using UnityEngine;
using System.Collections;

public class ParalaxScrolling : MonoBehaviour
{
    public Transform[] backgrounds;                // Array of all the backgrounds to be parallaxed.
    public float parallaxScale;                    // The proportion of the camera's movement to move the backgrounds by.
    public float parallaxReductionFactor;        // How much less each successive layer should parallax.
    public float smoothing;                        // How smooth the parallax effect should be.

    private Transform cam;                        // Shorter reference to the main camera's transform.
    private Vector3 previousCamPos;                // The postion of the camera in the previous frame.


    void Awake()
    {
        // Setting up the reference shortcut.
        cam = Camera.main.transform;
    }


    void Start()
    {
        // The 'previous frame' had the current frame's camera position.
        previousCamPos = cam.position;
    }


    void Update()
    {
        // The parallax is the opposite of the camera movement since the previous frame multiplied by the scale.
        float parallax = (previousCamPos.x - cam.position.x) * parallaxScale;

        // For each successive background...
        for (int i = 0; i < backgrounds.Length; i++)
        {
            // ... set a target x position which is their current position plus the parallax multiplied by the reduction.
            float backgroundTargetPosX = backgrounds[i].position.x + parallax * (i * parallaxReductionFactor + 1);

            // Create a target position which is the background's current position but with it's target x position.
            Vector3 backgroundTargetPos = new Vector3(backgroundTargetPosX, backgrounds[i].position.y, backgrounds[i].position.z);

            // Lerp the background's position between itself and it's target position.
            backgrounds[i].position = Vector3.Lerp(backgrounds[i].position, backgroundTargetPos, smoothing * Time.deltaTime);
        }

        // Set the previousCamPos to the camera's position at the end of this frame.
        previousCamPos = cam.position;
    }
}