TexturePackingOnDemand.cs

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

/* by FVS - HaLuan */

/// <summary>
/// Run:
/// 1. Add this script to a GameObject
/// 2. Have an internet connection
/// 3. Play
/// 4. Watch Inspector window for result
/// 5. After the Atlas showed up, change Show Sprite Index value to see difference
/// </summary>

public class TexturePackingOnDemand : MonoBehaviour
{
    string[] imageSources =
    {
           "https://upload.wikimedia.org/wikipedia/en/thumb/0/02/Homer_Simpson_2006.png/212px-Homer_Simpson_2006.png",
           "https://upload.wikimedia.org/wikipedia/en/0/0b/Marge_Simpson.png",
           "https://upload.wikimedia.org/wikipedia/en/a/aa/Bart_Simpson_200px.png",
           "https://upload.wikimedia.org/wikipedia/en/9/9d/Maggie_Simpson.png",
           "https://upload.wikimedia.org/wikipedia/en/e/ec/Lisa_Simpson.png"
    };

    [SerializeField]
    List<Texture2D> textures = new List<Texture2D>();

    [SerializeField]
    Texture2D atlas;

    [SerializeField]
    int showSpriteIndex = 0;

    Rect[] spriteRects;

    SpriteRenderer spriteRenderer;

    // Use this for initialization
    IEnumerator Start()
    {
        // Load texture
        for (int i = 0; i < imageSources.Length; i++)
        {
            ///
            WWW www = new WWW(imageSources[i]);
            while (!www.isDone)
            {
                yield return null;
            }

            ///
            if (www.texture != null)
            {
                textures.Add(www.texture);
                Debug.Log(i + " texture(s) loaded");
            }
            
        }

        // Pack
        atlas = new Texture2D(2048, 2048);
        spriteRects = atlas.PackTextures(textures.ToArray(), 2);

        // Add Sprite render component
        spriteRenderer = GetComponent<SpriteRenderer>();
        if (spriteRenderer == null)
        {
            spriteRenderer = gameObject.AddComponent(typeof(SpriteRenderer)) as SpriteRenderer;
        }

        ///
        yield return null;        
    }

    // Update is called once per frame
    void Update()
    {
        if ((atlas != null) && (showSpriteIndex < spriteRects.Length) && (showSpriteIndex >= 0))
        {
            Vector2 position = new Vector2(spriteRects[showSpriteIndex].xMin * atlas.width, spriteRects[showSpriteIndex].yMin * atlas.height);
            Vector2 size = new Vector2(spriteRects[showSpriteIndex].width * atlas.width, spriteRects[showSpriteIndex].height * atlas.height);
            spriteRenderer.sprite = Sprite.Create(atlas, new Rect(position, size), Vector2.zero);
        }
    }
}