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Google Play Asset Delivery (Google PAD) is the Google Play Store's solution for delivering asset packs to applications once they are installed on a device. This solution is intended for use alongside the Android App Bundle distribution format. While the App Bundle distributes a customized .apk to the end user, handling code and binaries for the initial installation, the Play Asset Delivery system provides models, textures, sounds, shaders, and other large asset files separately from the .apk. This makes it possible for apps distributed through Google Play to manage the space taken up by content by delivering content as it is needed.

For more general information about Google Play Asset Delivery, refer to the official Android documentation at https://android-developers.googleblog.com/2020/06/introducing-google-play-asset-delivery.html

Unreal Engine 4.25 and newer includes Google PAD integration through a plugin, making this system simple to implement in your own projects. This plugin provides a function library with calls for managing downloads and requesting information from the Play Asset Delivery system. UGooglePADFunctionLibrary is available in both C++ and Blueprint.

Enabling the Google PAD Plugin

The Google PAD plugin can be found in the Unreal Editor's Plugins window, under the Android section. It is enabled by default in Unreal Engine 4.25.0 and newer. To use Google PAD, you must be using Android App Bundles as your packaging format.

To fully enable the plugin, open Project Settings and navigate to Plugins > GooglePAD > Packaging . Click the Enable Plugin checkbox, and the module will be available on startup for Android projects.

If you want to use Google PAD for install-time assets, you also need to navigate to Platforms > Android > APK Packaging and disable Package Data inside APK . The main .obb file will then be delivered as an install-time asset pack automatically.

Creating Asset Packs

Asset packs for Google PAD are packaged inside Android App Bundle builds, and managed by the Google Play Store when they are uploaded. This section explains how to package and organize asset packs for inclusion in your App Bundle.

Asset Pack Delivery Modes

Chunks are Unreal Engine's format for organizing external assets. Chunk 0 represents the base installation of the game, while all other chunks are .pak files containing assets outside of the game's main installation.

To utilize Google PAD, you must group your game's assets into chunks, and you must group those chunks into asset packs based on the delivery mode you want to use for them. Google Play Asset Delivery supports the following delivery modes for asset packs:

You can create a total of 50 asset packs per application. You can only have one Install-Time and one Fast-Follow asset pack per project, but can use as many On-Demand asset packs as you want as long as you do not exceed this limit.

Creating Chunks

Open your **Project Settings and navigate to Project > Packaging and make sure Generate Chunks is enabled.

Now you can organize assets into chunks using the asset manager or primary asset labels .

You can create a primary asset label by right-clicking in the Content Browser and clicking Miscellaneous > Data Asset .

You will be prompted to pick a Data Asset Class . Select PrimaryAssetLabel , then click Select .

Name your new Primary Asset Label, then double-click it to edit its information.

Enable Label Assets in my Directory to designate all the assets in the same folder as belonging to this asset label. Set the Chunk ID to any value higher than 0 to designate which chunk the assets belonging to this label will belong to. You can also add assets directly to the asset label using the Explicit Assets list.

The Asset Manager is located in Project Settings , under Game > Asset Manager .

Here you can designate rules that your project will use to procedurally group assets into chunks. See the Cooking and Chunking page for more details.

Once you have designated which assets belong to specific chunks, packaging your project will output your chunks as .pak files. You can find them in your project folder under Saved\StagedBuilds[PlatformName][ProjectName]\Content\Paks .

Including Chunks in your App Bundle Build

Each delivery mode for Play Asset Delivery has different requirements for incorporating chunks into App Bundles.

For Install-Time assets, you do not need to make any changes.

For Fast-Follow or On-Demand assets, select the .pak files you want to include and move them to your project's Build/Android/gradle/assetpacks directory. Each delivery mode has a different subfolder:

• Fast-Follow asset packs must be placed in Build/Android/gradle/assetpacks/fast-follow/[assetpackname]/src/main/assets

• On-Demand asset packs must be placed in Build/Android/gradle/assetpacks/on-demand/[assetpackname]/src/main/assets

Replace [assetpackname] with the name of the asset pack that the chunks will be bundled into. You can create multiple different named asset packs with different sets of .pak files. However, the names of your asset packs must be unique, and they may not be re-used between fast-follow and on-demand. This name will be the one that you use when querying for asset packs with the API.

Finally, you need to add a build.gradle file in the asset pack folder containing the following code:

apply plugin: 'com.android.asset-pack'

def fileparts = projectDir.absolutePath.replaceAll('\\\\', '/').tokenize('/')
def assetPackName = fileparts[fileparts.size()-1]
def assetPackType = fileparts[fileparts.size()-2]

assetPack {
    packName = assetPackName
    dynamicDelivery {
        deliveryType = assetPackType
        instantDeliveryType = assetPackType
    }
}

After you have met these requirements, package the project as an app bundle again, and it will include each of these asset packs in your build. When you upload the App Bundle to the Google Play Store, the asset packs will be available for download using the Google PAD API.

Excluding Chunks From the OBB File

By default, .pak files are included in the OBB file generated alongside your project. To exclude them, you need to open your DefaultEngine.ini file and filter them using OBB filters under Android Runtime Settings.

