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10.6 Aspect Frames

　　The aspect frame widget is like a frame widget, except that it also enforces the aspect ratio (that is, the ratio of the width to the height) of the child widget to have a certain value, adding extra space if necessary. This is useful, for instance, if you want to preview a larger image. The size of the preview should vary when the user resizes the window, but the aspect ratio needs to always match the original image.

　　To create a new aspect frame use:

GtkWidget *gtk_aspect_frame_new( const gchar *label,
gfloat xalign,gfloat yalign,gfloat ratio,gint obey_child);

　　xalign and yalign specify alignment as with Alignment widgets. If obey_child is true, the aspect ratio of a child widget will match the aspect ratio of the ideal size it requests. Otherwise, it is given by ratio.

　　To change the options of an existing aspect frame, you can use:

void gtk_aspect_frame_set( GtkAspectFrame *aspect_frame,
gfloatxalign,gfloatyalign,gfloatratio,gintobey_child);

　　As an example, the following program uses an AspectFrame to present a drawing area whose aspect ratio will always be 2:1, no matter how the user resizes the top-level window.

/* example-start aspectframe aspectframe.c */
#include <gtk/gtk.h>
int main( int argc,
char *argv[] )
{
GtkWidget *window;
GtkWidget *aspect_frame;
GtkWidget *drawing_area;
gtk_init (&argc, &argv);
window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
gtk_window_set_title (GTK_WINDOW (window), "Aspect Frame");
gtk_signal_connect (GTK_OBJECT (window), "destroy",
GTK_SIGNAL_FUNC (gtk_main_quit), NULL);
gtk_container_set_border_width (GTK_CONTAINER (window), 10);
/* Create an aspect_frame and add it to our toplevel window */
aspect_frame = gtk_aspect_frame_new ("2x1", /* label */
 0.5, /* center x */
 0.5, /* center y */
 2, /* xsize/ysize = 2 */
 FALSE /* ignore child's aspect */);
gtk_container_add (GTK_CONTAINER(window), aspect_frame);
gtk_widget_show (aspect_frame);
/* Now add a child widget to the aspect frame */
drawing_area = gtk_drawing_area_new ();
/* Ask for a 200x200 window, but the AspectFrame will give us a 200x100
 * window since we are forcing a 2x1 aspect ratio */
gtk_widget_set_usize (drawing_area, 200, 200);
gtk_container_add (GTK_CONTAINER(aspect_frame), drawing_area);
gtk_widget_show (drawing_area);
gtk_widget_show (window);
gtk_main ();
return 0;
}
/* example-end */

10.7 Paned Window Widgets

　　The paned window widgets are useful when you want to divide an area into two parts, with the relative size of the two parts controlled by the user. A groove is drawn between the two portions with a handle that the user can drag to change the ratio. The division can either be horizontal (HPaned) or vertical (VPaned).

　　To create a new paned window, call one of:

GtkWidget *gtk_hpaned_new (void);
GtkWidget *gtk_vpaned_new (void);

　　After creating the paned window widget, you need to add child widgets to its two halves. To do this, use the functions:

void gtk_paned_add1 (GtkPaned *paned, GtkWidget *child);
void gtk_paned_add2 (GtkPaned *paned, GtkWidget *child);

　　gtk_paned_add1() adds the child widget to the left or top half of the paned window. gtk_paned_add2() adds the child widget to the right or bottom half of the paned window.

　　A paned widget can be changed visually using the following two functions.

void gtk_paned_set_handle_size( GtkPaned *paned,guint16 size);
void gtk_paned_set_gutter_size( GtkPaned *paned,guint16 size);

　　The first of these sets the size of the handle and the second sets the size of the gutter that is between the two parts of the paned window.

　　As an example, we will create part of the user interface of an imaginary email program. A window is divided into two portions vertically, with the top portion being a list of email messages and the bottom portion the text of the email message. Most of the program is pretty straightforward. A couple of points to note: text can't be added to a Text widget until it is realized. This could be done by calling gtk_widget_realize(), but as a demonstration of an alternate technique, we connect a handler to the "realize" signal to add the text. Also, we need to add the GTK_SHRINK option to some of the items in the table containing the text window and its scrollbars, so that when the bottom portion is made smaller, the correct portions shrink instead of being pushed off the bottom of the window.