fix [#31598] Messed up Smart UVs

face areas were too close to zero. also copy the face normal to avoid recalculations on each use.

release/scripts/startup/bl_operators/uvcalc_smart_project.py

@@ -23,7 +23,7 @@ import bpy
 from bpy.types import Operator
 
 DEG_TO_RAD = 0.017453292519943295 # pi/180.0
-SMALL_NUM = 0.000000001
+SMALL_NUM = 0.0000001  # see bug [#31598] why we dont have smaller values
 BIG_NUM = 1e15
 
 global USER_FILL_HOLES
@@ -759,7 +759,7 @@ class thickface(object):
         self.v = [mesh_verts[i] for i in face.vertices]
         self.uv = [uv_layer[i].uv for i in face.loop_indices]
 
-        self.no = face.normal
+        self.no = face.normal.copy()
         self.area = face.area
         self.edge_keys = face.edge_keys