See #1227. Experimental support for 3D layerset slicing.

src/bonsai/bonsai/bim/import_ifc.py

@@ -69,6 +69,9 @@ class MaterialCreator:
         if isinstance(mesh, bpy.types.Curve):
             return
 
+        if mesh.get("has_layer_styles", None) == True:
+            return
+
         self.mesh = mesh
         self.obj = obj
         if element.is_a("IfcTypeProduct"):
@@ -1059,12 +1062,13 @@ class IfcImporter:
             else:
                 mesh["has_cartesian_point_offset"] = False
 
-            return tool.Loader.convert_geometry_to_mesh(
+            mesh = tool.Loader.convert_geometry_to_mesh(
                 geometry,
                 mesh,
                 verts=verts,
                 load_indexed_maps=self.ifc_import_settings.load_indexed_maps,
             )
+            return tool.Loader.slice_layerset_mesh(element, mesh)
         except:
             self.ifc_import_settings.logger.error("Could not create mesh for %s", element)
             import traceback

src/bonsai/bonsai/tool/loader.py

@@ -1018,6 +1018,74 @@ class Loader(bonsai.core.tool.Loader):
         mesh["ios_material_ids"] = ifcopenshell.util.shape.get_faces_material_style_ids(geometry).tolist()
         return mesh
 
+    @classmethod
+    def slice_layerset_mesh(cls, element: ifcopenshell.entity_instance, mesh: bpy.types.Mesh) -> bpy.types.Mesh:
+        if True:  # This feature is still experimental
+            return mesh
+        if not (material := ifcopenshell.util.element.get_material(element)):
+            return mesh
+        elif material.is_a("IfcMaterialLayerSetUsage"):
+            usage = material
+            layer_set = material.ForLayerSet
+            offset = usage.OffsetFromReferenceLine * cls.unit_scale
+            sense_factor = 1 if usage.DirectionSense == "POSITIVE" else -1
+        elif material.is_a("IfcMaterialLayerSet"):
+            usage = None
+            layer_set = material
+            offset = 0
+            sense_factor = 1
+        else:
+            return mesh
+        if len(layer_set.MaterialLayers) == 1:
+            return mesh
+        bm = bmesh.new()
+        bm.from_mesh(mesh)
+        prev_co = None
+        co = Vector((0.0, offset, 0.0))
+        no = Vector((0.0, 1.0, 0.0))
+        # Cache this
+        body = ifcopenshell.util.representation.get_context(tool.Ifc.get(), "Model", "Body", "MODEL_VIEW")
+        styles = {}
+        has_layer_styles = False
+        for i, material in mesh.materials:
+            if style := tool.Ifc.get_entity(material):
+                styles[style] = i
+        for layer in layer_set.MaterialLayers[:-1]:
+            prev_co = co.copy()
+            co.y = layer.LayerThickness * cls.unit_scale * sense_factor
+            bisect_geom = bmesh.ops.bisect_plane(
+                bm, geom=bm.verts[:] + bm.edges[:] + bm.faces[:], dist=0.0001, plane_co=co, plane_no=no
+            )
+            bmesh.ops.duplicate(bm, geom=bisect_geom["geom_cut"])
+            if style := ifcopenshell.util.representation.get_material_style(layer.Material, body):
+                if (material_index := styles.get(style, None)) is None:
+                    material_index = len(mesh.materials)
+                    mesh.materials.append(tool.Ifc.get_object(style))
+                for face in bisect_geom["geom"]:
+                    if isinstance(face, bmesh.types.BMFace):
+                        center = face.calc_center_bounds() * sense_factor
+                        if center.y < co.y and center.y > prev_co.y:
+                            face.material_index = material_index
+                            has_layer_styles = True
+
+        # Last layer
+        layer = layer_set.MaterialLayers[-1]
+        if style := ifcopenshell.util.representation.get_material_style(layer.Material, body):
+            if (material_index := styles.get(style, None)) is None:
+                material_index = len(mesh.materials)
+                mesh.materials.append(tool.Ifc.get_object(style))
+            for face in bisect_geom["geom"]:
+                if isinstance(face, bmesh.types.BMFace):
+                    center = face.calc_center_bounds() * sense_factor
+                    if center.y > co.y:
+                        face.material_index = material_index
+                        has_layer_styles = True
+
+        bm.to_mesh(mesh)
+        bm.free()
+        mesh["has_layer_styles"] = has_layer_styles
+        return mesh
+
     @classmethod
     def create_mesh_from_shape(
         cls,