See #1227. Merging doubles gives more reliable results in bisection fills.

src/bonsai/bonsai/bim/module/drawing/decoration.py

@@ -1724,16 +1724,14 @@ class CutDecorator:
         bm_original.from_mesh(mesh)
 
         if not (material := ifcopenshell.util.element.get_material(element)):
-            geom = bm_original.verts[:] + bm_original.edges[:] + bm_original.faces[:]
-            verts, tris = self.bisect_mesh_tris(obj, bm_original, geom, context.scene.camera)
+            verts, tris = self.bisect_mesh_tris(obj, bm_original, context.scene.camera)
             DecoratorData.fill_cache[element_id].setdefault(self.fallback_colour, []).append((verts, tris))
             return
 
         if material.is_a() not in ("IfcMaterialLayerSet", "IfcMaterialLayerSetUsage"):
             # Constituents, lists, and item styles not supported yet
             material = ifcopenshell.util.element.get_materials(element)[0]
-            geom = bm_original.verts[:] + bm_original.edges[:] + bm_original.faces[:]
-            verts, tris = self.bisect_mesh_tris(obj, bm_original, geom, context.scene.camera)
+            verts, tris = self.bisect_mesh_tris(obj, bm_original, context.scene.camera)
             colour = self.get_material_colour(material)
             DecoratorData.fill_cache[element_id].setdefault(colour, []).append((verts, tris))
             return
@@ -1753,8 +1751,7 @@ class CutDecorator:
 
         if len(layer_set.MaterialLayers) == 1:
             material = layer_set.MaterialLayers[0].Material
-            geom = bm_original.verts[:] + bm_original.edges[:] + bm_original.faces[:]
-            verts, tris = self.bisect_mesh_tris(obj, bm_original, geom, context.scene.camera)
+            verts, tris = self.bisect_mesh_tris(obj, bm_original, context.scene.camera)
             colour = self.get_material_colour(material)
             DecoratorData.fill_cache[element_id].setdefault(colour, []).append((verts, tris))
             return
@@ -1809,8 +1806,7 @@ class CutDecorator:
                 edges = [g for g in bisect["geom_cut"] if isinstance(g, bmesh.types.BMEdge)]
                 fill = bmesh.ops.edgenet_fill(bm_fill, edges=edges)
 
-            geom = bm_fill.verts[:] + bm_fill.edges[:] + bm_fill.faces[:]
-            verts, tris = self.bisect_mesh_tris(obj, bm_fill, geom, context.scene.camera)
+            verts, tris = self.bisect_mesh_tris(obj, bm_fill, context.scene.camera)
             DecoratorData.fill_cache[element_id].setdefault(colour, []).append((verts, tris))
 
         verts, edges = self.bisect_mesh(obj, bm, slice_plane_geom, context.scene.camera)
@@ -1861,18 +1857,19 @@ class CutDecorator:
 
         return verts, edges
 
-    def bisect_mesh_tris(self, obj, bm, geom, camera):
+    def bisect_mesh_tris(self, obj, bm, camera):
         camera_matrix = obj.matrix_world.inverted() @ camera.matrix_world
         plane_co = camera_matrix.translation
         plane_no = camera_matrix.col[2].xyz
 
         global_offset = camera.matrix_world.col[2].xyz * -camera.data.clip_start
 
+        geom = bm.verts[:] + bm.edges[:] + bm.faces[:]
         bmesh.ops.bisect_plane(
             bm, geom=geom, dist=0.0001, plane_co=plane_co, plane_no=plane_no, clear_inner=True, clear_outer=True
         )
-        bmesh.ops.remove_doubles(bm, verts=bm.verts[:])
-        fill = bmesh.ops.edgenet_fill(bm, edges=bm.edges[:])
+        bmesh.ops.remove_doubles(bm, verts=bm.verts, dist=1e-6)
+        fill = bmesh.ops.edgenet_fill(bm, edges=bm.edges)
         triangulate = bmesh.ops.triangulate(bm, faces=fill["faces"])
 
         vert_map = {}

src/bonsai/bonsai/tool/loader.py

@@ -1062,17 +1062,26 @@ class Loader(bonsai.core.tool.Loader):
                 styles[style] = i
         last_i = len(layer_set.MaterialLayers) - 1
         for i, layer in enumerate(layer_set.MaterialLayers):
-            prev_co = co.copy()
-            co += no * layer.LayerThickness * cls.unit_scale
             if i != last_i:
+                prev_co = co.copy()
+                co += no * layer.LayerThickness * cls.unit_scale
                 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))
+            if not (style := ifcopenshell.util.representation.get_material_style(layer.Material, body)):
+                continue
+            if (material_index := styles.get(style, None)) is None:
+                material_index = len(mesh.materials)
+                mesh.materials.append(tool.Ifc.get_object(style))
+            if i == last_i:
+                for face in bisect_geom["geom"]:
+                    if isinstance(face, bmesh.types.BMFace):
+                        center = face.calc_center_median()
+                        if (center - co).dot(no) >= 0:
+                            face.material_index = material_index
+                            has_layer_styles = True
+            else:
                 for face in bisect_geom["geom"]:
                     if isinstance(face, bmesh.types.BMFace):
                         center = face.calc_center_median()