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Box2D is a 2D physics engine for games.

For help with Box2D, please visit There is a forum there where you may post your questions.

Please see Building.txt to learn how to build Box2D and run the testbed.


To run the demos, set Testbed as your startup project and press F5. Some test bed commands are:

  • r to reset the current test
  • SPACE to launch a bomb
  • keys to pan
  • x and z to zoom in/out
  • use the mouse to click and drag objects


Please do not submit pull requests with new features. Instead, please file an issue first for discussion. For bugs, I prefer detailed bug reports over pull requests.



  • Continuous collision detection
  • Contact callbacks: begin, end, pre-solve, post-solve
  • Convex polygons and circles
  • Multiple shapes per body
  • One-shot contact manifolds
  • Dynamic tree broadphase
  • Efficient pair management
  • Fast broadphase AABB queries
  • Collision groups and categories


  • Continuous physics with time of impact solver
  • Persistent body-joint-contact graph
  • Island solution and sleep management
  • Contact, friction, and restitution
  • Stable stacking with a linear-time solver
  • Revolute, prismatic, distance, pulley, gear, mouse joint, and other joint types
  • Joint limits, motors, and friction
  • Momentum decoupled position correction
  • Fairly accurate reaction forces/impulses


  • Small block and stack allocators
  • Centralized tuning parameters
  • Highly portable C++ with no use of STL containers


  • OpenGL with GLFW
  • Graphical user interface with imgui
  • Easily switch between tests using GUI
  • Test framework for easily adding new tests
  • Mouse picking and the bomb!
  • CMake build system files


  • User manual
  • Doxygen document with code comments
  • Active user forum


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

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