unity create obb by hand

create and use obb as zip.cs

	[MenuItem("Demo/Build Bundle")]
	static void Build()
	{
        BuildPipeline.BuildAssetBundles("Assets", BuildAssetBundleOptions.UncompressedAssetBundle, BuildTarget.Android);

        FileUtil.DeleteFileOrDirectory ("obb.zip");
		var obbFile = ZipFile.Create ("obb.zip");

		obbFile.BeginUpdate ();
        obbFile.Add ("Assets/bundle", CompressionMethod.Stored);
		obbFile.CommitUpdate ();
	}
  
  void Load() 
    {
		var zipFile = new ICSharpCode.SharpZipLib.Zip.ZipFile ("obb.zip");
        var entry = zipFile.GetEntry ("Assets/bundle");
        ulong fileOffset;
		using (var stream = zipFile.GetInputStream(entry)) {

            fileOffset = (ulong)stream.Seek(0, System.IO.SeekOrigin.Begin);
			Debug.Log ("entry: " + entry.Size + " " + fileOffset );
		}

        var assetBundle = AssetBundle.LoadFromFile("obb.zip", 0, fileOffset);

		var myTexture = assetBundle.LoadAsset("Image") as Texture2D;
		gameObject.GetComponent<Renderer> ().material.mainTexture = myTexture;

	}