App slicing

App slicing allows you to dynamically download Assets according to the specification of the device the application is running on. For example, app slicing can download high-resolution Assets for larger devices and low-resolution Assets for smaller devices. App slicing works by defining AssetBundles, with the added provision of variants. You can decide which variant to use at startup and automatically append this to the Asset file name upon download.

Create a variant

To create a variant, use the following steps:

1. Click on your AssetBundle folder and navigate to the Asset Labels section at the bottom of the InspectorA Unity window that displays information about the currently selected GameObject, asset or project settings, allowing you to inspect and edit the values. More info
   See in Glossary window.
2. Click on the right-hand drop-down menu, select New, and enter the name of your new variants. AssetBundle variants must be lowercase.
3. Create a new script in the Unity Editor folder called BuildiOSAppSlices.cs.
4. Copy and paste the following code, replacing the example label textures and variants hd and sd with your own. In this code example, multiple folders are referenced: one containing HD textures and one containing SD textures. These folders have been given the variants hd and sd.

using UnityEngine;
using UnityEditor;


public class BuildiOSAppSlices : MonoBehaviour
{
    [InitializeOnLoadMethod]
    static void SetupResourcesBuild( )
    {
        UnityEditor.iOS.BuildPipeline.collectResources += CollectResources;
    }

    static UnityEditor.iOS.Resource[] CollectResources( )
    {
        return new UnityEditor.iOS.Resource[]
        {
            new UnityEditor.iOS.Resource("textures").BindVariant( "Assets/ODR/textures.hd", "hd" )
                                     .BindVariant( "Assets/ODR/textures.sd", "sd" )
                     .AddOnDemandResourceTags( "textures" ),
    };
    }

    [MenuItem( "Bundle/Build iOS App Slices" )]
    static void BuildAssetBundles( )
    {
        var options = BuildAssetBundleOptions.None;

        bool shouldCheckODR = EditorUserBuildSettings.activeBuildTarget == BuildTarget.iOS;

#if UNITY_TVOS
            shouldCheckODR |= EditorUserBuildSettings.activeBuildTarget == BuildTarget.tvOS;
#endif

        if( shouldCheckODR )
        {
#if ENABLE_IOS_ON_DEMAND_RESOURCES
            if( PlayerSettings.iOS.useOnDemandResources )
                options |= BuildAssetBundleOptions.UncompressedAssetBundle;
#endif

#if ENABLE_IOS_APP_SLICING
            options |= BuildAssetBundleOptions.UncompressedAssetBundle;
#endif
        }

        BuildPipeline.BuildAssetBundles( "Assets/ODR", options, EditorUserBuildSettings.activeBuildTarget );
    }

}

This code creates a new menu in the Unity Editor menu bar called Bundle. Click this and select Build iOS App Slices. This generates the AssetBundles in the ODR folder.

Load an asset

To load an Asset, create a script file named LoadBundle.cs in your Assets folder and copy in the following code. Replace textures with the name of the variant you want to load.

using UnityEngine;
using UnityEngine.iOS;
using System;
using System.Collections;

public class LoadBundle : MonoBehaviour
{
    public AssetBundle     TextureBundle;


    void Start( )
    {
        LoadAssetAsync( "textures", "textures" );
    }

    public IEnumerator LoadAsset( string resourceName, string odrTag )
    {
        // Create the request
        using(OnDemandResourcesRequest request = OnDemandResources.PreloadAsync( new string[] { odrTag } ))
        {
            // Wait until request is completed
            await request;

            // Check for errors
            if( request.error != null )
                throw new Exception( "ODR request failed: " + request.error );

            TextureBundle = AssetBundle.LoadFromFile( "res://" + resourceName );

        }
    }
}

Modify a variant

There might be times where you want to use a variant on a specific device, or on devices that run over a set memory limit. To do this, you can change the settings of each variant you use.

To modify a variant, navigate to Player Settings > Other Settings > Configuration and expand Variant map for app slicing.

Note: Enable Use on demand resources in Player Settings > Other > Configuration to view the Variant map for app slicing options.

Additional resources

• On-demand resources