Muli

2D Rigid body physics engine.

Features

Collision

• Continuous collision detection (Bilateral advancement by Erin Catto of Box2D)
• Shapes: circle, capsule, and convex polygon
• Support for rounded polygons
• Multiple colliders attached to a single body
• Dynamic, static, and kinematic bodies
• Collision filtering
• Dynamic AABB tree broadphase
• Raycast, shapecast, and area queries

Physics Simulation

• Continuous physics simulation with time of impact solver
• PGS solver with a separate position correction (PGS NGS)
• Stable stacking with a 2-contact LCP solver (Block solver)
• Persistent constraint graph
• Constraint islanding and sleeping
• Contact callbacks: begin, touching, end, pre-solve, post-solve, and destroy
• Physics material: friction, restitution, and surface speed
• Various joint types: angle, distance, grab, line, motor, prismatic, pulley, revolute, and weld
• Joints with limits and motors

Others

• Cross platform library (C++20)
• Intuitive and straightforward API design

Demo

• 50+ interactive demos
• OpenGL based cross platform demo framework
• WebAssembly powered web demo

Example

#include "muli/muli.h"

using namespace muli;

int main()
{
    WorldSettings settings;
    World world(settings);

    Body* box = world.CreateBox(1.0f);
    box->SetPosition(0.0f, 5.0f);

    // Run simulation for one second
    float dt = 1.0f / 60.0f;
    for(int i = 0; i < 60; ++i)
    {
        world.Step(dt);
    }

    return 0;
}

Building and running the demo

• Install CMake.
• Ensure CMake is in the system PATH.
• Clone the repository: git clone https://github.com/Sopiro/Muli
• Run CMake build script for your system:
  • Visual Studio: Run build.bat.
  • Other systems: Run build.sh.
• You can find the demo executable in build/bin.

Including the library

You can easily include the library using CMake's FetchContent module.

include(FetchContent)

FetchContent_Declare(
    muli
    GIT_REPOSITORY https://github.com/Sopiro/Muli
)

set(MULI_BUILD_DEMO OFF)
FetchContent_MakeAvailable(muli)

Installing the library

You can install the library using these commands:

mkdir build
cd build
cmake -DMULI_BUILD_DEMO=OFF ..
cmake --build . --config Release
cmake --install . --prefix "installation-path"

Assuming you've added "installation-path" to your system PATH, you can now integrate the library into your project.

find_package(muli REQUIRED)

target_link_libraries(your-project PRIVATE muli::muli)

References

Here are some great resources for learning how to build a physics engine:

• https://www.toptal.com/game/video-game-physics-part-i-an-introduction-to-rigid-body-dynamics
• https://allenchou.net/game-physics-series/
• https://box2d.org/publications/
• https://www.cs.cmu.edu/~baraff/sigcourse/index.html
• https://dyn4j.org/blog/