java - Java 中的简单物理模拟不起作用。

Question

我想实现球物理，作为新手，我调整了教程中的代码 http://adam21.web.officelive.com/Documents/JavaPhysicsTutorial.pdf .

我尽我所能地遵循它，但是我不能在代码中应用所有的物理现象，有人可以告诉我，我错在哪里或者我还在做一些愚蠢的编程错误。

当我没有调用弹跳方法并且我无法使用弹跳方法时，球正在移动并且球正在向左侧移动而不是落在地板上**，

有人可以向我推荐一些更好的方法或类似的简单紧凑的方法来完成将物理应用于两个或多个具有交互性的球的任务吗。

这是代码；

    import java.awt.*;
    public class AdobeBall {

    protected int radius = 20;
    protected Color color;

    // ... Constants
    final static int DIAMETER = 40;

    // ... Instance variables
    private int m_x; // x and y coordinates upper left
    private int m_y;

    private double dx = 3.0; // delta x and y 
    private double dy = 6.0;

    private double m_velocityX; // Pixels to move each time move() is called.
    private double m_velocityY;

    private int m_rightBound; // Maximum permissible x, y values.
    private int m_bottomBound;

    public AdobeBall(int x, int y, double velocityX, double velocityY,
            Color color1) {
        super();
        m_x = x;
        m_y = y;
        m_velocityX = velocityX;
        m_velocityY = velocityY;
        color = color1;
    }

    public double getSpeed() {
        return Math.sqrt((m_x + m_velocityX - m_x) * (m_x + m_velocityX - m_x)
                + (m_y + m_velocityY - m_y) * (m_y + m_velocityY - m_y));
    }

    public void setSpeed(double speed) {
        double currentSpeed = Math.sqrt(dx * dx + dy * dy);
        dx = dx * speed / currentSpeed;
        dy = dy * speed / currentSpeed;
    }

    public void setDirection(double direction) {
        m_velocityX = (int) (Math.cos(direction) * getSpeed());
        m_velocityY = (int) (Math.sin(direction) * getSpeed());
    }

    public double getDirection() {
        double h = ((m_x + dx - m_x) * (m_x + dx - m_x))
                + ((m_y + dy - m_y) * (m_y + dy - m_y));
        double a = (m_x + dx - m_x) / h;
        return a;
    }

    // ======================================================== setBounds
    public void setBounds(int width, int height)  {
        m_rightBound = width - DIAMETER;
        m_bottomBound = height - DIAMETER;
    }

    // ============================================================== move
    public void move()  {

        double gravAmount = 0.02;
        double gravDir = 90; // The direction for the gravity to be in.
        // ... Move the ball at the give velocity.
        m_x += m_velocityX;
        m_y += m_velocityY;

//       ... Bounce the ball off the walls if necessary.
        if (m_x < 0) { // If at or beyond left side
            m_x = 0; // Place against edge and
            m_velocityX = -m_velocityX;

        } else if (m_x > m_rightBound) { // If at or beyond right side
            m_x = m_rightBound; // Place against right edge.
            m_velocityX = -m_velocityX;
        }

        if (m_y < 0) { // if we're at top
            m_y = 0;
            m_velocityY = -m_velocityY;

        } else if (m_y > m_bottomBound) { // if we're at bottom
            m_y = m_bottomBound;
            m_velocityY = -m_velocityY;
        }

     //   double speed = Math.sqrt((m_velocityX * m_velocityX)
     //         + (m_velocityY * m_velocityY));

        // ...Friction stuff 
        double fricMax = 0.02; // You can use any number, preferably less than 1
        double friction = getSpeed();
        if (friction > fricMax)
            friction = fricMax;
        if (m_velocityX >= 0) {
            m_velocityX -= friction;
        }
        if (m_velocityX <= 0) {
            m_velocityX += friction;
        }
        if (m_velocityY >= 0) {
            m_velocityY -= friction;
        }
        if (m_velocityY <= 0) {
            m_velocityY += friction;
        }

        // ...Gravity stuff

        m_velocityX += Math.cos(gravDir) * gravAmount;
        m_velocityY += Math.sin(gravDir) * gravAmount;

    }

    public Color getColor() {
        return color;
    }

    public void setColor(Color newColor)  {
        color = newColor;
    }

    // ============================================= getDiameter, getX, getY
    public int getDiameter() {
        return DIAMETER;
    }

  public double getRadius() {
        return radius; // radius should be a local variable in Ball.
    }

    public int getX() {
        return m_x;
    }

    public int getY() {
        return m_y;
    }

}

使用 adobeBall:

    import java.awt.*;
    import java.awt.event.*;
    import javax.swing.*;

    public class AdobeBallImplementation implements Runnable {

    private static final long serialVersionUID = 1L;

    private volatile boolean Play;
    private long mFrameDelay;
    private JFrame frame;
    private MyKeyListener pit;

