Ubuntu – How do I use the GtkFontDialog in gtk4?

Gtk4 has the claim to work object-oriented and with lists.
Accordingly, the fonts of GtkFontDialog are represented as GtkFilterListModel. So if you only want to show one selection, you need a GtkFilter. Since GtkFilter is an abstract class, you have to derive your own and implement the filter criteria there. For this purpose, the function ‘match’ is overwritten, which iterated with the parameter "item" over all fonds passed by GtkFontDialog.
"item" is passed as PangoFondFace.A return value of TRUE means: the fond is displayed. FALSE, it will not be displayed.

A simple variant can look like this:

class-font-filter.h

 
#pragma once
#include<gtk/gtk.h>

#define  FONT_TYPE_FILTER (font_filter_get_type())
 
G_DECLARE_FINAL_TYPE (FontFilter, font_filter,  FONT, FILTER, GtkFilter)
 
GtkFilter *font_filter_new();

class-font-filter.c

#include"class-font-filter.h"

struct _FontFilter
{
  GtkFilter parent_instance;
};
 
struct _FontFilterClass
{
  GtkFilterClass parent_class;
};
 
G_DEFINE_TYPE (FontFilter, font_filter, GTK_TYPE_FILTER)
 
static void
font_filter_init(FontFilter *self)
{
}
 
gboolean font_filter_match (GtkFilter *self, gpointer item )
{
    PangoFontFace * face =(PANGO_FONT_FACE(item));
    const char *font_name = pango_font_face_get_face_name(face);
    PangoFontFamily *family = pango_font_face_get_family(face);
    const char *family_name = pango_font_family_get_name(family);

    if (strcmp(family_name, "Ubuntu") == 0 && strcmp(font_name, "Regular") == 0 )
             return TRUE; 
    else  if (strcmp(family_name, "FreeMono") == 0 && strcmp(font_name, "Regular") == 0 )
        return TRUE;
    else if (strcmp(family_name, "Mitra") == 0)
         return TRUE;
     else
             return FALSE;

}



static void
font_filter_class_init (FontFilterClass *class)
{
        GTK_FILTER_CLASS(class)->match = font_filter_match;
}
 
GtkFilter *
font_filter_new ()
{
FontFilter *self;
 
  self = g_object_new (FONT_TYPE_FILTER,NULL);

  return GTK_FILTER (self);
 }

This is then integrated into the program:

font-dialog.h

#include<gtk/gtk.h>

void activate(GtkApplication *app, gpointer data);

font-dialog.c

 
#include"font-dialog.h"
#include"class-font-filter.h"

void chow_font(GtkWidget *f_button)
{
 PangoFontDescription* fontdescription = gtk_font_dialog_button_get_font_desc (GTK_FONT_DIALOG_BUTTON(f_button));

 char* font = pango_font_description_to_string (fontdescription); 
 
 g_print ("The selectet fond is:  %sn",font); 

}

void activate (GtkApplication *app, gpointer data)
{
  GtkWidget *window;

  window =gtk_application_window_new(app);
  gtk_widget_set_size_request(window,50,50);
 
  GtkFontDialog* fontdialog = gtk_font_dialog_new ();

  GtkWidget* f_button = gtk_font_dialog_button_new (fontdialog);

  g_signal_connect(f_button,"notify::font-desc", G_CALLBACK(chow_font),NULL);
 
  GtkFilter* filter = font_filter_new();

  gtk_font_dialog_set_filter ( fontdialog, GTK_FILTER(filter));

  gtk_window_set_child(GTK_WINDOW(window),f_button);
 
 gtk_widget_set_visible(window,TRUE);
}

And the completeness sake:

main-font-dialog.c

#include"font-dialog.h"

int
main (int argc, char **argv)
{
  GtkApplication *app;
  int status;

  app = gtk_application_new ("holger.gtk.font-dialog", G_APPLICATION_DEFAULT_FLAGS);
  g_signal_connect (app, "activate", G_CALLBACK (activate), NULL);
  status = g_application_run (G_APPLICATION (app), argc, argv);
  g_object_unref (app);

  return status;
}

If you want to make it a little more elaborate, you can also put the fonts to be selected in a list, which is then given when the class FontFilter is initiated.Of course, then, the function font-filter-match(…)
be adjusted accordingly.

But the principle should have become clear.

Alternatively, there is also the possibility to write an own PangoFontMap class, which can then also be derived from the corresponding abstract class. Their object instance can then be used with gtk-font-dialog-set-font-map() to be made available to the GtkFond dialog.

Have fun experimenting.