When defining AssetBundles there are a few rules to be aware of:
Beyond those rules you are free to assign any asset to any bundle you desire. However, there are certain strategies to consider when setting up your bundles.
Logical Entity Grouping is a strategy you can use to decide how to organize what goes into each of your project’s AssetBundles. The principle is to base your decisions on the functional portion of the project that each piece of content represents. This includes sections such as User-Interface, characters, environments, and anything else that may appear frequently throughout the lifetime of the application.
Organizing your AssetBundles by Logical Entity Grouping is ideal for downloadable content (DLC), because it allows you to more easily make small changes to your project which don’t require your users to re-download large amounts of additional, unchanged, assets.
The biggest trick to being able to properly implement this strategy is that the developer assigning assets to their respective bundles must be familiar with precisely when and where each asset will be used by the project.
Type Grouping is a strategy where you assign assets of similar type, such as audio tracks or language localization files, to a single AssetBundle.
Type grouping can be useful to establish AssetBundles that change rarely. Grouping AssetBundles this way may result in fewer AssetBundles changing and requiring distribution when an incremental build is done. The downside is that more AssetBundles may need to be downloaded and loaded to assemble all dependent objects together at runtime.
Concurrent Content Grouping is the idea that you will bundle assets together that will be loaded and used at the same time. You could think of these types of bundles as being used for a level based game where each level contains totally unique characters, textures, music, etc. You would want to be absolutely certain that an asset in one of these AssetBundles is only used at the same time the rest of the assets in that bundle are going to be used. Having a dependency on a single asset inside a Concurrent Content Grouping bundle would result in significant increased load times. You would be forced to download the entire bundle for that single asset.
The most common use-case for Concurrent Content Grouping bundles is for bundles that are based on scenes. In this assignment strategy, each scene bundle should contain most or all of that scenes dependencies.
Note: When building an AssetBundle containing a Scene, any Assets referenced by that Scene will also be automatically included in the AssetBundle, unless those Assets are explicitly assigned to a different AssetBundle. This is convenient when doing Concurrent Content Grouping, but you need to keep an eye out for duplicated assets if any referenced assets are also used by other scenes that you are building into separate AssetBundles.
A project absolutely can and should mix these strategies as your needs require. Using the optimal asset assignment strategy for any given scenario greatly increases efficiency for any project.
For example, a project may decide to group its User-Interface (UI) elements for different platforms into their own Platform-UI specific bundle but group its interactive content by level/scene.
Regardless of the strategy you follow, here are some additional tips that are good to keep in mind across the board:
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