Evas GL: Doc: Tell people not to read info from Evas_Native_Surface

The information set there is not meant to be read by applications
and reused there. This would break the whole concept of letting
Evas deal with its surfaces.

Ideally Evas GL should not expose texture or fbo ID to external
applications. We could even use a new (non public) surface type
for that purpose.

src/lib/evas/Evas_Common.h

@@ -491,6 +491,12 @@ typedef enum _Evas_Native_Surface_Type
  * @warning Native surface types totally depend on the system. Please
  *          be aware that the types are supported on your system before using
  *          them.
+ *
+ * @note The information stored in an @c Evas_Native_Surface returned by
+ *       @ref evas_gl_native_surface_get() is not meant to be used by
+ *       applications except for passing it to
+ *       @ref evas_object_image_native_surface_set().
+ *
  * @see evas_object_image_native_surface_set()
  */
 struct _Evas_Native_Surface

src/lib/evas/Evas_GL.h

@@ -681,6 +681,10 @@ EAPI Evas_GL_Func             evas_gl_proc_address_get   (Evas_GL *evas_gl, cons
  * @details This function can be called to later set this native surface as
  *          source of an Evas Object Image. Please refer to
  *          @ref evas_object_image_native_surface_set.
+ *
+ * @warning Applications should not rely on the information set in @p ns
+ *          since its properties are internal to Evas and are not meant to be
+ *          tampered with in any way or form from outside Evas.
  */
 EAPI Eina_Bool                evas_gl_native_surface_get (Evas_GL *evas_gl, Evas_GL_Surface *surf, Evas_Native_Surface *ns) EINA_ARG_NONNULL(1,2,3);