Packed Sprite Atlas in AssetBundle

Symptoms 

• AssetBundles with sprites have a greater size than the expected.
• Atlas is stored twice in AssetBundles

Cause

Issue #1

Before Unity 5.2.2p4, there was a bug using Sprite Atlas and AssetBundles. Let us consider that you want to create two asset bundles:

• Three sprites are tagged into an atlas and packed in an AssetBundle. ("art.unity3d")
• A sprite using the same atlas and packed in a different AssetBundle. ("prefab.unity3d")

When you create the AssetBundles, the "art.prefab" will contain the corresponding sprite vertices, a pointer to the atlas and the atlas texture. The second prefab will also store (duplicate) the atlas texture.

Issue #2:

Another issue is when the user marks one of the sprites to be in another AssetBundle. The other AssetBundle will also contain the atlas image.

Resolution

Issue #1:

• Update to Unity 5.2.2p4, or the latest Unity version.

Issue #2:

• Sprites packed into the same Atlas needs to be packed in the same AssetBundle.

The below image shows two sprites using the same AssetBundle and Packing tag. 

The example below checks if the sprites tagged in the same atlas are packed in different bundles:

public class SpriteChecker 
{
    // This will create a Menu named "Support", with a sub-menu 
    // named "SpriteChecker", in the Editor menu bar.
    [MenuItem("Support/SpriteChecker")]
    static void CheckSpritesTagsAndBundles () 
    {
        // Get all the GUIDs (identifiers in project) of the Sprites in the Project
        string[] guids = AssetDatabase.FindAssets ("t:sprite");

        // Dictionary to store the tags and bundle names
        Dictionary<string,string> dict = new Dictionary<string, string>();
        foreach( string guid in guids) 
        {
            string path = AssetDatabase.GUIDToAssetPath(guid);
            TextureImporter ti = TextureImporter.GetAtPath( path) as TextureImporter;

            // If the tag is not in the dictionary, add it
            if (!dict.ContainsKey (ti.spritePackingTag ))
                dict.Add(ti.spritePackingTag, ti.assetBundleName);
            else
                // If the tag is associated with another bundle name, show an error
                if (dict[ti.spritePackingTag] != ti.assetBundleName)
                    Debug.LogWarning("Sprite : " + ti.assetPath + " should be packed in "+  dict[ti.spritePackingTag] );
        }
    }
}

More Information

http://docs.unity3d.com/Manual/Sprites.html

http://docs.unity3d.com/Manual/AssetBundlesIntro.html