code: function () {
      var data = this.data;
  
      // If true, show wireframes around physics bodies.
      this.debug = data.debug;
  
      this.callbacks = {beforeStep: [], step: [], afterStep: []};
  
      this.listeners = {};
  
      this.driver = null;
      switch (data.driver) {
        case 'local':
          this.driver = new LocalDriver();
          break;
  
        case 'network':
          this.driver = new NetworkDriver(data.networkUrl);
          break;
  
        case 'worker':
          this.driver = new WorkerDriver({
            fps: data.workerFps,
            engine: data.workerEngine,
            interpolate: data.workerInterpolate,
            interpolationBufferSize: data.workerInterpBufferSize,
            debug: data.workerDebug
          });
          break;
  
        default:
          throw new Error('[physics] Driver not recognized: "%s".', data.driver);
      }
  
      this.driver.init({
        quatNormalizeSkip: 0,
        quatNormalizeFast: false,
        solverIterations: data.iterations,
        gravity: data.gravity
      });
  
      this.driver.addMaterial({name: 'defaultMaterial'});
      this.driver.addMaterial({name: 'staticMaterial'});
      this.driver.addContactMaterial('defaultMaterial', 'defaultMaterial', {
        friction: data.friction,
        restitution: data.restitution,
        contactEquationStiffness: data.contactEquationStiffness,
        contactEquationRelaxation: data.contactEquationRelaxation,
        frictionEquationStiffness: data.frictionEquationStiffness,
        frictionEquationRegularization: data.frictionEquationRegularization
      });
      this.driver.addContactMaterial('staticMaterial', 'defaultMaterial', {
        friction: 1.0,
        restitution: 0.0,
        contactEquationStiffness: data.contactEquationStiffness,
        contactEquationRelaxation: data.contactEquationRelaxation,
        frictionEquationStiffness: data.frictionEquationStiffness,
        frictionEquationRegularization: data.frictionEquationRegularization
      });
    }
docs: Initializes the physics system.