Mesh Join Bugfix (#4019)

utils/mesh_functions.py

@@ -84,6 +84,13 @@ def apply_matrices(meshes: Iterator[Mesh], matrices: Iterator[List[Matrix]], *,
 
         yield from join_meshes(meshes_py(sub_vertices, sub_edges, sub_polygons))
 
+def has_element(pol_edge):
+    if pol_edge is None:
+        return False
+    if len(pol_edge) > 0 and len(pol_edge[0]) > 0:
+        return True
+    return False
+
 
 @pass_mesh_type
 def join_meshes(meshes: Iterator[PyMesh], *, _mesh_type) -> Iterator[PyMesh]:
@@ -92,10 +99,16 @@ def join_meshes(meshes: Iterator[PyMesh], *, _mesh_type) -> Iterator[PyMesh]:
     joined_polygons = []
     vertexes_number = 0
     for vertices, edges, polygons in meshes:
-        if edges:
-            joined_edges.extend([(e[0] + vertexes_number, e[1] + vertexes_number) for e in edges])
-        if polygons:
-            joined_polygons.extend([[i + vertexes_number for i in p] for p in polygons])
+        if has_element(edges):
+            if isinstance(edges, np.ndarray):
+                joined_edges.extend((edges + vertexes_number).tolist())
+            else:
+                joined_edges.extend([(e[0] + vertexes_number, e[1] + vertexes_number) for e in edges])
+        if has_element(polygons):
+            if isinstance(edges, np.ndarray):
+                joined_polygons.extend((polygons + vertexes_number).tolist())
+            else:
+                joined_polygons.extend([[i + vertexes_number for i in p] for p in polygons])
         vertexes_number += len(vertices)
         _vertices.append(vertices)
     implementation = np.concatenate if _mesh_type == 'NP' else lambda vs: [v for _vs in vs for v in _vs]