GeometryProtocol

public protocol GeometryProtocol

The GeometryProtocol protocol exposes the methods and properties of an underlying GdkGeometry instance. The default implementation of these can be found in the protocol extension below. For a concrete class that implements these methods and properties, see Geometry. Alternatively, use GeometryRef as a lighweight, unowned reference if you already have an instance you just want to use.

The GdkGeometry struct gives the window manager information about a window’s geometry constraints. Normally you would set these on the GTK+ level using gtk_window_set_geometry_hints(). GtkWindow then sets the hints on the GdkWindow it creates.

gdk_window_set_geometry_hints() expects the hints to be fully valid already and simply passes them to the window manager; in contrast, gtk_window_set_geometry_hints() performs some interpretation. For example, GtkWindow will apply the hints to the geometry widget instead of the toplevel window, if you set a geometry widget. Also, the min_width/min_height/max_width/max_height fields may be set to -1, and GtkWindow will substitute the size request of the window or geometry widget. If the minimum size hint is not provided, GtkWindow will use its requisition as the minimum size. If the minimum size is provided and a geometry widget is set, GtkWindow will take the minimum size as the minimum size of the geometry widget rather than the entire window. The base size is treated similarly.

The canonical use-case for gtk_window_set_geometry_hints() is to get a terminal widget to resize properly. Here, the terminal text area should be the geometry widget; GtkWindow will then automatically set the base size to the size of other widgets in the terminal window, such as the menubar and scrollbar. Then, the width_inc and height_inc fields should be set to the size of one character in the terminal. Finally, the base size should be set to the size of one character. The net effect is that the minimum size of the terminal will have a 1x1 character terminal area, and only terminal sizes on the “character grid” will be allowed.

Here’s an example of how the terminal example would be implemented, assuming a terminal area widget called “terminal” and a toplevel window “toplevel”:

(C Language Example):

    GdkGeometry hints;

    hints.base_width = terminal->char_width;
        hints.base_height = terminal->char_height;
        hints.min_width = terminal->char_width;
        hints.min_height = terminal->char_height;
        hints.width_inc = terminal->char_width;
        hints.height_inc = terminal->char_height;

 gtk_window_set_geometry_hints (GTK_WINDOW (toplevel),
                                GTK_WIDGET (terminal),
                                &hints,
                                GDK_HINT_RESIZE_INC |
                                GDK_HINT_MIN_SIZE |
                                GDK_HINT_BASE_SIZE);

The other useful fields are the min_aspect and max_aspect fields; these contain a width/height ratio as a floating point number. If a geometry widget is set, the aspect applies to the geometry widget rather than the entire window. The most common use of these hints is probably to set min_aspect and max_aspect to the same value, thus forcing the window to keep a constant aspect ratio.