[Python Viewer] Allow users to override rendering flags via user_scn.

Fixes #1190

PiperOrigin-RevId: 603672602
Change-Id: I3ff1bb0dca7e913b36f1b241aaea8b8bb95cadff

doc/python.rst

@@ -124,15 +124,21 @@ attributes:
 - ``is_running()``: returns ``True`` if the viewer window is running and ``False`` if it is closed.
   This method can be safely called without locking.
 
-- ``user_scn``: an :ref:`mjvScene` object that allows users to add custom visualization geoms to the rendered scene.
-  This is separate from the ``mjvScene`` that the viewer uses internally to render the final scene, and is entirely
-  under the user's control. User scripts can call e.g. :ref:`mjv_initGeom` or :ref:`mjv_makeConnector` to add
-  visualization geoms to ``user_scn``, and upon the next call to ``sync()``, the viewer will incorporate
-  these geoms to future rendered images. For example:
+- ``user_scn``: an :ref:`mjvScene` object that allows users to add change rendering flags and add custom
+  visualization geoms to the rendered scene. This is separate from the ``mjvScene`` that the viewer uses internally to
+  render the final scene, and is entirely under the user's control. User scripts can call e.g. :ref:`mjv_initGeom` or
+  :ref:`mjv_makeConnector` to add visualization geoms to ``user_scn``, and upon the next call to ``sync()``, the viewer
+  will incorporate these geoms to future rendered images. Similarly, user scripts can make changes to ``user_scn.flags``
+  which would be picked up at the next call to ``sync()``. The ``sync()`` call also copies changes to rendering flags
+  made via the GUI back into ``user_scn`` to preserve consistency. For example:
 
   .. code-block:: python
 
     with mujoco.viewer.launch_passive(m, d, key_callback=key_callback) as viewer:
+
+      # Enable wireframe rendering of the entire scene.
+      v.user_scn.flags[mujoco.mjtRndFlag.mjRND_WIREFRAME] = 1
+
       while viewer.is_running():
         ...
         # Step the physics.