Finally works

This is a good first start to material combining
It may need a few tweaks from here, but for now it should be good

core/packer/rectangle_packer.py

@@ -4,7 +4,7 @@ from __future__ import annotations
 
 
 from typing import Optional
-from bpy.types import Image
+from bpy.types import Image, Material
 
 
 # Copyright (c) 2011, 2012, 2013, 2014, 2015, 2016 Jake Gordon and contributors
@@ -64,7 +64,9 @@ class MaterialImageList:
     emission: Image
     ambient_occlusion: Image
     height: Image
+    roughness: Image
     fit: Rectangle_Obj
+    material: Material
     
     def __init__(self):
         pass

core/properties.py

@@ -70,6 +70,7 @@ def register_properties():
     Material.texture_atlas_emission = EnumProperty(name="Emission", description="The texture that will be used for the emission map atlas", default=0, items=get_texture_node_list)
     Material.texture_atlas_ambient_occlusion = EnumProperty(name="Ambient Occlusion", description="The texture that will be used for the ambient occlusion map atlas", default=0, items=get_texture_node_list)
     Material.texture_atlas_height = EnumProperty(name="Height", description="The texture that will be used for the height map atlas", default=0, items=get_texture_node_list)
+    Material.texture_atlas_roughness = EnumProperty(name="Roughness", description="The texture that will be used for the roughness map atlas", default=0, items=get_texture_node_list)
     
     Scene.texture_atlas_material_index = IntProperty(default=-1, get=(lambda self : -1), set=(lambda self,context : None))