From 422f772c40b490190346b527e0595c450ce1c8a9 Mon Sep 17 00:00:00 2001
From: Andrej730 <azhilenkov@gmail.com>
Date: Wed, 23 Aug 2023 11:07:38 +0500
Subject: [PATCH] Fixed bug with remembering materials assigned to faces

The problem was that bim.update_representation was assigning representation styles without taking into account that some styles may not be actually used in the mesh, so it was always assigning first style (blender material) to the first IFCPOLYGONALFACESET even though it might be using for example the 3rd style.

More - https://community.osarch.org/discussion/1636/materials-not-remembering-their-assigment
---
 .../blenderbim/bim/module/geometry/operator.py       |  2 +-
 src/blenderbim/blenderbim/tool/geometry.py           | 12 ++++++++++--
 2 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/src/blenderbim/blenderbim/bim/module/geometry/operator.py b/src/blenderbim/blenderbim/bim/module/geometry/operator.py
index c4ee14f969..d40edddf47 100644
--- a/src/blenderbim/blenderbim/bim/module/geometry/operator.py
+++ b/src/blenderbim/blenderbim/bim/module/geometry/operator.py
@@ -329,7 +329,7 @@ class UpdateRepresentation(bpy.types.Operator, Operator):
                 "style.assign_representation_styles",
                 self.file,
                 shape_representation=new_representation,
-                styles=tool.Geometry.get_styles(obj),
+                styles=tool.Geometry.get_styles(obj, only_assigned_to_faces=True),
                 should_use_presentation_style_assignment=context.scene.BIMGeometryProperties.should_use_presentation_style_assignment,
             )
             tool.Geometry.record_object_materials(obj)
diff --git a/src/blenderbim/blenderbim/tool/geometry.py b/src/blenderbim/blenderbim/tool/geometry.py
index fe57aa6a76..dbe96048c0 100644
--- a/src/blenderbim/blenderbim/tool/geometry.py
+++ b/src/blenderbim/blenderbim/tool/geometry.py
@@ -396,8 +396,16 @@ class Geometry(blenderbim.core.tool.Geometry):
         return f"{representation.ContextOfItems.id()}/{representation.id()}"
 
     @classmethod
-    def get_styles(cls, obj):
-        return [tool.Style.get_style(s.material) for s in obj.material_slots if s.material]
+    def get_styles(cls, obj, only_assigned_to_faces=False):
+        styles = [tool.Style.get_style(s.material) for s in obj.material_slots if s.material]
+        if not only_assigned_to_faces:
+            return styles
+
+        usage_count = [0] * len(obj.material_slots)
+        for poly in obj.data.polygons:
+            usage_count[poly.material_index] += 1
+        styles = [style for style, usage in zip(styles, usage_count, strict=True) if usage > 0]
+        return styles
 
     # TODO: multiple Literals?
     @classmethod