Add initial prototype.

3-mid/physics/implement/box2d/contrib/README.md

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+![Box2D Logo](https://box2d.org/images/logo.svg)
+
+# Build Status
+[![Build Status](https://travis-ci.org/erincatto/box2d.svg?branch=master)](https://travis-ci.org/erincatto/box2d)
+
+# Box2D 
+
+Box2D is a 2D physics engine for games.
+
+## Contributing
+
+Please do not submit pull requests with new features or core library changes. Instead, please file an issue first for discussion. For bugs, I prefer detailed bug reports over pull requests.
+
+## Features
+
+### Collision
+- 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
+
+### Physics
+- 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
+
+### System
+- Small block and stack allocators
+- Centralized tuning parameters
+- Highly portable C++ with no use of STL containers
+
+### Testbed
+- OpenGL with GLFW
+- Graphical user interface with imgui
+- Extensible test framework
+- Support for loading world dumps
+
+## Building
+- Install [CMake](https://cmake.org/)
+- Ensure CMake is in the user `PATH`
+- Visual Studio: run `build.bat` from the command prompt
+- Otherwise: run `build.sh` from a bash shell
+- Results are in the build sub-folder
+- On Windows you can open box2d.sln
+
+## Building Box2D - Using vcpkg
+You can download and install Box2D using the [vcpkg](https://github.com/Microsoft/vcpkg) dependency manager:
+
+- git clone https://github.com/Microsoft/vcpkg.git
+- cd vcpkg
+- ./bootstrap-vcpkg.sh
+- ./vcpkg integrate install
+- ./vcpkg install box2d
+
+The Box2D port in vcpkg is kept up to date by Microsoft team members and community contributors. If the version is out of date, please [create an issue or pull request](https://github.com/Microsoft/vcpkg) on the vcpkg repository.
+
+Note: vcpkg support is not provided by the Box2D project
+
+## Building for Xcode
+- Install [CMake](https://cmake.org)
+- Add Cmake to the path in .zprofile (the default Terminal shell is zsh)
+    - export PATH="/Applications/CMake.app/Contents/bin:$PATH"
+- mkdir build
+- cd build
+- cmake -G Xcode ..
+- open box2d.xcodeproj
+- Select the testbed scheme
+- Edit the scheme to set a custom working directory, make this be in box2d/testbed
+- You can now build and run the testbed
+
+## Installing using CMake
+You can use the CMake install feature to deploy the library to a central location that can
+be accessed using:
+```
+find_package(box2d REQUIRED)
+target_link_libraries(mytarget PRIVATE box2d)
+```
+You can build and install the library and docs using this command sequence (requires Doxygen):
+```
+mkdir build
+cd build
+cmake -DBOX2D_BUILD_DOCS=ON ..
+cmake --build .
+cmake --build . --target INSTALL
+```
+On Windows this tries to install in `Program Files` and thus requires admin privileges. Alternatively you can target another directory using something like this:
+```
+mkdir build
+cd build
+cmake -DBOX2D_BUILD_DOCS=ON -DCMAKE_INSTALL_PREFIX="C:/packages" ..
+cmake --build .
+cmake --build . --target INSTALL
+```
+
+## Documentation
+- [Manual](https://box2d.org/documentation/)
+- [reddit](https://www.reddit.com/r/box2d/)
+- [Discord](https://discord.gg/NKYgCBP)
+
+## License
+Box2D is developed by Erin Catto, and uses the [MIT license](https://en.wikipedia.org/wiki/MIT_License).
+
+## Sponsorship
+Support development of Box2D through [Github Sponsors](https://github.com/sponsors/erincatto)