2D Physics Engine

A lightweight, flexible 2D physics engine built with TypeScript, featuring an Entity-Component-System (ECS) architecture. Perfect for building 2D games, simulations, and interactive applications.

Features

• 🎮 ECS Architecture - Clean separation of concerns with Entity-Component-System pattern
• 🚀 Rigidbody Physics - Mass, velocity, forces, friction, and restitution
• 💥 Collision Detection - Circle-to-circle collision detection with penetration resolution
• 🎨 Rendering System - Built-in canvas-based rendering with custom drawers
• 🎯 Input Management - Keyboard and mouse input handling
• 📐 Math Utilities - Vector2, AABB, and QuadTree for spatial operations
• 🔧 TypeScript - Fully typed for better development experience
• ⚡ Fixed Timestep - Stable physics simulation with configurable timestep

⚠️ Note: This project is not production-ready. It is still under active development and primarily built for educational purposes, experimentation, and learning how 2D physics engines and ECS architectures work. Use it as a learning tool or prototype, but it may contain bugs, incomplete features, and performance limitations.

Installation

npm install 2d-physics-engine
# or
yarn add 2d-physics-engine
# or
pnpm add 2d-physics-engine

Quick Start

import {
    Iterator,
    Scene,
    Entity,
    Transform,
    Rigidbody,
    CircleCollider,
    Vector2,
    InputManager,
} from '2d-physics-engine';

// Setup canvas
const canvas = document.getElementById('canvas') as HTMLCanvasElement;
const ctx = canvas.getContext('2d')!;
const inputManager = new InputManager();

// Create engine
const engine = new Iterator(inputManager, canvas, ctx);

// Create scene
const scene = new Scene();

// Create an entity with physics
const ball = new Entity('Ball');
ball.addComponent(new Transform(new Vector2(100, 100)));
ball.addComponent(new Rigidbody({ mass: 1, restitution: 0.8, friction: 0.1 }));
ball.addComponent(new CircleCollider(25));

scene.addEntity(ball);

// Start the engine
engine.setScene(scene);
engine.start();

Core Concepts

Entity-Component-System

• Entity: Container for components (e.g., a ball, player, wall)
• Component: Data container (Transform, Rigidbody, Collider)
• System: Logic that operates on entities with specific components

Components

Transform

Handles position, rotation, and scale of entities.

const transform = new Transform(
    new Vector2(100, 100), // position
    0, // rotation (radians)
    new Vector2(1, 1), // scale
);

Rigidbody

Adds physics properties to an entity.

const rigidbody = new Rigidbody({
    mass: 1, // mass in kg
    restitution: 0.8, // bounciness (0-1)
    friction: 0.1, // friction coefficient
});

Colliders

Define collision shapes for entities.

const collider = new CircleCollider(25); // radius

Math Utilities

Vector2

2D vector operations for position, velocity, forces, etc.

import { Vector2 } from '2d-physics-engine';

const v1 = new Vector2(10, 20);
const v2 = new Vector2(5, 5);

// Operations (all return new vectors, immutable)
const sum = v1.add(v2);
const diff = v1.subtract(v2);
const scaled = v1.scale(2);
const normalized = v1.getNormal();
const magnitude = v1.getMagnitude();

AABB

Axis-Aligned Bounding Box for spatial queries.

import { AABB, Vector2 } from '2d-physics-engine';

const box = new AABB(
    new Vector2(0, 0), // min corner
    new Vector2(100, 100), // max corner
);

// Or use factory methods
const box2 = AABB.fromCenter(new Vector2(50, 50), new Vector2(25, 25));

API Reference

Core Classes

• Entity - Container for components
• Scene - Manages collections of entities
• Iterator - Main game loop and system manager
• InputManager - Handles keyboard and mouse input

Components

• Transform - Position, rotation, scale
• Rigidbody - Physics properties
• Collider (abstract) - Collision shape base class
• CircleCollider - Circular collision shape
• Controller - WASD/Arrow key movement controller
• Drawer (abstract) - Rendering base class
• CircleDrawer - Renders circles

Systems

• Physics - Handles physics simulation
• Rendering - Renders entities with drawer components
• CollisionDetector - Detects collisions between entities
• CollisionResolver - Resolves collisions

Math

• Vector2 - 2D vector class
• AABB - Axis-Aligned Bounding Box
• QuadTree - Spatial partitioning structure

Examples

Adding Forces

const rigidbody = entity.getComponent(Rigidbody);
if (rigidbody) {
    rigidbody.addForce(new Vector2(100, 0)); // Apply force to the right
}

Custom Drawer

import { Drawer, Transform } from '2d-physics-engine';

class MyDrawer extends Drawer {
    draw(ctx: CanvasRenderingContext2D, transform: Transform): void {
        // Your custom rendering code
    }
}

Custom Collider

import { Collider, AABB, Transform } from '2d-physics-engine';

class BoxCollider extends Collider {
    static readonly COLLIDER_ID = Symbol('BoxCollider');
    readonly colliderId = BoxCollider.COLLIDER_ID;

    constructor(
        private width: number,
        private height: number,
    ) {
        super();
    }

    getAABB(transform: Transform): AABB {
        // Return AABB based on transform
    }

    calculateInertia(mass: number): number {
        // Calculate moment of inertia
    }
}

Development

# Install dependencies
npm install

# Run development server
npm run dev

# Build library
npm run build:lib

# Run tests
npm test

# Format code
npm run format

License

MIT

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

Resources

• Dot Product
• Cross Product
• 2D Collisions
• Coefficient of Restitution