Bonsai: split multi-material profile sets into per-item shape aspects

DumbProfileGenerator only ever used IfcMaterialProfileSet.CompositeProfile,
or otherwise the first IfcMaterialProfile, when instantiating an occurrence
from a profile-based type, silently discarding every other material profile
in the set (e.g. a steel beam with a timber cladding profile would only
render the steel part, with no way to recover the cladding).

When there is no composite profile but more than one material profile, the
occurrence's Body representation is now built with one extruded item per
IfcMaterialProfile, all sharing a single placement so profiles authored with
a relative offset (e.g. a cladding profile nested against a structural one)
stay correctly positioned. Each item is tagged with an IfcShapeAspect named
after its material profile and gets that material's style applied directly,
mirroring the item/shape-aspect pattern already used by the door and window
representation generators. The element's material assignment keeps
referencing the type's IfcMaterialProfileSetUsage unchanged, since that
already carries the per-profile material; the shape aspect only correlates
each geometry item back to it.

The composite-profile case (an authored single silhouette, e.g. for
structural analysis) is untouched and still takes priority when present.

Fixes #2052.

Generated with the assistance of an AI coding tool.

src/bonsai/bonsai/bim/module/model/profile.py

@@ -24,6 +24,7 @@ import bpy
 import ifcopenshell
 import ifcopenshell.api.geometry
 import ifcopenshell.api.pset
+import ifcopenshell.api.style
 import ifcopenshell.api.type
 import ifcopenshell.util.element
 import ifcopenshell.util.placement
@@ -156,13 +157,25 @@ class DumbProfileGenerator:
                 tool.Ifc.get(), product=element, representation=representation
             )
 
-        representation = ifcopenshell.api.geometry.add_profile_representation(
-            tool.Ifc.get(),
-            context=self.body_context,
-            profile=self.profile_set.CompositeProfile or self.profile_set.MaterialProfiles[0].Profile,
-            cardinal_point=self.cardinal_point,
-            depth=self.depth,
-        )
+        material_profiles = list(self.profile_set.MaterialProfiles or [])
+        # A composite profile is an explicit, authored silhouette (e.g. for structural
+        # analysis) and always takes priority when present, matching prior behaviour.
+        # Only when there's no composite profile AND more than one material profile do
+        # we split the occurrence into one item per material profile, so each keeps its
+        # own material instead of collapsing to the first one.
+        is_multi_material = not self.profile_set.CompositeProfile and len(material_profiles) > 1
+
+        if is_multi_material:
+            representation, items = self.create_multi_material_profile_items(material_profiles)
+        else:
+            representation = ifcopenshell.api.geometry.add_profile_representation(
+                tool.Ifc.get(),
+                context=self.body_context,
+                profile=self.profile_set.CompositeProfile or self.profile_set.MaterialProfiles[0].Profile,
+                cardinal_point=self.cardinal_point,
+                depth=self.depth,
+            )
+
         ifcopenshell.api.geometry.assign_representation(tool.Ifc.get(), product=element, representation=representation)
         bonsai.core.geometry.switch_representation(
             tool.Ifc,
@@ -171,6 +184,9 @@ class DumbProfileGenerator:
             representation=representation,
         )
 
+        if is_multi_material:
+            self.tag_material_profile_items(element, representation, items, material_profiles)
+
         pset = ifcopenshell.api.pset.add_pset(self.file, product=element, name="EPset_Parametric")
         ifcopenshell.api.pset.edit_pset(self.file, pset=pset, properties={"Engine": "Bonsai.DumbProfile"})
 
@@ -178,6 +194,73 @@ class DumbProfileGenerator:
 
         return obj
 
+    def create_multi_material_profile_items(
+        self, material_profiles: list[ifcopenshell.entity_instance]
+    ) -> tuple[ifcopenshell.entity_instance, list[ifcopenshell.entity_instance]]:
+        """Builds a single Body representation with one extruded item per `IfcMaterialProfile`.
+
+        All items share the same placement (derived from the first material profile's
+        cardinal point / bounding box), mirroring how door/window representations combine
+        multiple items in a single coordinate frame: each `IfcProfileDef` in a material
+        profile set is expected to already be positioned relative to that shared origin
+        (e.g. a cladding profile authored with its own offset `Position`), so reusing one
+        placement for every item preserves the intended nesting between profiles.
+        """
+        file = tool.Ifc.get()
+        reference_representation = ifcopenshell.api.geometry.add_profile_representation(
+            file,
+            context=self.body_context,
+            profile=material_profiles[0].Profile,
+            cardinal_point=self.cardinal_point,
+            depth=self.depth,
+        )
+        reference_item = reference_representation.Items[0]
+        items = [reference_item]
+        for material_profile in material_profiles[1:]:
+            items.append(
+                file.create_entity(
+                    "IfcExtrudedAreaSolid",
+                    material_profile.Profile,
+                    reference_item.Position,
+                    reference_item.ExtrudedDirection,
+                    reference_item.Depth,
+                )
+            )
+        reference_representation.Items = items
+        return reference_representation, items
+
+    def tag_material_profile_items(
+        self,
+        element: ifcopenshell.entity_instance,
+        representation: ifcopenshell.entity_instance,
+        items: list[ifcopenshell.entity_instance],
+        material_profiles: list[ifcopenshell.entity_instance],
+    ) -> None:
+        """Tags each item with an `IfcShapeAspect` named after its `IfcMaterialProfile`,
+        and applies that material's style (if any) directly to the item, following the
+        same item-level tagging pattern used by the door/window representation generators.
+
+        The element's own material assignment is left untouched (it keeps referencing the
+        type's `IfcMaterialProfileSetUsage`), since that's what carries the per-profile
+        material information; the shape aspect only correlates geometry items back to it.
+        """
+        file = tool.Ifc.get()
+        part_of_product = ifcopenshell.util.representation.get_part_of_product(element, self.body_context)
+        if not part_of_product:
+            return
+        for index, (item, material_profile) in enumerate(zip(items, material_profiles)):
+            material = material_profile.Material
+            aspect_name = material_profile.Name or (material and material.Name) or f"Profile {index + 1}"
+            ifcopenshell.api.geometry.add_shape_aspect(
+                file,
+                aspect_name,
+                items=[item],
+                representation=representation,
+                part_of_product=part_of_product,
+            )
+            if material and (style := ifcopenshell.util.representation.get_material_style(material, self.body_context)):
+                ifcopenshell.api.style.assign_item_style(file, item=item, style=style)
+
     def create_profile_from_2_points(
         self, coords: tuple[Vector, Vector], should_round: bool = False
     ) -> ProfileFrom2PointsReturn: