/* * Mass.java *  * Created on 26/10/2007 *  * To change this template, choose Tools | Templates * and open the template in the editor. */package demos.nehe.lesson40;/** * Java implementation of Erkin Tunca's "Mass" class from "Physics1.h" by Scott Rains.<br/> * Date: 26 Oct 2007 * * @author Scott Rains (sid.rains[at]gmail.com) */public class Mass {    float m;                                    // The mass value    Vector3D pos;                                // Position in space    Vector3D vel;                                // Velocity    Vector3D force;                                // Force applied on this mass at an instance    /**     * Default constructor. Zeroed inital values for position, velocity and force.     *     * @param m Initial mass     */    public Mass(float m) {                            // Constructor        this.m = m;        pos = new Vector3D();        vel = new Vector3D();        force = new Vector3D();    }    /**     * void applyForce(Vector3D force) method is used to add external force to the mass.     * At an instance in time, several sources of force might affect the mass. The vector sum     * of these forces make up the net force applied to the mass at the instance.     * *param force Force vector to apply     */    public void applyForce(Vector3D force) {        this.force.addTo(force);                                                // The external force is added to the force of the mass    }    /**     * void init() method sets the force values to zero     */    public void init() {        force.x = 0;        force.y = 0;        force.z = 0;    }    /**     * void simulate(float dt) method calculates the new velocity and new position of     * the mass according to change in time (dt). Here, a simulation method called     * "The Euler Method" is used. The Euler Method is not always accurate, but it is     * simple. It is suitable for most of physical simulations that we know in common     * computer and video games.     * *param dt Delta time     */    public void simulate(float dt) {        vel.addTo(force.divide(m).multiply(dt));                // Change in velocity is added to the velocity.        // The change is proportinal with the acceleration (forceScaled / m) and change in time        pos.addTo(vel.multiply(dt));                        // Change in position is added to the position.        // Change in position is velocity times the change in time    }}