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

@@ -1903,16 +1903,18 @@ class CutDecorator:
         # 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
-        last_i = len(layer_set.MaterialLayers) - 1
+            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

@@ -734,10 +734,12 @@ class CreateDrawing(bpy.types.Operator):
             # 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
-            last_i = len(layer_set.MaterialLayers) - 1
-            for i, layer in enumerate(layer_set.MaterialLayers):
+                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/tool/loader.py

@@ -1093,10 +1093,12 @@ class Loader(bonsai.core.tool.Loader):
         # 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 = {}
@@ -1104,8 +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