Show display sizes and DPI using various GTK+ functions

gtkdpi.cpp

// Compile using the following command
//
//     g++ -Wall -Wno-deprecated-declarations gtkdpi.cpp `pkg-config --cflags --libs gtk+-3.0`
//
// And then run ./a.out
#include <gtk/gtk.h>

static void
print_sizes_and_dpi(int w, int h, int wmm, int hmm)
{
    printf(": %d*%d (%d*%dmm) => %.2f*%.2f DPI\n",
           w, h, wmm, hmm, 25.4*w/wmm, 25.4*h/hmm);
}

static void
activate (GtkApplication* app,
          gpointer        user_data)
{
    GdkScreen* const s = gdk_screen_get_default();
    printf("gdk_screen_get_{width,height}");
    print_sizes_and_dpi(gdk_screen_get_width(s), gdk_screen_get_height(s),
                        gdk_screen_get_width_mm(s), gdk_screen_get_height_mm(s));

    GdkRectangle r;

    const gint n = gdk_screen_get_n_monitors(s);
    for (int i = 0; i < n; ++i) {
        gdk_screen_get_monitor_geometry(s, i, &r);

        printf("gdk_screen_get_monitor(%d)", i);
        print_sizes_and_dpi(r.width, r.height,
                            gdk_screen_get_monitor_width_mm(s, i),
                            gdk_screen_get_monitor_height_mm(s, i));
    }

    GdkDisplay* const d = gdk_display_get_default();
    GdkMonitor* const m = gdk_display_get_primary_monitor(d);

    gdk_monitor_get_geometry(m, &r);
    printf("gdk_monitor_get_geometry");
    print_sizes_and_dpi(r.width, r.height,
                        gdk_monitor_get_width_mm(m),
                        gdk_monitor_get_height_mm(m));
}

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

  app = gtk_application_new ("org.gtk.example", G_APPLICATION_FLAGS_NONE);
  g_signal_connect (app, "activate", G_CALLBACK (activate), NULL);
  status = g_application_run (G_APPLICATION (app), argc, argv);
  g_object_unref (app);

  return status;
}