A simple free camera script for Unity3d

SimpleFreeCamera.cs

using UnityEngine;

public class SimpleFreeCamera : MonoBehaviour
{
    [SerializeField] private float normalSpeed = 10f;
    [SerializeField] private float shiftSpeed = 15f;
    [SerializeField] private float rotateSpeed = 200f;

    private bool _lockMouse;
    private float _moveSpeed;
    private Vector2 _rotation = Vector2.zero;

    private void Update()
    {
        // check for activate and deactivate input
        if (Input.GetMouseButtonDown(1)) Activate();
        if (Input.GetMouseButtonUp(1)) Deactivate();

        if (_lockMouse)
        {
            // rotate camera
            float xDelta = Input.GetAxis("Mouse X");
            float yDelta = Input.GetAxis("Mouse Y");
            UpdateRotation(xDelta, yDelta);
        }

        // update moveSpeed
        _moveSpeed = Input.GetKey(KeyCode.LeftShift) || Input.GetKey(KeyCode.RightShift)
            ? shiftSpeed
            : normalSpeed;

        // move player
        float horizontal = Input.GetAxis("Horizontal");
        float vertical = Input.GetAxis("Vertical");
        UpdateLocation(horizontal, vertical);
    }

    private void UpdateRotation(float xDelta, float yDelta)
    {
        // loop x values after full rotation
        _rotation.x = (_rotation.x + xDelta * Time.deltaTime * rotateSpeed) % 360;
        // prevent over rotation on y axis
        _rotation.y = Mathf.Clamp(_rotation.y - yDelta * Time.deltaTime * rotateSpeed, -90, 90);
        // apply rotation to the transform
        transform.rotation = Quaternion.Euler(_rotation.y, _rotation.x, 0);
    }

    private void UpdateLocation(float horizontal, float vertical)
    {
        // create variables to control movement
        Transform t = transform;
        Vector3 moveVector = Vector3.zero;

        // add horizontal and vertical movement
        moveVector += t.right * horizontal;
        moveVector += t.forward * vertical;

        // adjust movement vector to stop faster diagonal movement
        if (moveVector.magnitude > 1) moveVector.Normalize();

        // apply movement to transform
        t.position += moveVector * Time.deltaTime * _moveSpeed;
    }

    private void Activate()
    {
        _lockMouse = true;
        Cursor.visible = false;
        Cursor.lockState = CursorLockMode.Confined;
    }

    private void Deactivate()
    {
        _lockMouse = false;
        Cursor.visible = true;
        Cursor.lockState = CursorLockMode.None;
    }
}