Unity can use Asset Bundles for loading assets to be used in the game.
This has the benefit of lowering the load-times of the game as it avoids loading each texture/sound/asset separately and instead only load one bundle.
The data in the bundle is also compressed in a very effective way usually making the bundle size about half of the original file size.
Referencing files in the bundle is done the same way as when they are separate files since the bundle contains the path the files were in when imported.
Bundles are version specific to the Unity-version they were created with so bundles created for RimWorld 1.6 onwards are built in 2022.3 and cannot be used in earlier versions of the game.
If your mod has version-support you will need to use LoadFolders.xml to have older versions use older bundles or the actual textures/sounds-folders
Files loaded from the Textures/Sounds folders will override any files in AssetBundles so be sure to exclude these folders from loading if using AssetBundles.
It is a good idea to use Asset Bundles when the total amount of asset files are above 10.
Here is a chart showing the increase in load-times with different amounts of textures in various sizes:
Install Unity 2022.3 as well as Unity HUB
Place asset content in Assets/Data in a folder with the mod-identifier as a name
Use the project-script to generate an asset bundle to be placed in your mod
The bundle can include Textures and Sounds but not custom shaders or other advanced types as these require a separate bundle for each operatingsystem (Windows, MacOS, Linux)
To verify that the bundle has the correct files with the correct paths, use a tool like Asset Studio
NOTE 1: Asset bundle files has to have a unique name due to a limitation in Unity
NOTE 2: Terrain textures are imported in a different way so if you have terrain-textures, be sure to place them in a path that has folder named "terrain" for the script to know its a terrain-texture.
Mod has the identifier author.modname
This projects path is c:\Asset Builder
Copy the whole Textures-folder to c:\Asset Builder\Assets\Data\author.modname\
Run Unity in batch mode with:
"C:\Program Files\Unity 2022.3.61f1\Editor\Unity.exe" -batchmode -quit -projectPath="c:\Asset Builder" -executeMethod ModAssetBundleBuilder.BuildBundles --assetBundleName=author_modname
The bundle should then be found in c:\Asset Builder\Assets\AssetBundles
Copy the author_modname and author_modname.manifest files to an AssetBundles-folder in the mod