Rotating 2D square in 3D space around the Y axis

Unity Engine
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1

The core of what I’m attempting to do is create a 2D square (points across X and Y axis), and rotate it around the Y axis. So only their X and Z values should be changing, their Y value should be stationary.

Here’s my attempt:

    private void CalculateSquarePosition(Vector3 pos, Vector3 rot)
    {
        // Set Dimensions
        float squareX = squareDimensions.x / 2;
        float squareY = squareDimensions.y / 2;

        //calculate position
        Vector3 cornerPos1 = new Vector3(pos.x + squareX, pos.y + squareY, pos.z);
        Vector3 cornerPos2 = new Vector3(pos.x - squareX, pos.y + squareY, pos.z);
        Vector3 cornerPos3 = new Vector3(pos.x + squareX, pos.y - squareY, pos.z);
        Vector3 cornerPos4 = new Vector3(pos.x - squareX, pos.y - squareY, pos.z);

        //calculate rotation
        Vector3 cornerRot1 = CalculateRotation(cornerPos1, rot);
        Vector3 cornerRot2 = CalculateRotation(cornerPos2, rot);
        Vector3 cornerRot3 = CalculateRotation(cornerPos3, rot);
        Vector3 cornerRot4 = CalculateRotation(cornerPos4, rot);

        //final position (this is just a place holder, but don't i need to do something here?)
        Vector3 corner1 = cornerRot1;
        Vector3 corner2 = cornerRot2;
        Vector3 corner3 = cornerRot3;
        Vector3 corner4 = cornerRot4;


        Debug.DrawLine(corner2, corner1, Color.white);
        Debug.DrawLine(corner1, corner3, Color.white);
        Debug.DrawLine(corner3, corner4, Color.white);
        Debug.DrawLine(corner4, corner2, Color.white);
    }

    private Vector3 CalculateRotation(Vector3 position, Vector3 rotation)
    {
        //2d translate rotation = ((x * cos(rot) - y * sin(rot), (x * sin(rot) - y *  cos(rot))

        float rot = rotation.y;
        float posX = position.x;
        float posZ = position.z;

        Vector3 rotatedPosition = new Vector3(posX * Mathf.Cos(rot) - posZ * Mathf.Sin(rot), rot, posX * Mathf.Sin(rot) - posZ * Mathf.Cos(rot));

        return rotatedPosition;
    }

I honestly have no clue what I’m doing wrong, but I’m pretty sure it’s something in here

2 
        private void CalculateSquarePosition(Vector3 pos, Vector3 rot)
        {
            // Set Dimensions
            float squareX = squareDimensions.x / 2;
            float squareY = squareDimensions.y / 2;
    
            //calculate position
            Vector3 corner1 = new Vector3(pos.x + squareX, pos.y + squareY, pos.z);
            Vector3 corner2 = new Vector3(pos.x + squareX, pos.y - squareY, pos.z);
            Vector3 corner3 = new Vector3(pos.x - squareX, pos.y - squareY, pos.z);
            Vector3 corner4 = new Vector3(pos.x - squareX, pos.y + squareY, pos.z);
    
            //calculate rotation
            corner1 = CalculateRotation(corner1, rot);
            corner2 = CalculateRotation(corner2, rot);
            corner3 = CalculateRotation(corner3, rot);
            corner4 = CalculateRotation(corner4, rot);
    
            Debug.DrawLine(corner1, corner2, Color.white);
            Debug.DrawLine(corner2, corner3, Color.white);
            Debug.DrawLine(corner3, corner4, Color.white);
            Debug.DrawLine(corner4, corner1, Color.white);
        }
    
        private Vector3 CalculateRotation(Vector3 position, Vector3 rotation)
        {
            Vector3 rotatedPosition = Quaternion.Euler(rotation)*position;
            return rotatedPosition;
        }
3

This worked flawlessly, all I had to do afterwards was make the Vector3 entered into the “pos” parameter a local position, and then move it to its global position at that “final position” spot (I don’t want it following the position of the GO its attached to)

I greatly appreciate the help, and if it wouldn’t be a bother, could you provide a link to something that would help me better understand quaternion rotations? I’ve tried looking myself, however I’m never able to wrap my head around any of it

4

Don’t worry about understanding quaternions. Many people use cars everyday and yet they don’t have a clue on how they work. They just know how to use them.

Well just know that if you multiply a vector by a quaternion then the vector will be rotated.

Personally I went from initially finding quaternions very puzzling to eventually understanding how they worked. But then I later realized I didn’t really understand how they worked.

Maybe one day I’ll understand how they work again. But then maybe I’ll only think I know how they work…

I’m now at the stage where I just use them and abuse them. If a thing rotates when I want it to rotate then I’m happy…

5

Thank you for replying, I truly appreciate the advice and expect to keep it in mind going forward. I suppose it makes sense considering that’s how I’ve come to understand other concepts while learning unity. Exposure seems to allow for better understanding than memorizing rules, I often find

6

To be clear though, this is nothing to do with physics, it’s just using Transforms so I’ll move this thread to scripting. Physics is when you use the physics systems!