How to Install and Test gThumb 4.0 Alpha with GTK4 and Libadwaita

Introduction

gThumb, the versatile open-source image viewer and organizer, has undergone a major transformation. The latest alpha release of gThumb 4.0 has been rewritten in Vala and ported to the modern GTK4 and Libadwaita toolkit. This overhaul brings a sleek, refreshed interface that looks and feels completely different from its predecessor. Beyond visual changes, the alpha introduces support for WEBP and animated PNGs, the ability to export images in the JXL format, and a handy censor filter for pixelating or blurring parts of an image. If you're curious to test these new features and experience the redesigned gThumb, this step-by-step guide will help you get started safely and efficiently.

What You Need

• A Linux distribution (preferably Ubuntu or a Debian-based system) – the alpha is built primarily for Linux, though you may adapt steps for other OSes with caution.
• Basic familiarity with the command line (terminal) and package management.
• A working internet connection for downloading the alpha release and dependencies.
• sufficient disk space for building from source (approx. 1–2 GB) if you opt for compiling.
• Optional: a virtual machine or separate testing environment to avoid affecting your production system.

Step-by-Step Guide

Step 1: Prepare Your System

Before you begin, update your package list and ensure your system has the fundamental build tools. Open a terminal and run:

sudo apt update
sudo apt upgrade -y

Install the required development packages for GTK4, Libadwaita, and Vala:

sudo apt install build-essential meson ninja-build valac libgtk-4-dev libadwaita-1-dev libglib2.0-dev libexif-dev libtiff-dev liblcms2-dev libjpeg-dev libpng-dev libwebp-dev libjxl-dev libraw-dev libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev

Note: Some distributions may name packages differently (e.g., libadwaita-1-dev might be libadwaita-1.0-dev). Adjust based on your package manager.

Step 2: Download the gThumb 4.0 Alpha Source

The alpha is available from the official gThumb repository. You can either clone the Git branch or download a tarball. For the latest alpha, use Git:

git clone -b gthumb-4.0-alpha https://gitlab.gnome.org/GNOME/gthumb.git
cd gthumb

Alternatively, visit the releases page to download the alpha tarball and extract it.

Step 3: Configure and Build the Application

gThumb uses the Meson build system. Create a build directory and run configuration:

meson setup build

If any dependencies are missing, Meson will warn you. Install them using your package manager and re-run configuration. Once configuration succeeds, compile the application:

meson compile -C build

This process may take several minutes. If you encounter errors, check that all required libraries are installed and their versions match the alpha's requirements.

Step 4: Install the Alpha Build (Optional but Recommended)

To use gThumb 4.0 system-wide without interfering with stable installations, you can install it to a custom prefix. For testing, it's easier to install in your home directory:

meson install -C build --destdir ~/gthumb-install

Then copy or symlink the binary to a location in your PATH. Alternatively, you can run it directly from the build directory without full installation:

./build/gthumb

Step 5: Launch gThumb 4.0 and Explore the New Interface

Run the command gthumb (or the path to your built binary). The first thing you'll notice is the dramatically revamped UI. The window now features a more polished, flat design with rounded corners and a unified toolbar, following Libadwaita’s guidelines. Navigate through your image folders – the thumbnail view, sidebar, and menus all feel modern and responsive.

To truly appreciate the changes, open an old GTK3 version of gThumb (if you have it installed separately) and compare. You'll see a transformation from a dated interface to a clean, contemporary look that blends seamlessly with GNOME 42+ desktops.

Step 6: Test New Features

With the alpha running, you can verify the promised enhancements:

• WEBP and Animated PNG Support: Open a .webp or .apng file. gThumb should display the image and, for animations, play them automatically. Use the playback controls in the toolbar if needed.
• Export to JXL (JPEG XL): Open any image, go to File > Export, and choose JPEG XL as the format. Adjust quality settings and export. This feature offers superior compression for high-quality images.
• Censor Filter: Select an image, then click on Tools > Censor. A toolbar appears with options to pixelate or blur. Click and drag over areas you want to obscure – perfect for anonymizing faces or sensitive details.

Step 7: Report Bugs and Provide Feedback

As an alpha release, you may encounter instability or missing features. If you find a bug, report it on the gThumb GitLab issues page. Include your system details (OS version, gThumb version from Help > About) and steps to reproduce. Your feedback helps developers refine the application before the stable release.

Tips for a Smooth Experience

• Back up your image library: Though gThumb is unlikely to corrupt files, it's wise to test with a copy of your photos rather than your primary collection.
• Use a separate environment: Consider running the alpha in a Flatpak sandbox or a virtual machine to avoid affecting your daily workflow. A dedicated user account can also suffice.
• Keep an eye on official announcements: The gThumb team provides updates on the repository and via OMG! Ubuntu's coverage. Follow to learn about subsequent alpha releases and release candidates.
• Learn keyboard shortcuts: The new UI introduces a different set of shortcuts. Press Ctrl+? or view the Help menu to find them – they'll speed up your workflow.
• Be patient with crashes: Alpha software is unstable. Save your work frequently and restart gThumb if it freezes. Check the terminal for error messages that can aid debugging.