[/Script/AndroidRuntimeSettings.AndroidRuntimeSettings]
+ObbFilters="-*pakchunk1*"
+ObbFilters="-*pakchunk2*"
+ObbFilters="-*pakchunk3*"
+ObbFilters="-*pakchunk4*"
+ObbFilters="-*pakchunk5*"
+ObbFilters="-*pakchunk6*"
+ObbFilters="-*pakchunk7*"
+ObbFilters="-*pakchunk8*"
+ObbFilters="-*pakchunk9*"

In the example above, the OBB filters will catch any .pak files containing any of the text provided. For instance, +ObbFilters="-*pakchunk1*" will omit any pak file whose name contains "pakchunk1".

API Reference

The following sections detail the available functions in the Google PAD function library and their usage.

Requests and Error Handling

All requests in the Google PAD function library return an EGooglePADErrorCode denoting whether or not the operation succeeded and, if not, what specific error prevented the request from being completed. The possible error codes are as follows:

In addition to this return value, request functions will have an out variable providing the requested information. If you get a result of AssetPack_NO_ERROR , you can proceed with the provided information normally. Otherwise, you should use flow control to react to the provided error code appropriately.

Getting the Location of Downloaded Files

The function GetAssetPackLocation fetches the location of an asset pack that has been downloaded and caches information about it locally. If the asset is available, it will output an integer handle that can be used to access the cached information as needed.

Calling GetAssetsPath and providing the location handle will output a string with the asset path for the desired asset pack. GetStorageMethod will output an EGooglePADStorageMethod stating the way the asset pack is stored on the user's device. Once you know the asset path and storage method, you can then use appropriate calls to access the assets.

The possible storage methods are as follows:

Once you are done using the above information, you must pass the location handle to ReleaseAssetPackLocation to free the cached location info.

If GetAssetPackLocation returns an error code of AsetPack_UNAVAILABLE or AssetPack_DOWNLOAD_NOT_FOUND , then the desired asset pack is unavailable and must be downloaded.

Requesting Information about Asset Packs

The function RequestInfo takes in a TArray of asset pack names and returns an EGooglePADErrorCode denoting their current status. RequestInfo is not required to initiate a download, but can be used to determine whether remote asset packs are valid.

Requesting or Cancelling a Download

The function RequestDownload takes in a TArray of strings representing the names of the asset packs you would like to download, then sends a request to the remote service to begin downloading those asset packs. If RequestDownload shows no errors, the asset packs will be downloaded and transferred to the app asynchronously in the background.

Because this functionality is asynchronous, the RequestDownload function does not return information about the downloaded asset pack, other than an error code denoting whether the request was successful. You must use the functions detailed in the Monitoring Download Status section below to check for the download's current status, and to access the asset pack itself you must use GetAssetPackLocation once the download is complete.

The function CancelDownload also uses a list of asset pack names, and will cancel downloading the designated asset packs.

Getting Cellular Data Status

The function ShowCellularDataConfirmation will prompt the user for whether they want to download data using their cellular network. If the prompt is already present, you can use GetShowCellularDataConfirmationStatus to return an EGooglePADCellularDataConfirmStatus stating whether or not the user has approved the download.

Results of AssetPack_CONFIRM_UNKNOWN and AssetPack_CONFIRM_PENDING mean the user has not given approval yet, and the application should stand by until approval is given.

A result of AssetPack_CONFIRM_USER_CANCELLED means that the user has chosen not to allow the use of cellular data, and downloads should not be permitted at this time.

A result of AssetPack_CONFIRM_USER_APPROVED means that the user has given express approval to use cellular data and downloads should be allowed to proceed. Additionally, If this function returns an EGooglePADErrorCode with a result of AssetPack_NETWORK_UNRESTRICTED , the user is on their wi-fi network and does not need to use cellular data, therefore downloads should be permitted without the need to continue checking this function.

Monitoring Download Status

GetDownloadState will locally cache the download status of an asset pack and return a download handle providing access to the cached information. This function takes in the name of the asset pack that you want to download and outputs the handle as an integer. You should keep the download handle cached so that you can continue to monitor the download, otherwise, you will need to re-acquire it.

With a valid download handle, you can call GetDownloadStatus to return the status of the desired asset pack as an EGooglePADDownloadStatus . This enum represents the status of a download as one of several possible states, which are as follows:

You can also use the download state handle to call GetBytesDownloaded , which will return the number of bytes currently downloaded to the user's device, and GetTotalBytesToDownload , which will return the total target size of the download.

Once you have finished using the download status information, you must call ReleaseDownloadState and provide the handle to release the cached download information from memory.

Removing Asset Packs

The function RequestRemoval takes in an asset pack name and removes the specified asset pack from the user's device asynchronously. The asset pack's removal status can be monitored with GetDownloadStatus as above.

Recommended Implementation

Implementation of the Google PAD API can be modeled as a cycle of different states for each download.

Implementing your solution in a custom GameState class will enable you to track a download continuously even as you change scenes and game modes. Alternatively, you may want to implement your solution in a front-end game mode that loads on startup so that you can perform necessary patches and updates before starting the game. The exact details of your solution will depend on your project's specific needs for updating assets.