graphics/: Windows can now be created in the hidden state. This can be used to clean up initial window presentation which may involve several steps. This makes those steps all invisible until nx[tk]_setvisibility() is called to make the windows visible.

libs/libnx/nxtk/nxtk_openwindow.c

@@ -89,9 +89,11 @@ nxgl_mxpixel_t g_bordercolor3[CONFIG_NX_NPLANES] =
  *
  * Input Parameters:
  *   handle - The handle returned by nx_connect
- *   flags  - Optional flags.  Must be zero unless CONFIG_NX_RAMBACKED is
- *            enabled.  In that case, it may be zero or
- *            NXBE_WINDOW_RAMBACKED
+ *   flags  - Optional flags.  These include:
+ *            NXBE_WINDOW_RAMBACKED:  Creates a RAM backed window.  This
+ *              option is only valid if CONFIG_NX_RAMBACKED is enabled.
+ *            NXBE_WINDOW_HIDDEN:  The window is create in the HIDDEN state
+ *             and can be made visible later with nxtk_setvisibility().
  *   cb     - Callbacks used to process window events
  *   arg    - User provided value that will be returned with NXTK callbacks.
  *