Cross-compile a GTK3 app from Linux to Windows with native Windows look and feel28.02.25

Cross-compile a GTK3 app from Linux to Windows with native Windows look and feel

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August 2020

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One of my research projects involved writing a Windows app for a department at my school, but I only run Linux. I saved the steps for building a GUI GTK3 program on both Linux and Windows. This includes the frills most Windows users expect, like a graphical installer, an icon on the executable, and a program that looks like it was made for Windows.

You can view the results of the tutorial (the resulting source code and files) in this repository.

As a starter program, create the demo C program from the GTK documentation and save it as main.c.

To compile the code on Linux, a simple

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

will do the trick (you need pkg-config, GCC, and GTK3 installed). Test the executable to make sure it works:

./main

Windows setup

To build for Windows, you need to use MinGW to compile the executable, and then you need to bundle the MinGW GTK dlls so they're available at runtime on Windows.

First install MinGW. If this step seems insurmountable, or if you're running Arch Linux or a similar distro, just skip to the Automating builds section.

On Fedora, for example, you can install everything you need with this command:

dnf install mingw64-gtk3 mingw32-binutils mingw32-nsiswrapper

Compiling for Windows

On a Linux system with MinGW installed you can compile the same program with something like:

x86_64-w64-mingw32-gcc -o main main.c `mingw64-pkg-config --cflags gtk+-3.0 --libs gtk+-3.0`

You should now have an executable called main.exe. Obviously this executable won't work on Linux, but it also won't work on Windows until you make the GTK libraries available to it at runtime.
Bundle GTK libraries

Make a subdirectory called windows and copy the .exe into it. Now copy the MinGW libraries over to the same folder. Unfortunately, different Linux distributions have different locations (and sometimes even different names) for the MinGW executables. On Fedora, they're found at /usr/x86_64-w64-mingw32/sys-root/mingw/*.
Test on Windows

If you copy the whole windows folder to a Windows computer or VM, the program should now run as expected. Magically enough, WINE is also able to run the program from Linux.

However, the program looks bad because

it uses GNOME's Adwaita theme (which looks bad on Windows)
    it uses GTK to render the client-side decorations (the top of the window with the exit button)
    there's no icon for the program in Windows' taskbar
    the program runs with a black command prompt window in the background.

Furthermore, it's not ideal to distribute the program by zipping up this folder and sharing it.
Fix Icon

Download or create an icon. From within the code you can set the icon for the program like this:

GdkPixbuf *icon;
icon = create_pixbuf("icon.ico");
gtk_window_set_icon(GTK_WINDOW(window), icon);

The code for create_pixbuf is:

GdkPixbuf *create_pixbuf(const gchar * filename) {

GdkPixbuf *pixbuf;
   GError *error = NULL;
   pixbuf = gdk_pixbuf_new_from_file(filename, &error);

if (!pixbuf) {

fprintf(stderr, "%s\n", error->message);
	  g_error_free(error);
   }

return pixbuf;
}

This will change the icon of the program while it's running. It shows up correctly in the Windows taskbar and window decorations, but it won't change the icon of the actual .exe. I still recommend including this code because it works to set the icon on Linux desktop environments.

To change the icon of the executable file on Windows, we have to use MinGW's windres utility. Create a file called "icon.rc" with the contents:

id ICON "icon.ico"

and then run:

x86_64-w64-mingw32-windres icon.rc -O coff -o icon.res

Now we can add the icon.res resource file to the executable by slightly modifying our GCC command:

x86_64-w64-mingw32-gcc -o main main.c icon.res `mingw64-pkg-config --cflags gtk+-3.0 --libs gtk+-3.0`

Now the actual .exe file will have an icon associated with it on Windows.
Remove Command Prompt window

Just add the -mwindows flag to your compile command.
Fix Window Decorations

You can disable the GTK client-side decorations by adding the following line to the code:

putenv("GTK_CSD=0");

Now the program should use the normal Windows exit button and drag bar.
Switch to a Windows GTK theme

Adwaita looks bad on Windows. Search Gnome-Look for a different GTK3 theme to use with your app. You can choose a flatter, lighter theme or one specifically made to look like Windows. For this example, I chose the "Windows10" theme.

Download and extract the theme, then copy it to the share/themes/ directory in the windows/ directory we've been using.

Then create a file called settings.ini in a etc/gtk-3.0/ folder (also in the windows/ directory) with the following contents:

[Settings]
gtk-theme-name=Windows10

Now the program should look like native Windows software:

Generate an installer

Here's how to make an installer using a script called nsiswrapper, so your users don't have to manually unzip this windows/ folder. Nsiswrapper generates an NSIS script and optionally compiles it using makensis.

cd into the windows/ directory, and run:

nsiswrapper --run main.exe ./*

This should generate a new file called installer.exe, which you can use to distribute the program. The installer is a standard GUI wizard that Windows users will be accustomed to. It allows users to optionally add a desktop shortcut, start menu entry, and taskbar shortcut.

Notably, it also includes an uninstaller.
Automating builds

You may have noticed that I've been using Fedora to compile this program. I'm actually running Arch Linux, but MinGW packages aren't easily available for Arch, so I've been using a Linux container to take advantage of Fedora's package system.

I'm using Buildah instead of Docker. I wrote a script to automate the following tasks

set up a named Fedora container
    install the necessary packages using dnf
    save the container so I don't have to download dependencies again
    compile the GTK program using the steps I've outlined so far
    generate the installer

Before you look at the script, I recommend reading the buildah introduction tutorial.

#!/bin/bash
setup () {
	# Create a fedora container
	container=$(buildah from fedora)

# Install dependencies
	buildah run $container dnf -y install mingw64-gtk3 mingw32-binutils mingw32-nsiswrapper

# Fix typo in mingw library
	buildah run $container bash -c "sed -i -e 's/-Wl,-luuid/-luuid/g' /usr/x86_64-w64-mingw32/sys-root/mingw/lib/pkgconfig/gdk-3.0.pc"

https://wrycode.com/gtk3-cross-compile/

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Cross-compile a GTK3 app from Linux to Windows with native Windows look and feel28.02.25

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