Nuklear — Minimal ANSI C Immediate-Mode GUI Library

Introduction

Nuklear is a single-header ANSI C GUI library that uses an immediate-mode paradigm to draw user interfaces. It has no dependencies, no default rendering backend, and no platform-specific code, making it ideal for embedding in games, tools, embedded systems, and any C or C++ project that needs a lightweight UI without pulling in a heavy framework.

What Nuklear Does

• Provides a complete widget set (buttons, sliders, text input, trees, tabs, groups) in one C header file
• Uses immediate-mode rendering: UI is declared every frame, no persistent widget objects to manage
• Outputs abstract draw commands that you feed to any rendering backend (OpenGL, Vulkan, DirectX, SDL, etc.)
• Compiles on any platform with an ANSI C89 compiler, including embedded targets
• Supports custom memory allocators, UTF-8 text, and user-defined widget skinning

Architecture Overview

Nuklear operates as a stateless command buffer generator. Each frame, application code calls Nuklear functions to describe the UI layout and widgets. Nuklear processes input, calculates layout, and emits a list of draw commands (rectangles, triangles, text, images) into a command buffer. A platform-specific backend then iterates this buffer and submits the actual draw calls. This separation means Nuklear itself has zero platform or graphics API dependencies.

Self-Hosting & Configuration

• Copy nuklear.h into your project; define NK_IMPLEMENTATION in exactly one translation unit
• Choose a rendering backend from the demo/ directory (SDL, GLFW, X11, GDI, Allegro, SFML, etc.) or write your own
• Configure font rendering by loading a TTF font with the built-in font baker or supply your own font atlas
• Control memory allocation by passing custom nk_allocator structs for heap-free or pool-based allocation
• Adjust styling through the nk_style struct: colors, padding, rounding, and spacing are fully configurable

Key Features

• Single-header library: one file to include, no build system integration needed
• Pure ANSI C89 with no dependencies — compiles with GCC, Clang, MSVC, and embedded toolchains
• Built-in layout engine with row-based, space-based, and custom layout modes
• Font baking utility for TTF fonts with configurable glyph ranges and atlas packing
• Permissive dual-licensed under MIT and Public Domain

Comparison with Similar Tools

• Dear ImGui — C++ immediate-mode GUI; Nuklear is pure C89 and single-header, better for C projects and embedded targets
• Raygui — Immediate-mode GUI for raylib; Nuklear is renderer-agnostic and works with any graphics backend
• egui — Rust immediate-mode GUI; Nuklear targets the C/C++ ecosystem
• Microui — Even smaller immediate-mode library; Nuklear offers a richer widget set and built-in font baking
• GTK/Qt — Retained-mode heavyweight frameworks; Nuklear is orders of magnitude smaller with no runtime dependencies

FAQ

Q: How do I render Nuklear output? A: Nuklear produces abstract draw commands. You write a small backend (or use an included demo backend) that translates these commands into your graphics API's draw calls.

Q: Is Nuklear suitable for game engine editor UIs? A: Yes. Its immediate-mode design and renderer independence make it popular for game engine tooling and in-game debug overlays.

Q: Can I use Nuklear from languages other than C? A: Community bindings exist for Python, Go, Rust, Lua, and others, though the primary API is C.

Q: Does Nuklear handle high-DPI displays? A: You control scaling by adjusting font size and the global scale factor. The library does not auto-detect DPI, giving you full control.

Sources

• https://github.com/Immediate-Mode-UI/Nuklear
• https://immediate-mode-ui.github.io/Nuklear/