Unity AssetBundle Sprite Atlas Duplication

Sprite Atlas Duplication

The following sections describe a quirk of Unity 5’s asset dependency calculation code when used in conjunction with automatically-generated spriteA 2D graphic objects. If you are used to working in 3D, Sprites are essentially just standard textures but there are special techniques for combining and managing sprite textures for efficiency and convenience during development. More info
See in Glossary atlases.

Any automatically-generated sprite atlasA texture that is composed of several smaller textures. Also referred to as a texture atlas, image sprite, sprite sheet or packed texture. More info
See in Glossary will be assigned to the AssetBundle containing the Sprite Objects from which the sprite atlas was generated. If the sprite Objects are assigned to multiple AssetBundles, then the sprite atlas will not be assigned to an AssetBundle and will be duplicated. If the Sprite Objects are not assigned to an AssetBundle, then the sprite atlas will also not be assigned to an AssetBundle.

To ensure that sprite atlases are not duplicated, check that all sprites tagged into the same sprite atlas are assigned to the same AssetBundle.

Unity 5.2.2p3 and older

Automatically-generated sprite atlases will never be assigned to an AssetBundle. Because of this, they will be included in any AssetBundles containing their constituent sprites and also any AssetBundles referencing their constituent sprites.

Because of this problem, it is strongly recommended that all Unity 5 projects using Unity’s sprite packerA facility that packs graphics from several sprite textures tightly together within a single texture known as an atlas. Unity provides a Sprite Packer utility to automate the process of generating atlases from the individual sprite textures. More info
See in Glossary upgrade to Unity 5.2.2p4, 5.3 or any newer version of Unity.

For projects that cannot upgrade, there are two workarounds for this problem:

1. Easy: Avoid using Unity’s built-in sprite packer. Sprite atlases generated by external tools will be normal Assets, and can be properly assigned to an AssetBundle.

2. Hard: Assign all Objects that use automatically atlased sprites to the same AssetBundle as the sprites.

   • This will ensure that the generated sprite atlas is not seen as the indirect dependency of any other AssetBundles and will not be duplicated.

   • This solution preserves the workflow of using Unity’s sprite packer, but it degrades developers’ ability to separate Assets into different AssetBundles, and forces the re-download of an entire sprite atlas when any data changes on any component referencing the atlas, even if the atlas itself is unchanged.