It's meant to be simple and easy to use, and therefore it has been made as a custom editor of MeshFilter. It needs no preparations.
Drop the file in an Editor folder.
- store the normals length i editor prefs
- adjust the normals length in the mesh filter inspector
@mandarinx works great! I don't have anough time to fork this, but i think you should add a boolean property like "Show Normals", so you can avoid computations in OnSceneGUI and just return from it. Without it unity starts lagging heavily when large mesh is selected even when you don't need to see normals and set Normal Length to 0.
Or maybe just return from OnSceneGUI when NormalLength == 0.
But i think my option is more logical, so that you don't need to fiddle with normals lenghts just to show it or hide.
Something like this should work