Thulium

Thulium is a Paint.Net alternative/clone for Linux. It supports nearly every feature from original Paint.Net, except plugin support.

Thulium

A fast, lightweight, and cross-platform raster image editor written in native C++17 with Qt 6 and a hardware-accelerated Vulkan rendering pipeline.

Overview

Thulium is designed to provide an intuitive, responsive, and distraction-free raster editing experience. Bridging the gap between overly simplistic paint tools and heavy, complex digital creation suites, Thulium prioritizes speed, clarity, and instant startup.

Inspired by the accessible workflows of classic raster editors like Paint.NET, Thulium is a clean-room reimplementation engineered from scratch to run natively across modern operating systems.

Architecture & Technology

Thulium is architected with performance, modularity, and cross-platform longevity at its core:

Native C++17 Engine: Zero managed runtime overhead, tight memory control, and optimal CPU cache utilization for responsive brush strokes and layer operations.
Dual Rendering Pipeline:
- Hardware-Accelerated Vulkan Backend: Direct GPU rendering for canvas blitting, zoom, pan, and real-time viewport transformations.
- Optimized Software Fallback: CPU-based rasterization engine ensuring compatibility on any display server or headless virtual environment.
Qt 6 Desktop Architecture: Clean, modular UI utilizing modern Qt 6 widgets, dockable tool palettes, non-blocking asynchronous operations, and high-DPI scaling.
Clean-Room Interoperability: Native reader and writer for the Paint.NET (.pdn / PDN3) document format, alongside full support for industry-standard formats including PNG, JPEG, WebP, BMP, and GIF.
Non-Destructive Layer System: Full support for multi-layer composition, opacity controls, standard layer blend modes, and an undo/redo command history stack.

Building from Source

Prerequisites

C++17 compatible compiler (GCC 9+, Clang 10+, or MSVC 2019+)
CMake (>= 3.16)
Qt 6 (Core, Gui, Widgets, Svg)
Vulkan SDK & Loader
ZLIB & GIF libraries

Build Instructions

# Configure the build directory
cmake -B build -S . -DCMAKE_BUILD_TYPE=Release

# Compile using all available CPU cores
cmake --build build -j$(nproc)

# Run Thulium
./build/thulium

Running Tests

ctest --test-dir build --output-on-failure

Building & Installing with Nix

# Build Thulium
nix build

# Run directly without installing
nix run

# Install into your user profile
nix profile install .

# Enter an interactive development shell
nix develop

License & Trademarks

License

Trademarks & Disclaimers

Paint.NET is a registered trademark of Rick Brewster and dotPDN LLC. Thulium is an independent, clean-room project and is not affiliated with, endorsed by, or sponsored by dotPDN LLC.
Qt is a registered trademark of The Qt Company Ltd. and its subsidiaries.
Vulkan and the Vulkan logo are registered trademarks of the Khronos Group Inc.

Finn Freitag @FinnFreitag

Hobby programmer, nature lover, perpetual learner. 🌿

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