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Writing TINY Desktop Apps in C and GTK3

Jan 15 2022

So you finish up your C/C++ backend, and open up the Electron.js documentation to figure out how to make a quick frontend...

NO!!

You'd better not dare write your desktop application in HTML. What has this world come to???

fat wojak

In this tutorial, I will show you how to write a proper GTK3 app, like a civilized being, instead of shipping your "desktop app" as a website in a web browser.

Setting Up dev stuff

sudo apt install libgtk-3-dev

Yeah, that's it. Assuming you have a C compiler, you're golden.

Now that everything is set up, let's make a real small test file:

#include <gtk/gtk.h>

int main(int argc, char *argv[]) {
    gtk_init(&argc, &argv);

    GtkWidget *window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_window_set_title(GTK_WINDOW(window), "Test Window");
    gtk_window_set_default_size(GTK_WINDOW(window), 300, 300);
    g_signal_connect(window, "delete-event", G_CALLBACK(gtk_main_quit), NULL);
    gtk_widget_show(window);

    GtkWidget *label = gtk_label_new("Hello World");
    gtk_widget_set_hexpand(label, TRUE);
    gtk_label_set_justify(GTK_LABEL(label), GTK_JUSTIFY_CENTER);
    gtk_container_add(GTK_CONTAINER(window), label);
    gtk_widget_show(label);

    gtk_main();
}

And to compile it:

gcc test.c `pkg-config --libs gtk+-3.0 --cflags`

Yay, you've made a decent application!

Of course, you aren't going to write your UI in C, only an idiot would do that. Instead, you want to write it in some kind of markup language. Lucky for us, GTK has just that.

<?xml version="1.0"?>
<interface>
  <object class="GtkApplicationWindow" id="window">
    <child>
      <object class="GtkLabel">
        <property name="label">This is a test</property>
      </object>
    </child>
  </object>
</interface>

And some loader code:

int main(int argc, char *argv[]) {
    gtk_init(&argc, &argv);

    GtkBuilder *builder = gtk_builder_new();
    gtk_builder_add_from_file(builder, "test.ui", NULL)

    GtkWidget *window = GTK_WIDGET(gtk_builder_get_object(builder, "window"));
    g_signal_connect(window, "delete-event", G_CALLBACK(gtk_main_quit), NULL);
    gtk_window_set_title(GTK_WINDOW(window), "Demo Window");
    gtk_window_set_default_size(GTK_WINDOW(window), 300, 100);

    gtk_widget_show_all(window);
    gtk_main();
    return 0;
}

screenshot of window When it comes to loading this binary in, you have a few options: 1. Load a UI file in with linker trickery 2. Convert the file to a C header with xxd -i, and load it in as a string 3. Just load the file in via path

I'm gonna go with xxd.

xxd -i test.ui > test.h

And some loader code:

#include <gtk/gtk.h>
#include "test.h"

static void function(GtkWidget *widget, gpointer data) {
    puts("Hello, World");
}

int main(int argc, char **argv) {
    gtk_init(&argc, &argv);

    GtkBuilder *builder = gtk_builder_new();
    gtk_builder_add_from_string(builder, test_ui, test_ui_len, NULL));

    GtkWidget *window = GTK_WIDGET(gtk_builder_get_object(builder, "window"));
    g_signal_connect(window, "delete-event", G_CALLBACK(gtk_main_quit), NULL);
    gtk_window_set_title(GTK_WINDOW(window), "Demo Window");
    gtk_window_set_default_size(GTK_WINDOW(window), 300, 300);

    GtkWidget *button = GTK_WIDGET(gtk_builder_get_object(builder, "btn"));
    g_signal_connect(button, "clicked", G_CALLBACK(function), NULL);

    gtk_widget_show_all(window);
    gtk_main();
    return 0;
}

The above code creates the same output as the first example.

And now, for my final trick: Easy cross compilation for Windows.

CC=x86_64-w64-mingw32
ZIP=win64-gtk-2021.zip

output: test.exe
    -rm -rf output; mkdir output
    cp win32/lib/* output/
    cp test.exe output/

test.exe: win32
    $(CC)-gcc main.c -Iwin32/include win32/lib/* -o test.exe

win32:
    wget -4 https://github.com/petabyt/windows-gtk/raw/master/$(ZIP)
    unzip *.zip
    rm -rf *.zip

No. That's not a joke. You literally just have to install MinGW (sudo apt install gcc-mingw-w64-x86-64), and you can actually compile this.

Thanks to some archive scouring and msys2 ripping over at my windows-gtk repository, I figured out how to make GTK cross compilation actually not a nightmare.

Here's a simple example you can use to try it out: https://code.theres.life/p/gtk-cross

Good luck, and make sure to have the GTK3 Docs handy at all times.

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