LookAtMouse

Author: capnbishop

Description

This script will cause an object to rotate towards the mouse cursor along it's y axis.

This action could be good for third person games where objects need to point to the cursor but remain parallel with the ground. For instance, a sentry gun located in the center of the screen that rotates toward the mouse to target oncoming enemies.

Usage

Drop this script onto a GameObject to have it look toward the cursor. Change the speed value to alter how quickly the object rotates.

JavaScript - LookAtMouse.js

// LookAtMouse will cause an object to rotate toward the cursor, along the y axis.
//
// To use, drop on an object that should always look toward the mouse cursor.
// Change the speed value to alter how quickly the object rotates toward the mouse.
 
// speed is the rate at which the object will rotate
var speed = 4.0;
 
function Update () {
    // Generate a plane that intersects the transform's position with an upwards normal.
    var playerPlane = new Plane(Vector3.up, transform.position);
 
    // Generate a ray from the cursor position
    var ray = Camera.main.ScreenPointToRay (Input.mousePosition);
 
    // Determine the point where the cursor ray intersects the plane.
    // This will be the point that the object must look towards to be looking at the mouse.
    // Raycasting to a Plane object only gives us a distance, so we'll have to take the distance,
    //   then find the point along that ray that meets that distance.  This will be the point
    //   to look at.
    var hitdist = 0.0;
    // If the ray is parallel to the plane, Raycast will return false.
    if (playerPlane.Raycast (ray, hitdist)) {
        // Get the point along the ray that hits the calculated distance.
        var targetPoint = ray.GetPoint(hitdist);
 
        // Determine the target rotation.  This is the rotation if the transform looks at the target point.
        var targetRotation = Quaternion.LookRotation(targetPoint - transform.position);
 
        // Smoothly rotate towards the target point.
        transform.rotation = Quaternion.Slerp(transform.rotation, targetRotation, speed * Time.deltaTime);
    }
}

C# - LookAtMouse.cs

This is a direct copy of the Javascript function implemented in c#

using UnityEngine;
using System.Collections;
 
public class LookAtMouse : MonoBehaviour
{
 
	// speed is the rate at which the object will rotate
	public float speed;
 
	void FixedUpdate () 
	{
    	// Generate a plane that intersects the transform's position with an upwards normal.
    	Plane playerPlane = new Plane(Vector3.up, transform.position);
 
    	// Generate a ray from the cursor position
    	Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition);
 
    	// Determine the point where the cursor ray intersects the plane.
    	// This will be the point that the object must look towards to be looking at the mouse.
    	// Raycasting to a Plane object only gives us a distance, so we'll have to take the distance,
    	//   then find the point along that ray that meets that distance.  This will be the point
    	//   to look at.
    	float hitdist = 0.0f;
    	// If the ray is parallel to the plane, Raycast will return false.
    	if (playerPlane.Raycast (ray, out hitdist)) 
		{
        	// Get the point along the ray that hits the calculated distance.
        	Vector3 targetPoint = ray.GetPoint(hitdist);
 
        	// Determine the target rotation.  This is the rotation if the transform looks at the target point.
        	Quaternion targetRotation = Quaternion.LookRotation(targetPoint - transform.position);
 
        	// Smoothly rotate towards the target point.
        	transform.rotation = Quaternion.Slerp(transform.rotation, targetRotation, speed * Time.deltaTime);
		}
    }
}