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    JavaScript 2D physics library
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    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

    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
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