RmlUi is a C++ user interface library that renders HTML and CSS-like markup for games and applications.
RmlUi solves the problem of building rich, styled user interfaces in C++ projects without embedding a full web browser. It parses XHTML and CSS source files, applies layout calculations through its own engine, and generates vertices, indices, and draw commands that the host application renders using its own graphics backend. The library maintains full access to the DOM, supports event handling, and can be scripted through optional language plugins. By keeping dependencies minimal and compiling to a fraction of the size of a browser engine, it targets projects where a lightweight UI solution is essential.
RmlUi suits game developers and application creators who need cross-platform interface capabilities without the overhead of web technologies. It works well in real-time applications where the host controls the update loop and rendering pipeline. The library supports most CSS2 features plus selected CSS3 additions like animations, transforms, flexbox, media queries, and filters. Projects should author documents specifically for RmlUi rather than expecting full web compatibility, though web design skills transfer directly. The tool provides a control set including buttons, sliders, and dropdowns, along with a decorator engine for custom visual effects and a runtime visual debugging suite.
The project maintains active development with regular commits addressing bug fixes and feature additions. The codebase shows consistent refinement of the layout engine and rendering pipeline. Documentation is actively maintained and kept current with library changes. The maintainer engages with the community through issue responses and incorporates user feedback into the roadmap.
