Prepare Sprite Packer Legacy packed assets to work after deprecation

This page provides the scriptsA piece of code that allows you to create your own Components, trigger game events, modify Component properties over time and respond to user input in any way you like. More info
See in Glossary required to allow existing assets packed with 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 Packer to continue working after its deprecation from Unity 2020.1 onwards with the following constraints:

1. The Packing Tags property in the Texture Importer settings is set to read-only.
2. Unity will not automatically pack Atlases based on Packing Tags. You will need to call the script provided here, using IPreprocessBuildWithReport.
3. The Sprite Packer Mode setting will only display the Disabled and different Sprite Atlas options. The 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 Legacy option will no longer be available.

Custom Script to force Unity to pack an Atlas for Packing Tags

Use the following script to have Unity pack textures assigned the Packing Tag into an Atlas.

using System.Collections;
using System.Collections.Generic;
using UnityEditor;
using UnityEditor.Build;
using UnityEditor.Build.Reporting;
using UnityEngine;
class BuildPreProcessor : IPreprocessBuildWithReport
{
    public int callbackOrder { get { return 0; } }
    public void OnPreprocessBuild(BuildReport report)
    {
        EditorSettings.spritePackerMode = SpritePackerMode.BuildTimeOnly;
UnityEditor.Sprites.Packer.RebuildAtlasCacheIfNeeded(BuildTarget.StandaloneWindows64, false);
    }
}

Note: The BuildPreProcessor class inherits from IPreprocessBuildWithReport and will only trigger when building.

Conversion script

Use the following conversion script to migrate an existing Packing Tag based Atlas to the 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 system:

using UnityEditor;
using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using UnityEditor.U2D;
using UnityEngine.U2D;
 
public class PrintAtlas : MonoBehaviour
{
    [MenuItem("Atlas/ConvertTags")]
    static void ConvertTags()
    {
        Dictionary<string, List<string>> TagSpriteMap = new Dictionary<string, List<string>>();
 
        foreach (string s in AssetDatabase.GetAllAssetPaths())
        {
            TextureImporter ta = AssetImporter.GetAtPath(s) as TextureImporter;
            if (ta != null)
            {
                if (ta.spritePackingTag != "")
                {
                    if (!TagSpriteMap.ContainsKey(ta.spritePackingTag))
                    {
                        List<string> newList = new List<string>();
                        TagSpriteMap[ta.spritePackingTag] = newList;
                    }
                    TagSpriteMap[ta.spritePackingTag].Add(s);
                }
            }
        }
 
        AssetDatabase.CreateFolder("Assets", "SpriteAtlas");
        foreach (var tagSprite in TagSpriteMap)
        {
            List<string> assetsforTag = tagSprite.Value;
            string alasPath = "Assets/SpriteAtlas/" + tagSprite.Key + ".spriteatlas";
            SpriteAtlas sa = new SpriteAtlas();
            AssetDatabase.CreateAsset(sa, alasPath);
 
            foreach (var asset in assetsforTag)
            {
                Debug.Log(tagSprite.Key + " = " + asset);
                Texture2D tex = AssetDatabase.LoadAssetAtPath<Texture2D>(asset);
                sa.Add(new Object[1] { tex } );
            }
        }
 
        AssetDatabase.SaveAssets();
    }
}

Additional Resources

• Sprite Atlas
• Sprite Atlas V2