Atlas Generator Package

Packages/com.happyrobot33.atlasgenerator/Editor/Atlas Generator.asmdef

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+{
+    "name": "com.happyrobot33.editorgames.atlasgenerator",
+    "rootNamespace": "",
+    "references": [],
+    "includePlatforms": [
+        "Editor"
+    ],
+    "excludePlatforms": [],
+    "allowUnsafeCode": false,
+    "overrideReferences": false,
+    "precompiledReferences": [],
+    "autoReferenced": true,
+    "defineConstraints": [],
+    "versionDefines": [],
+    "noEngineReferences": false
+}

Packages/com.happyrobot33.atlasgenerator/Editor/AtlasGenerator.cs

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+using System.Collections;
+using System.Collections.Generic;
+using UnityEngine;
+using UnityEditor;
+
+namespace HappysTools.AtlasGenerator
+{
+    class AtlasGenerator : AssetPostprocessor
+    {
+        static void OnPostprocessAllAssets(string[] importedAssets, string[] deletedAssets, string[] movedAssets, string[] movedFromAssetPaths, bool didDomainReload)
+        {
+            //gather up all changed textures
+            List<Texture2D> changedTextures = new List<Texture2D>();
+            foreach (string assetPath in importedAssets)
+            {
+                //load the asset
+                Object asset = AssetDatabase.LoadAssetAtPath<Object>(assetPath);
+
+                //check if the asset is a texture
+                if (asset is Texture2D)
+                {
+                    //add the texture to the list
+                    changedTextures.Add((Texture2D)asset);
+                }
+            }
+
+            //if none, return
+            if (changedTextures.Count == 0)
+            {
+                return;
+            }
+
+            List<AtlasInformation> atlasInformationList = AtlasInformation.GetAllAssociatedAtlas(changedTextures.ToArray());
+            //rebuild them
+            foreach (AtlasInformation atlasInformation in atlasInformationList)
+            {
+                atlasInformation.Rebuild();
+            }
+        }
+    }
+}