JavaScript 2D physics library
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Stefan Hedman
Latest commit 2beb275 Apr 8, 2018

README.md

p2.js

2D rigid body physics engine written in JavaScript. Includes collision detection, contacts, friction, restitution, motors, springs, advanced constraints and various shape types.

Demos | Examples | Documentation | Download | CDN | Wiki

Featured projects using p2.js

Demos

These demos use the p2 Demo framework, which provides rendering and interactivity. Use mouse/touch to throw or create objects. Use the right menu (or console!) to tweak parameters. Or just check the source to see how to programmatically build the current scene using p2.

Examples

Examples showing how to use p2.js with your favorite renderer.

Sample code

The following example uses the World, Circle, Body and Plane classes to set up a simple physics scene with a ball on a plane.

// Create a physics world, where bodies and constraints live
var world = new p2.World({
    gravity:[0, -9.82]
});

// Create an empty dynamic body
var circleBody = new p2.Body({
    mass: 5,
    position: [0, 10]
});

// Add a circle shape to the body
var circleShape = new p2.Circle({ radius: 1 });
circleBody.addShape(circleShape);

// ...and add the body to the world.
// If we don't add it to the world, it won't be simulated.
world.addBody(circleBody);

// Create an infinite ground plane body
var groundBody = new p2.Body({
    mass: 0 // Setting mass to 0 makes it static
});
var groundShape = new p2.Plane();
groundBody.addShape(groundShape);
world.addBody(groundBody);

// To animate the bodies, we must step the world forward in time, using a fixed time step size.
// The World will run substeps and interpolate automatically for us, to get smooth animation.
var fixedTimeStep = 1 / 60; // seconds
var maxSubSteps = 10; // Max sub steps to catch up with the wall clock
var lastTime;

// Animation loop
function animate(time){
	requestAnimationFrame(animate);

    // Compute elapsed time since last render frame
    var deltaTime = lastTime ? (time - lastTime) / 1000 : 0;

    // Move bodies forward in time
    world.step(fixedTimeStep, deltaTime, maxSubSteps);

    // Render the circle at the current interpolated position
    renderCircleAtPosition(circleBody.interpolatedPosition);

    lastTime = time;
}

// Start the animation loop
requestAnimationFrame(animate);

To interact with bodies, you need to do it after each internal step. Simply attach a "postStep" listener to the world, and make sure to use body.position here - body.interpolatedPosition is only for rendering.

world.on('postStep', function(event){
    // Add horizontal spring force
    circleBody.force[0] -= 100 * circleBody.position[0];
});

Install

Browser

Download either p2.js or the minified p2.min.js and include the script in your HTML:

<script src="p2.js" type="text/javascript"></script>

If you would like to use ordinary Array instead of Float32Array, define P2_ARRAY_TYPE globally before loading the library.

<script type="text/javascript">P2_ARRAY_TYPE = Array;</script>
<script src="p2.js" type="text/javascript"></script>
Node.js
npm install p2

Then require it like so:

var p2 = require('p2');

Supported collision pairs

Circle Plane Box Convex Particle Line Capsule Heightfield Ray
Circle Yes - - - - - - - -
Plane Yes - - - - - - - -
Box Yes Yes Yes - - - - - -
Convex Yes Yes Yes Yes - - - - -
Particle Yes Yes Yes Yes - - - - -
Line Yes Yes (todo) (todo) - - - - -
Capsule Yes Yes Yes Yes Yes (todo) Yes - -
Heightfield Yes - Yes Yes (todo) (todo) (todo) - -
Ray Yes Yes Yes Yes - Yes Yes Yes -

Note that concave polygon shapes can be created using Body.fromPolygon.

Install

Make sure you have git, Node.js, NPM and grunt installed.

git clone https://github.com/schteppe/p2.js.git;
cd p2.js;
npm install; # Install dependencies
grunt;

Grunt tasks

List all tasks using grunt --help.

grunt        # Run tests, build, minify
grunt dev    # Run tests, build
grunt test   # Run tests
grunt yuidoc # Build docs
grunt watch  # Watch for changes and run the "dev" task

Release process

  1. Bump version number.
  2. Build and commit files in build/ and docs/.
  3. Tag the commit with the version number e.g. vX.Y.Z
  4. Add relase notes to github
  5. Publish to NPM