Fx2D — 2D Rigid Body Physics Engine

A 2D rigid body physics engine written in C++20, using SAT collision detection, XPBD constraint solving, and raylib for rendering.

Examples

Key Features

• SAT collision detection: Efficient circle and polygon collision using the Separating Axis Theorem (SAT)
• XPBD constraint solver: Position-based dynamics with compliance control
• Modern memory management: Safe resource handling with std::shared_ptr / std::unique_ptr
• YAML based scene description: Declarative setup of entities, textures, and physics parameters in .yml files
• FxArray & Math Utilities: NumPy-style FxArray and comprehensive linear-algebra utilities in Fx2D/Math.h
• raylib-based rendering: Lightweight, cross-platform renderer with raylib and ImGui integration

Dependencies

• CMake 3.16+ - Build system generator
• Eigen3 3.3+ - Linear algebra and math operations
• raylib 4.5+ - Scene rendering and graphics
• yaml-cpp - YAML parsing for scene configuration
• ImGui 1.92 - User interface framework
• rlImGui - Raylib-ImGui integration

Installation & Build

The repository keeps lib/imgui and lib/rlImGui as placeholder folders in Git, but it does not commit the third-party sources. Populate those folders locally before building.

Method 1: CMake

cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
cmake --build build -j

Method 2: Using fxmake

chmod +x fxmake       # Make executable
./fxmake              # Build in Release mode
./fxmake debug        # Build in Debug mode
./fxmake rebuild      # Clean and rebuild
./fxmake clean        # Clean build artifacts

Getting Started

Basic Usage

#include "Fx2D/Core.h"

int main() {
    // Load scene from YAML
    auto scene = FxYAML::buildScene("./Scene.yml");

    // Initialize renderer with 60 FPS target
    FxRylbRenderer renderer(scene, 60);
    
    // Start the simulation loop
    renderer.run();
    return 0;
}

For headless simulation, testing, or data collection.

int main() {
    // Load scene from YAML
    auto scene = FxYAML::buildScene("./Scene.yml");

    const double dt = 0.001f;             // Fixed time step in seconds
    auto ball = scene.get_entity("ball"); // Get the poiner to the entity by name "ball"
    for (size_t i = 0; i < 10; ++i) {
        scene.step(dt); // Advance physics without rendering
        std::cout<< ball->pose <<std::endl;  
    }
    return 0;
}

Running Examples

To run an example, copy the main.cpp from examples to src/, build the project, and ensure Scene.yml and assets are accessible to the executable.

./Fx2D      # Linux/macOS
./Fx2D.exe  # Windows

Documentation

Doc	Description
scene_yml.md	Full reference for writing Scene.yml files — scene block, entities, geometry types, physics fields
xpbd_solver.md	How the XPBD solver works — per-substep pipeline, constraint kernel equations, constraint types
collision_resolution.md	Collision detection and response — SAT narrow phase, penetration correction, restitution & friction
raylib_renderer.md	Raylib renderer API — window setup, background, camera, draw callbacks
headless_mode.md	Running the simulation without a renderer for testing and data collection
math_utils.md	FxArray, vector/matrix math utilities, and helper functions
ToDo.md	Current feature and robustness roadmap for Fx2D

Roadmap

See ToDo.md for the current feature and robustness roadmap.

License

BSD-3-Clause License

Contributing

Contributions are welcome! Please follow the existing code style and conventions.

• Bugs & feature requests: Open a new issue describing the problem or proposal clearly (steps to reproduce, or the rationale/use case).
• Working on features/fixes: Create a new branch from main, commit your changes, and open a pull request referencing the issue.