OrderInLayerController

using UnityEngine;
using System.Collections;

public class OrderInLayerController : MonoBehaviour
{
    SpriteInfo[] spriteInfos;
    public Transform bottom;
    void Start()
    {
        SpriteRenderer[] spriteRenderers = LayerHelper.GetSpriteRenderers(transform);    //GetComponentsInChildren<SpriteRenderer>();
        int minOrder = int.MaxValue;
        int maxOrder = int.MinValue;

        if (spriteRenderers != null && spriteRenderers.Length > 0)
        {
            foreach (var item in spriteRenderers)
            {
                if (item.sortingOrder < minOrder)
                    minOrder = item.sortingOrder;

                if (item.sortingOrder > maxOrder)
                    maxOrder = item.sortingOrder;
            }
        }
        else
        {
            Debug.LogError("Sprite renderers is empty or null");
            enabled = false;
            return;
        }


        spriteInfos = new SpriteInfo[spriteRenderers.Length];

        for (int i = 0; i < spriteRenderers.Length; i++)
        {
            int offset = spriteRenderers[i].sortingOrder - minOrder; // method in question
            spriteInfos[i] = new SpriteInfo(spriteRenderers[i], offset);
        }

        //SetDepth(10);
    }

    void Update()
    {
        SetDepth(bottom.position.y);
    }

    void SetDepth(float y)
    {
        int lowestOrder = Mathf.RoundToInt(-y * 10);

        if(spriteInfos == null || spriteInfos.Length <= 0)
        {
            Debug.LogError("SpriteInfos is empty!");
            return;
        }

        for (int i = 0; i < spriteInfos.Length; i++)
        {
            spriteInfos[i].spriteRenderer.sortingOrder =
                lowestOrder + spriteInfos[i].orderInLayerOffset;
        }
    }
}

public class SpriteInfo
{
    public SpriteRenderer spriteRenderer;
    public int orderInLayerOffset;

    public SpriteInfo(SpriteRenderer spriteRenderer, int orderInLayerOffset)
    {
        this.spriteRenderer = spriteRenderer;
        this.orderInLayerOffset = orderInLayerOffset;
    }
}