How to rotate an object around a fixed point so it follows the mouse cursor?

[ac566]

I want to rotate the purple rectangle around the red square in reference to the center of the square. In addition I want to be able to have the rectangle follow the mouse cursor wherever it goes. Here is a picture for demonstration:

Here is the code I have already written:

void FixedUpdate(){
		transform.RotateAround(new Vector3(0.0f, 1.25f, -12.5f), Vector3.up, Vector3.Angle(new Vector3(1f,1f,0f),new Vector3(Input.mousePosition.x,Input.mousePosition.y, 0f)));
	}

This code doesn’t work and just rotates the rectangle around the square at a fixed pace with no noticeable influence from the mouse. Thank you for your help.

[robertbu]

Here is one solution. If the center object does not move, you can move the calculation of ‘centerScreenPos’ to Start().

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {    

	public Transform center;
	private Vector3 v;


	void Start() {
		// Requires the block to be directly to the right of the center
		//   with rotation set correctly on start
		v = (transform.position - center.position);
	}
	
	void Update(){
		Vector3 centerScreenPos = Camera.main.WorldToScreenPoint (center.position);
		Vector3 dir = Input.mousePosition - centerScreenPos;
		float angle = Mathf.Atan2 (dir.y, dir.x) * Mathf.Rad2Deg;
		Quaternion q = Quaternion.AngleAxis (angle, Vector3.forward);
		transform.position = center.position + q * v;
		transform.rotation = q;
	}
}