Flex is a flexible box layout system written in C, designed to be easy to consume from other languages
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flex is a flexible box layout system following the CSS flexbox module specifications. The goal is to offer a fully compliant implementation with a small and maintainable code base under a permissive license.

flex exposes a plain C API with the same parameters that you would use in CSS to customize the layout of a flexible view hierarchy. The API is designed to be easily interoperable with foreign runtimes (ex. C#) and meant to be used by widget toolkits as the foundation of a view layout API.

flex supports both single and multiple (wrap) lines layouts.

Getting Started

If you program in C# you can go straight to the bindings/csharp directory.

If you program in a C-compatible environment you can simply copy the flex.c and flex.h files to your project. The code was written to be cross-platform and does not require dependencies.

On a Mac you can also generate static and dynamic libraries for iOS, Android and macOS using make:

$ make macos
$ make ios
$ make android
$ make             # builds everything

Make sure to have the ANDROID_NDK environment variable set to the path where the Android NDK is located in your system. You can also tweak build variables by editing the Makefile file.

On a Windows machine you can generate dynamic libraires (DLL) for x86, x64, ARM and ARM64 by opening the Visual Studio project file or running msbuild from the command line.

Demo App

Under the demo directory you will find an Xcode project that will build a Mac demo app. The app exposes the entire set of flexbox parameters that are implemented and lets you create views (including nested ones), similar to how you would build a more realistic user interface in practice.

Implementation Status

Attribute Status
width, height πŸ†—
self_sizing πŸ†—
padding πŸ†—
margin πŸ†—
justify_content flex_start πŸ†—
justify_content flex_end πŸ†—
justify_content center πŸ†—
justify_content space_around πŸ†—
justify_content space_between πŸ†—
justify_content space_evenly πŸ†—
align_content flex_start πŸ†—
align_content flex_end πŸ†—
align_content center πŸ†—
align_content space_around πŸ†—
align_content space_between πŸ†—
align_content space_evenly πŸ†—
align_content stretch πŸ†—
align_items flex_start πŸ†—
align_items flex_end πŸ†—
align_items center πŸ†—
align_items stretch πŸ†—
align_self flex_start πŸ†—
align_self flex_end πŸ†—
align_self center πŸ†—
align_self stretch πŸ†—
position relative πŸ†—
position absolute πŸ†—
direction column πŸ†—
direction column_reverse πŸ†—
direction row πŸ†—
direction row_reverse πŸ†—
wrap no_wrap πŸ†—
wrap wrap πŸ†—
wrap wrap_reverse πŸ†—
grow πŸ†—
shrink πŸ†—
order πŸ†—
basis πŸ†—


There is a test suite in the tests directory. See the tests/README.md file for more details on how to build, run and contribute to the test suite.


flex is distributed under the terms of the MIT license. See the LICENSE.txt file for more information.