rotateAxisYZ.transform.localEulerAngles.z;
         mainGameObject.transform.localEulerAngles = new Vector3(xRotate, yRotate, zRotate);

         // Combining euler angles into Quaternion form and setting it to mainGameObject rotation
         combinedQuaternion.eulerAngles = mainGameObject.transform.localEulerAngles;
         mainGameObject.transform.rotation = combinedQuaternion;
     }

This works well up to a point it seems. As long as the main gameObject is rotating on the X and Y axis alone - all's good. Once I introduce Z axis rotation - there's axis swapping and everything goes haywire. Anyone know of any possible solutions?

Add comment · Show 1

nitsnbolts_unity · Dec 10, 2020 at 12:40 PM 0

Ok, I've just solved the problem. Was working on it for days and managed to solve it a few minutes after posting haha. It was a rather simple fix. Here it is below:

  void Rotate$$anonymous$$ainObj()
     {
         Quaternion x = Quaternion.Euler(moveAxisZ.transform.localPosition.z * 100, 0, 0);
         Quaternion y = Quaternion.Euler(0, rotateAxisYZ.transform.localEulerAngles.y, 0);
         Quaternion z = Quaternion.Euler(0, 0, rotateAxisYZ.transform.localEulerAngles.z);
         Quaternion result = y * z * x;
         mainGameObject.transform.rotation = result;
     }

You can multiply the relevant floats with your input floats if need be. It was interesting to see that if the resulting quaternion was not multiplied in the order of y*z*x then the axes still do go nuts. I guess that's just the nature of matrix multiplications. Too bad it's not that intuitive. So a bit of trial and error is needed, but a very good and easy fix!