How can character's body be continuously rotated when its head is already turned by 60°`?

Question

After some experimenting I parented an empty (HeadCam) to the character's neck. This snippet allow rotation of the head synchronously to the CardboardHead/Camera.

void LateUpdate() {
    neckBone.transform.rotation = Camera.transform.rotation *  Quaternion.Euler( 0,0,-90);
    Camera.transform.position = HeadCam.transform.position;
}

The character's arms shouldn't move when only the head rotates as long in the range -60° to 60° after that I would like to move the whole character with the arms still visible. The following method works as long the character isn't rotated by more than 180° after that the characters flips by 180° how could I achieve constant rotation?

void LateUpdate() {
    Quaternion camRot = Camera.transform.rotation * Quaternion.Euler( 0,0,-90);                 
    neckBone.transform.rotation = camRot;
    float yrot = camRot.eulerAngles.y;
    float ydelta = 0;
    if ( yrot < 300f && yrot > 180 ) {
        ydelta = yrot - 300f;
    }
    if ( yrot > 60f && yrot < 180 ) {
        ydelta = yrot - 60;
    }
    playerObj.transform.rotation =  Quaternion.Euler(0, ydelta, 0); 
    Camera.transform.position = HeadCam.transform.position;
}

A java applet for testing the algorithm standalone: https://github.com/3dbug/blender/blob/master/HeadCamRot.java

Answer 1

One possible solution would be:

// Transform of the full body of the character.
Transform body;
// Transform of the head (child of |body| component).
Transform head;
// Maximum delta angle in degrees.
float maxAngle = 60.0f;

void RotateCharacter(Quaternion target) {
  // Rotate head as much as possible without exceeding the joint angle.
  head.rotation = Quaternion.RotateTowards (body.rotation, target, maxAngle);
  // Complete the remainder of the rotation by body.
  body.rotation = target * Quaternion.Inverse (head.localRotation);
}

Please keep in mind that you might need to limit non-horizontal rotations beforehand, i.e., I assumed given x & z angles of the passed rotation won't exceed maxAngle. Besides, even so, it should be quite straightforward to add that limitation as well inside the function above if needed.

Hope it helps.

Answer 2

Finally I found a solution for this:

private float bodyRot = 0F;
private float FOV = 70f;

void LateUpdate() {
    if ( neckBone != null ) {
        Quaternion camRotQ = CameraFacing.transform.rotation * Quaternion.Euler( 0,0,-90);
        neckBone.transform.rotation = camRotQ;
        float camRot = camRotQ.eulerAngles.y;

        float delta = camRot- bodyRot;
        if ( delta > 180 ) {
            delta -= 360;
        }
        if ( delta < -180 ) {
            delta += 360;
        }
        if ( Math.Abs(delta) > FOV ) {
            if ((delta > FOV || delta < -180) && delta < 180) {
                bodyRot = camRot - FOV;
            }
            delta = camRot- bodyRot;
            if ((delta < FOV || delta > 180 ) ) {
                bodyRot = camRot + FOV;
            }
        }
        playerObj.transform.rotation =  Quaternion.Euler(0, bodyRot, 0); 
        CameraFacing.transform.position = cameraMount.transform.position;
    }
}