Fix inverted layer order for flipped slab direction

When the mesh centroid check detects a direction mismatch
and flips `no`, also reverse the layer list so layer ordering
remains consistent with the reference line convention.

Generated with the assistance of an AI coding tool.

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

@@ -1898,14 +1898,23 @@ class CutDecorator:
             no = tool.Drawing.get_extrusion_vector(element).normalized()
             no = Vector([1.0, 0.0, 0.0])
         no *= sense_factor
-        last_i = len(layer_set.MaterialLayers) - 1
+        # Detect non-conformant exports (e.g. Revit) where DirectionSense=POSITIVE
+        # but the geometry extrudes in the negative direction. If the mesh centroid
+        # in object local space is on the wrong side of the starting plane, flip no.
+        bb = [Vector(v) for v in obj.bound_box]
+        mesh_centroid = sum(bb, Vector((0.0, 0.0, 0.0))) / 8
+        layers = list(layer_set.MaterialLayers)
+        if (mesh_centroid - co).dot(no) < 0:
+            no = -no
+            layers = list(reversed(layers))
+        last_i = len(layers) - 1
 
         vert_map = {}
         verts = []
         edges = []
         j = 0
 
-        for i, layer in enumerate(layer_set.MaterialLayers):
+        for i, layer in enumerate(layers):
             prev_co = co.copy()
             co += no * layer.LayerThickness * self.unit_scale
             if i != last_i:

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

@@ -729,8 +729,17 @@ class CreateDrawing(bpy.types.Operator):
                 no = tool.Drawing.get_extrusion_vector(element).normalized()
                 no = Vector([1.0, 0.0, 0.0])
             no *= sense_factor
-            last_i = len(layer_set.MaterialLayers) - 1
-            for i, layer in enumerate(layer_set.MaterialLayers):
+            # Detect non-conformant exports (e.g. Revit) where DirectionSense=POSITIVE
+            # but the geometry extrudes in the negative direction. If the mesh centroid
+            # in object local space is on the wrong side of the starting plane, flip no.
+            bb = [Vector(v) for v in obj.bound_box]
+            mesh_centroid = sum(bb, Vector((0.0, 0.0, 0.0))) / 8
+            layers = list(layer_set.MaterialLayers)
+            if (mesh_centroid - co).dot(no) < 0:
+                no = -no
+                layers = list(reversed(layers))
+            last_i = len(layers) - 1
+            for i, layer in enumerate(layers):
                 prev_co = co.copy()
                 co += no * layer.LayerThickness * self.unit_scale
 

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

@@ -248,7 +248,8 @@ class DumbSlabPlaner:
 
     def change_thickness(self, element: ifcopenshell.entity_instance, thickness: float) -> None:
         self.unit_scale = ifcopenshell.util.unit.calculate_unit_scale(tool.Ifc.get())
-        if tool.Model.get_usage_type(element) != "LAYER3":
+        usage_type = tool.Model.get_usage_type(element)
+        if usage_type != "LAYER3":
             return
         layer_params = tool.Model.get_material_layer_parameters(element)
         ifc_file = tool.Ifc.get()
@@ -304,11 +305,15 @@ class DumbSlabPlaner:
                 ifc_position = extrusion.Position
                 position = offset_direction * perpendicular_offset
                 material = ifcopenshell.util.element.get_material(element)
-                if material:
-                    if material.is_a("IfcMaterialLayerSetUsage"):
-                        material.OffsetFromReferenceLine = position.z
                 if ifc_position:
-                    ifc_position.Location.Coordinates = position
+                    orig = Vector(ifc_position.Location.Coordinates)
+                    layer_normal = offset_direction.normalized()
+                    perp = orig - orig.dot(layer_normal) * layer_normal
+                    new_coords = perp + layer_normal * perpendicular_offset
+                    ifc_position.Location.Coordinates = new_coords
+                    if material:
+                        if material.is_a("IfcMaterialLayerSetUsage"):
+                            material.OffsetFromReferenceLine = new_coords.z
                 else:
                     tool.Model.add_extrusion_position(extrusion, position)
 

src/bonsai/bonsai/tool/loader.py

@@ -1090,6 +1090,15 @@ class Loader(bonsai.core.tool.Loader):
             no = cls.get_extrusion_vector(element).normalized()
             no = Vector([1.0, 0.0, 0.0])
         no *= sense_factor
+        # Detect non-conformant exports (e.g. Revit) where DirectionSense=POSITIVE
+        # but the geometry extrudes in the negative direction. If the mesh centroid
+        # in object local space is on the wrong side of the starting plane, flip no.
+        layers = list(layer_set.MaterialLayers)
+        if bm.verts:
+            mesh_centroid = sum((v.co for v in bm.verts), Vector((0.0, 0.0, 0.0))) / len(bm.verts)
+            if (mesh_centroid - co).dot(no) < 0:
+                no = -no
+                layers = list(reversed(layers))
         # Cache this
         body = ifcopenshell.util.representation.get_context(tool.Ifc.get(), "Model", "Body", "MODEL_VIEW")
         styles = {}
@@ -1097,8 +1106,8 @@ class Loader(bonsai.core.tool.Loader):
         for i, material in enumerate(mesh.materials):
             if style := tool.Ifc.get_entity(material):
                 styles[style] = i
-        last_i = len(layer_set.MaterialLayers) - 1
-        for i, layer in enumerate(layer_set.MaterialLayers):
+        last_i = len(layers) - 1
+        for i, layer in enumerate(layers):
             if i != last_i:
                 prev_co = co.copy()
                 co += no * layer.LayerThickness * cls.unit_scale