Rotate Z axis of object to camera

Questions & Answers
1

Hello guys, I’m having trouble making all connections (3 cylinders with ball) is facing the camera. The core (central sphere) rotates according to the mouse, and when this happens connections must rotate along with the nucleus always turning the cylinders at the camera.

What happens:
alt text

What I need:
alt text

Code used in connections:

var angle;
 
function Start() {
}

function Update  () {

	var center : GameObject = GameObject.Find("centro");
	
	var dx = transform.position.x - Camera.main.transform.position.x;
	var dy = transform.position.y - Camera.main.transform.position.y;
	var radians = Mathf.Atan2(dy,dx);
	
	if(center.transform.rotation.eulerAngles.x >= center.transform.rotation.eulerAngles.z)
	{
	angle = radians * 180 / Mathf.PI - (center.transform.rotation.eulerAngles.x/2*-1);
	}
	else
	{
	angle = radians * 180 / Mathf.PI + (center.transform.rotation.eulerAngles.z/2);
	}

	var rotateZ = Mathf.LerpAngle(transform.rotation.z, angle, 0);

	transform.rotation = Quaternion.Lerp(transform.rotation, Quaternion.Euler(transform.rotation.eulerAngles.x,transform.rotation.eulerAngles.y,rotateZ),1);

}

For 50% of angles this code works. In other cases the object is in the wrong rotation.

2

For this answer, I’m going to set up a coordinate system. If this coordinate system is different from the one that you’ve implemented, then be sure to change the axes! Also, I’m assuming that Z, Y, and X are normalized.

For this answer Z will point in the long direction of the cylinders (i.e. the axis you want to rotate around), Y will point perpendicular to the plane that the cylinders are arranged in (i.e. the axis you want to point toward the camera), and X will be the remaining axis. The last vector that we’ll need is the direction the camera is facing.(camera.forward).

So, now the goal is to rotate the object around the Z axis, such that the Y vector is as closely aligned wlink textith cameraForward as it can be.

With the constraint that we can only rotate around Z, we can only make Y point somewhere along the plane that is defined by having a normal of Z. So we will project camera.forward to the plane defined by Z, and call this projected vector our Y-Target.

Lastly, we’ll need to come up with a rotation that goes from Y to Y-Target. Fortunately, there’s a built in function that does that for us!

void Update()
{	
    // Project cameraForward onto the plane, to get our target.
    Vector3 yTarget = Camera.main.transform.forward - (transform.forward * Vector3.Dot(Camera.main.transform.forward, transform.forward));
	
    // Find the needed rotation to rotate y to y-target
    Quaternion desiredRotation = Quaternion.LookRotation(transform.forward, yTarget);
	 
    // Apply that rotation
    transform.rotation = desiredRotation;
}

Edit: I had trouble getting the details right without a sample project. I created a quick sample project, implemented this code and attached it. You should be able to open and run the sample project, and see that it does what you want.

Sorry for all the back and forth!

3

void Update()
{
// Project cameraForward onto the plane, to get our target.
Vector3 yTarget = Camera.main.transform.forward - (transform.forward * Vector3.Dot(Camera.main.transform.position, transform.forward));

    // Find the needed rotation to rotate y to y-target
    Quaternion rotation = Quaternion.FromToRotation(transform.up, yTarget);
 
    // Apply that rotation
    transform.Rotate(rotation.eulerAngles, Space.Self);
}

ncallaway put incorrect code. I haven’t tested this but I think it should be correct.