This extension defines an UI type for the in-process UI extension that can be used in a Gtk+ program.
The class which represents a Gtk+ UI. For a successfully created instance of an UI of this class, the get_widget() function MUST return a pointer to a valid GtkWidget object compatible with Gtk+ version 2.0. The host MUST ensure that the Gtk+ library has been initialised and that the Glib main loop is running before an UI of this type is instantiated. Unless otherwise specified by extensions, all function pointers in LV2_UI_Descriptor may only be called from the thread that runs the Glib main loop.
This Feature should only be used with UIs. When this Feature is active the host SHOULD NOT resize the UI widget to any other size than the one given by gtk_widget_size_request(). However, the UI MUST NOT break if the widget is resized to another size. This Feature can be used for example when the widget uses a fixed-size pixmap interface. The data pointer in the LV2_Feature object for this Feature should be set to NULL.