Bevy AssetIO Plugin For Reading Optionally Obfuscated Zips

[zicklag]

Hey everybody! I just released a Bevy plugin that allows you to bundle your assets for your game in an optionally obfuscated zip file: bevy_assetio_zip.

The obfuscated zip option will scramble the bits of the asset zip by XOR-ing the bytes to make it unrecognizable without XOR-ing it again. It is no real protection, but it does prevent the casual user from being able to recognize the asset format. The plugin by default will read assets from either an assets.zip or an assets.bin file and will fall back to the default bevy asset loader if it can't find an asset in the bundle.

Usage

Simply enable the plugin when setting up your Bevy app to enable loading from asset bundle
files.

App::build()
    // Any config must be inserted before adding plugins. This is optional.
    .add_resource(AssetIoZipConfig {
        // The name of the asset bundle file, excluding the extension, to load
        file_name: "assets".into(), // This is the default
    })
    // Add the default plugins
    .add_plugins_with(DefaultPlugins, |group| {
        // With our additinoal asset IO plugin
        group.add_before::<bevy::asset::AssetPlugin, _>(AssetIoZipPlugin)
    })
    .run();

Once enabling the plugin, the game will now search for assets.zip and assets.bin files
adjacent to the executable when attempting to load assets. If an asset is not found in the zip
file, it will attempt to load the asset using the default Bevy asset loader for the target
platform.

Types of Asset Bundles

There are two kinds of asset bundle files supported by this plugin, plain .zip files and
obfuscated zip files ( which have a .bin extension ). Plain .zip files are typical zip files
that can be created with normal zip software. Obfuscated zip files can be created with
[bevy_assetio_zip_bundler] and are simply a normal zip file that has had the bytes XOR-ed by
0b01010101.

⚠️ WARNING: Obfuscated zip files provide no real security or protection for your assets.
It is trivial to decript the asset bundle even if it is obfuscated. Obfuscation of the zip is
only a measure to prevent casual users from being able to immediately introspect the data.

Bundling Assets

To bundle your bevy assets you can use the [bevy_assetio_zip_bundler] crate. The easiest way
to use it is to add this to your build.rs file:

fn main() {
    bevy_assetio_zip_bundler::bundle_crate_assets();
}

This will automatically zip up your crate's assets folder and put it in your target/ dir
when compiling release builds. When distributing your application simply take your asset bundle
and place it adjacent to the executable and Bevy will attempt to load assets from the bundle
before falling back to the assets dir.

You can configure the name, obfuscation, and compression of the bundle by creating and
asset_config.toml file next to your Cargo.toml file:

# Bundle assets even for debug builds
bundle-for-debug-builds = true # Default: false

# Obfuscate assets. This doesn't protect from reverse-engineering, but it makes it a little harder
# for the average user to read them.
obfuscate = true # Default: false

# Compress the asset bundle using Bzip2 compression. Other options are "deflate" and "none".
compression = "bzip2" # Default: "bzip2"

# The name of the file, not counting the exention, which will be different based on the `obfuscate`
# setting. Obfuscated bundles will end in `.bin` and non-obfuscated bundles will end in `.zip`.
file-name = "assets" # Default: "assets"

# Set the directory that asset bundle should be placed.
out-dir = "../target" # Default "./target"

Alternatively, if you want to create your own tooling or customize the asset bundling process,
you can manually bundle the assets using the bevy_assetio_zip_bundler::bundle_assets
function.