The icon defined in 'gtk_windows_set_default_icon' is not rendered on the Unity launcher. Instead it keeps displaying the icon as defined in the .desktop file.
This is different to the behaviour of e.g. the GNOME panel and other launchers where the windows icon is updated and thus can nicely be used for displaying a program's state or for drawing user's attention to the application if runs iconified.
The icon defined in 'gtk_windows_ set_default_ icon' is not rendered on the Unity launcher. Instead it keeps displaying the icon as defined in the .desktop file.
This is different to the behaviour of e.g. the GNOME panel and other launchers where the windows icon is updated and thus can nicely be used for displaying a program's state or for drawing user's attention to the application if runs iconified.