10.4. Layout Container

The Layout container is similar to the Fixed container except that it implements an infinite (where infinity is less than 2^32) scrolling area. The X window system has a limitation where windows can be at most 32767 pixels wide or tall. The Layout container gets around this limitation by doing some exotic stuff using window and bit gravities, so that you can have smooth scrolling even when you have many child widgets in your scrolling area.

A Layout container is created using:

GtkWidget *gtk_layout_new( GtkAdjustment *hadjustment,
                           GtkAdjustment *vadjustment );

As you can see, you can optionally specify the Adjustment objects that the Layout widget will use for its scrolling.

You can add and move widgets in the Layout container using the following two functions:

void gtk_layout_put( GtkLayout *layout,
                     GtkWidget *widget,
                     gint       x,
                     gint       y );

void gtk_layout_move( GtkLayout *layout,
                      GtkWidget *widget,
                      gint       x,
                      gint       y );

The size of the Layout container can be set using the next function:

void gtk_layout_set_size( GtkLayout *layout,
                          guint      width,
                          guint      height );

Layout containers are one of the very few widgets in the GTK widget set that actively repaint themselves on screen as they are changed using the above functions (the vast majority of widgets queue requests which are then processed when control returns to the gtk_main() function).

When you want to make a large number of changes to a Layout container, you can use the following two functions to disable and re-enable this repainting functionality:

void gtk_layout_freeze( GtkLayout *layout );

void gtk_layout_thaw( GtkLayout *layout );

The final four functions for use with Layout widgets are for manipulating the horizontal and vertical adjustment widgets:

GtkAdjustment* gtk_layout_get_hadjustment( GtkLayout *layout );

GtkAdjustment* gtk_layout_get_vadjustment( GtkLayout *layout );

void gtk_layout_set_hadjustment( GtkLayout     *layout,
                                 GtkAdjustment *adjustment );

void gtk_layout_set_vadjustment( GtkLayout     *layout,
                                 GtkAdjustment *adjustment);