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What is this ?

This is Go a port of Box2D (, a 2D physics engine for games written in C++ by Erin Catto.

The port is complete and based on the latest Box2D commit as of 2017-09-20 (

Who did this ?

The ByteArena team did. Erin Catto, the author of the original software, was not involved in the port.


We kept the source code as close to the C++ as we possibly could. So the documentation you'll find on Box2D is relevant.

API changes

The API had to change a tiny bit due to the fact that :

  • Go has no constructors as a language feature, thus code for constructors has been placed in Make$NAME_OF_TYPE functions
  • Go has no support for function overloading; some functions implemented multiple times for different sets of parameters under the same name in C++ are distinguished by name in the golang version; we tried to make names explicit so that should not be an issue
  • Go has no support for operator overloading; this C++ feature is used extensively throughout the C++ version of Box2D (mainly for the vector and matrix arithmethic), and has been converted to good old, albeit verbose function calls


No opengl testbed for the moment.

Our tests verify the output of position and rotation of bodies over time against those generared by the C++ reference.

Right now, there's a test (passing) checking all the supported body shape collisions in cmd/test-character-collision.

Usage example

Have a look at cpp_compliance_test.go.

License of the original Box2D (C++)

The original Box2D is developed by Erin Catto, and has the zlib license. Thank you Erin for this incredible piece of software.

License of this port (Go)

Box2D.go is developed by ByteArena (, and has the zlib license. While the zlib license does not require acknowledgement, we encourage you to give credit to Box2D.go in your product.