From 2386ff1abc1f533b88e8886c6b986321a0d561a3 Mon Sep 17 00:00:00 2001
From: Roy-043 <70520633+Roy-043@users.noreply.github.com>
Date: Mon, 20 Oct 2025 15:44:37 +0200
Subject: [PATCH] BIM: fix multi-material transparency IFC export issue
 (#24643)

* BIM: fix multi-material transparency IFC export issue

Fixes #22896.
---
 src/Mod/BIM/importers/exportIFC.py | 32 +++++++++++-------------------
 1 file changed, 12 insertions(+), 20 deletions(-)

diff --git a/src/Mod/BIM/importers/exportIFC.py b/src/Mod/BIM/importers/exportIFC.py
index 89be0fcad2..b50f1db81c 100644
--- a/src/Mod/BIM/importers/exportIFC.py
+++ b/src/Mod/BIM/importers/exportIFC.py
@@ -2517,29 +2517,21 @@ def getRepresentation(
                         rgbt.append(diffusecolor[0])
                     i += len(sol.Faces)
             for i, shape in enumerate(colorshapes):
-                if i < len(rgbt):
-                    key = rgbt[i]
-                else:
-                    key = rgbt[0]
-                # if hasattr(obj,"Material"):
-                #    if obj.Material:
-                #        key = obj.Material.Name #TODO handle multimaterials
+                # TODO handle multimaterials
+                if i >= len(rgbt):
+                    i = 0
+                key = rgbt[i]
+                mat = None
+                if getattr(obj, "Material", None):
+                    mat = obj.Material.Label
+                    if hasattr(obj.Material, "Transparency"):
+                        # Can obj.Material.Transparency (single material) really
+                        # be different from obj.ViewObject.Transparency?
+                        key = key[:3] + (obj.Material.Transparency / 100.0,)
                 if key in surfstyles:
                     psa = surfstyles[key]
                 else:
-                    m = None
-                    if hasattr(obj, "Material"):
-                        if obj.Material:
-                            m = obj.Material.Label
-                            rgbt[i] = (
-                                rgbt[i][0],
-                                rgbt[i][1],
-                                rgbt[i][2],
-                                obj.Material.Transparency / 100.0,
-                            )
-                    psa = ifcbin.createIfcPresentationStyleAssignment(
-                        m, rgbt[i][0], rgbt[i][1], rgbt[i][2], rgbt[i][3]
-                    )
+                    psa = ifcbin.createIfcPresentationStyleAssignment(mat, *key)
                     surfstyles[key] = psa
                 isi = ifcfile.createIfcStyledItem(shape, [psa], None)