Box2D

Box2D is a 2D physics engine for games.

Build Status

Features

Collision

• Continuous collision detection
• Contact events
• Convex polygons, capsules, circles, rounded polygons, segments, and chains
• Multiple shapes per body
• Collision filtering
• Ray casts, shape casts, and overlap queries
• Sensor system

Physics

• Robust Soft Step rigid body solver
• Continuous physics for fast translations and rotations
• Island based sleep
• Revolute, prismatic, distance, motor, weld, and wheel joints
• Joint limits, motors, springs, and friction
• Joint and contact forces
• Body movement events and sleep notification

Character movement

• Geometric mover with robust plane solver
• Dynamic mover with custom joint support

System

• Data-oriented design
• Written in portable C17
• Extensive multithreading and SIMD
• Optimized for large piles of bodies
• Low cost double-precision support for large worlds
• Recording and replay
• Cross platform determinism
• Snapshot and restore

Samples

• OpenGL with GLFW
• Graphical user interface with imgui
• Many samples to demonstrate features and performance

Building All Platforms

• Install CMake
• Install git
• Ensure these run from the command line

Building with CMake presets

The presets in CMakePresets.json give one build flow on every platform and are picked up automatically by Visual Studio, VS Code, and CLion (open the folder and choose a preset). From the command line:

• Windows: cmake --preset windows then cmake --build --preset windows-release
• Linux: cmake --preset linux-release then cmake --build --preset linux-release
• macOS: cmake --preset macos then cmake --build --preset macos-release

Use the *-debug build presets for a debug build (not recommended for the replay viewer). The presets use the default native toolchain (the installed Visual Studio on Windows, Make on Linux, Xcode on macOS), so no specific compiler version is required.

Building for Visual Studio

• Install Visual Studio
• Run build_vs2026.bat for Visual Studio 2026, or use the windows preset above for other versions
• Open and build the generated solution in the build folder

Building for Linux

• Run build.sh from a bash shell
• Results are in the build sub-folder

Building for Xcode

• mkdir build
• cd build
• cmake -G Xcode ..
• Open box2d.xcodeproj
• Select the samples scheme
• Build and run the samples

Building and installing

• mkdir build
• cd build
• cmake ..
• cmake --build . --config Release
• cmake --install . (might need sudo)

Installing also provides a pkg-config file, so pkg-config --modversion box2d reports the installed version and pkg-config --cflags --libs box2d gives the build flags.

Building with zig

Fetch and link Box2D from a Zig project:

• zig fetch --save git+https://github.com/erincatto/box2d

In build.zig:

const box2d_dep = b.dependency("box2d", .{});
exe.root_module.addImport("box2d", box2d_dep.module("box2d"));

In Zig code, start using box2d

const box2d = @import("box2d");

pub fn main() void {
    var world_def = box2d.b2DefaultWorldDef();
    world_def.gravity.y = -10.0;
    const world_id = box2d.b2CreateWorld(&world_def);
    defer box2d.b2DestroyWorld(world_id);

    box2d.b2World_Step(world_id, 1.0 / 60.0, 4);
}

Building with Swift Package Manager

Add box2d as a dependency in your Package.swift:

.package(url: "https://github.com/erincatto/box2d.git", branch: "main")

And add the product to your target:

.target(
    name: "MyGame",
    dependencies: [.product(name: "box2d", package: "box2d")]
),

In Swift code, the C API is imported directly:

import box2d

var worldDef = b2DefaultWorldDef()
let worldId = b2CreateWorld(&worldDef)

C structs are passed as inout arguments using &.

Replay viewer

The samples app doubles as a viewer for Box2D recordings (.b2rec files). Any preset above builds it. Pass a recording on the command line to open it directly:

• Windows: build\bin\Release\samples.exe path\to\session.b2rec
• Linux: build/bin/samples path/to/session.b2rec
• macOS: build/bin/Release/samples path/to/session.b2rec

On Windows you can also drag a .b2rec file onto samples.exe. The viewer runs from any directory. Without an argument, open a recording from the Replay menu. See docs/recording.md for how to make a recording.

Compatibility

The Box2D library and samples build and run on Windows, Linux, and Mac.

You will need a compiler that supports C17 to build the Box2D library.

You will need a compiler that supports C++20 to build the samples.

Box2D uses SSE2, AVX2, and Neon (AArch64) SIMD math to improve performance. This can be disabled by defining BOX2D_DISABLE_SIMD. SSE2 is automatically used as a fallback when the CPU doesn't support AVX2.

Documentation

• Manual

Community

• Discord

Contributing

Please do not submit pull requests. Instead, please file an issue for bugs or feature requests. For support, please visit the Discord server.

Giving feedback

Please file an issue or start a chat on discord. You can also use GitHub Discussions.

License

Box2D is developed by Erin Catto and uses the MIT license.

Sponsorship

Support development of Box2D through Github Sponsors.

Please consider starring this repository and subscribing to my YouTube channel.

LLM Usage

LLMs are used in the following areas:

• unit tests
• samples app
• migrating code between Box2D and Box3D
• build configuration
• code reviews
• benchmarking

Elsewhere all code is developed and written by me.

External ports, wrappers, and bindings (unsupported)

• Beef bindings - https://github.com/EnokViking/Box2DBeef
• C++ bindings - https://github.com/HolyBlackCat/box2cpp
• WASM - https://github.com/Birch-san/box2d3-wasm