Muli

2D Rigidbody 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 shapes attached to a single body
• Dynamic, static and kinematic bodies
• Collision filtering
• Dynamic AABB tree broadphase
• Dynamic tree accelerated raycast, shapecast and world query
• Easy-to-use collision detection and distance funtions

Physics Simulation

• Continuous physics simulation (Time of impact solver and sub-stepping)
• Efficient and persistent contact management from box2d
• Constraint islanding and sleeping
• Stable stacking with 2-contact LCP solver (Block solver)
• Decoupled position correction iteration
• Contact callbacks: begin, touching, end, pre-solve, post-solve and destroy event
• Physics material: friction, restitution and surface speed
• Various joints: angle, distance, grab, line, motor, prismatic, pulley, revolute and weld

ETC

• 50+ Demos
• OpenGL based demo framework
• Cross platform library
• Intuitive and straightforward API
• Utilizes specialized memory allocators

Example

#include "muli/muli.h"

using namespace muli;

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

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

Installation

You can install the library using this 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)

Todo

• Implement position solve step for joints
• Multithreading

References

Here are some great resources to learn 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/