physics.js

Vec2 = Box2D.Common.Math.b2Vec2;
BodyDef = Box2D.Dynamics.b2BodyDef;
Body = Box2D.Dynamics.b2Body;
FixtureDef = Box2D.Dynamics.b2FixtureDef;
Fixture = Box2D.Dynamics.b2Fixture;
World = Box2D.Dynamics.b2World;
MassData = Box2D.Collision.Shapes.b2MassData;
PolygonShape = Box2D.Collision.Shapes.b2PolygonShape;
CircleShape = Box2D.Collision.Shapes.b2CircleShape;
DebugDraw = Box2D.Dynamics.b2DebugDraw;
RevoluteJointDef = Box2D.Dynamics.Joints.b2RevoluteJointDef;

PhysicsEngineClass = Class.extend({
    world: null,

    PHYSICS_LOOP_HZ : 1.0 / 60.0,

    //-----------------------------------------
    create: function () {
        gPhysicsEngine.world = new World(
            new Vec2(0, 0), // Gravity vector
            false           // Don't allow sleep
        );
    },

    //-----------------------------------------
    update: function () {
        var start = Date.now();

        gPhysicsEngine.world.Step(
            gPhysicsEngine.PHYSICS_LOOP_HZ,    //frame-rate
            10,    //velocity iterations
            10     //position iterations
        );
        gPhysicsEngine.world.ClearForces();

        return(Date.now() - start);
    },

    //-----------------------------------------
    registerBody: function (bodyDef) {
        var body = gPhysicsEngine.world.CreateBody(bodyDef);
        return body;
    },

    //-----------------------------------------
    addBody: function (entityDef) {
        var bodyDef = new BodyDef();
        
        var BODY_STATES = {
            static: Body.b2_staticBody,
            dynamic: Body.b2_dynamicBody
        };
        
        bodyDef.type = BODY_STATES[entityDef.type];
    
        bodyDef.position.x = entityDef.x;
        bodyDef.position.y = entityDef.y;
        
        var body = gPhysicsEngine.registerBody(bodyDef);

        var fixtureDef = new FixtureDef();
        
        if(entityDef.useBouncyFixture) {
            this.fixtureDef.density = 1.0;
            this.fixtureDef.friction = 0;
            this.fixtureDef.restitution = 1.0;
        }

        var polygonShape = new PolygonShape();
        fixtureDef.shape = polygonShape;

        fixtureDef.shape.SetAsBox(entityDef.halfWidth, entityDef.halfHeight);

        body.CreateFixture(fixtureDef);
        
        return body;
    }
    
    //-----------------------------------------
    removeBody: function (obj) {
        gPhysicsEngine.world.DestroyBody(obj);
    }
});

var gPhysicsEngine = new PhysicsEngineClass();