    /** true means mouse was pressed in ball and still in panel. */
    private boolean _canDrag = false;

    private static final int MAX_BALLS = 50; // max number allowed
    private int currentNumBalls = 2; // number currently active
    private AdobeBall[] ball = new AdobeBall[MAX_BALLS];

    public AdobeBallImplementation(Color ballColor) {

        frame = new JFrame("simple gaming loop in java");
        frame.setSize(400, 400);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        pit = new MyKeyListener();
        pit.setPreferredSize(new Dimension(400, 400));
        frame.setContentPane(pit);

        ball[0] = new AdobeBall(34, 150, 7, 2, Color.YELLOW);
        ball[1] = new AdobeBall(50, 50, 5, 3, Color.BLUE);
        frame.pack();
        frame.setVisible(true);
        frame.setBackground(Color.white);
        start();
        frame.addMouseListener(pit);
        frame.addMouseMotionListener(pit);

    }

    public void start() {
        Play = true;
        Thread t = new Thread(this);
        t.start();
    }

    public void stop() {
        Play = false;
    }

    public void run() {

        while (Play == true) {
            // bounce(ball[0],ball[1]);
            runball();
            pit.repaint();
            try {
                Thread.sleep(mFrameDelay);
            } catch (InterruptedException ie) {
                stop();
            }
        }
    }

    public void drawworld(Graphics g) {

        for (int i = 0; i < currentNumBalls; i++) {
            g.setColor(ball[i].getColor());
            g.fillOval(ball[i].getX(), ball[i].getY(), 40, 40);
        }
    }

    public double pointDistance (double x1, double y1, double x2, double y2) {
        return Math.sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1));
    }

    public void runball() {

        while (Play == true) {
            try {

                for (int i = 0; i < currentNumBalls; i++) {
                    for (int j = 0; j < currentNumBalls; j++) {

                        if (pointDistance(ball[i].getX(), ball[i].getY(),
                                ball[j].getX(), ball[j].getY()) < ball[i]
                                                                       .getRadius()
                                                                       + ball[j].getRadius() + 2) {
                            // bounce(ball[i],ball[j]);
                            ball[i].setBounds(pit.getWidth(), pit.getHeight());
                            ball[i].move();

                            pit.repaint();

                        }
                    }
                }

                try {
                    Thread.sleep(50);
                } catch (Exception e) {
                    System.exit(0);
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    public static double pointDirection(int x1, int y1, int x2, int y2) {
        double H = Math.sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1)); // The
        // hypotenuse
        double x = x2 - x1; // The opposite
        double y = y2 - y1; // The adjacent
        double angle = Math.acos(x / H);
        angle = angle * 57.2960285258;
        if (y < 0) {
            angle = 360 - angle;
        }
        return angle;
    }

    public static void bounce(AdobeBall b1, AdobeBall b2) {
        if (b2.getSpeed() == 0 && b1.getSpeed() == 0) {
            // Both balls are stopped.
            b1.setDirection(pointDirection(b1.getX(), b1.getY(), b2.getX(), b2
                    .getY()));
            b2.setDirection(pointDirection(b2.getX(), b2.getY(), b1.getX(), b1
                    .getY()));
            b1.setSpeed(1);
            b2.setSpeed(1);
        } else if (b2.getSpeed() == 0 && b1.getSpeed() != 0) {
            // B1 is moving. B2 is stationary.
            double angle = pointDirection(b1.getX(), b1.getY(), b2.getX(), b2
                    .getY());
            b2.setSpeed(b1.getSpeed());
            b2.setDirection(angle);
            b1.setDirection(angle - 90);
        } else if (b1.getSpeed() == 0 && b2.getSpeed() != 0) {
            // B1 is moving. B2 is stationary.
            double angle = pointDirection(b2.getX(), b2.getY(), b1.getX(), b1
                    .getY());
            b1.setSpeed(b2.getSpeed());
            b1.setDirection(angle);
            b2.setDirection(angle - 90);
        } else {
            // Both balls are moving.
            AdobeBall tmp = b1;
            double angle = pointDirection(b2.getX(), b2.getY(), b1.getX(), b1
                    .getY());
            double origangle = b1.getDirection();
            b1.setDirection(angle + origangle);
            angle = pointDirection(tmp.getX(), tmp.getY(), b2.getX(), b2.getY());
            origangle = b2.getDirection();
            b2.setDirection(angle + origangle);
        }
    }

    public static void main(String[] args) {

        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new AdobeBallImplementation(Color.red);
            }
        });
    }

}   

*编辑:*确定使用来自该论坛的重力新方法拆分代码:此代码也不起作用球不会落在地板上:

public void mymove() {

    m_x += m_velocityX;
    m_y += m_velocityY;

    if (m_y + m_bottomBound > 400) {
        m_velocityY *= -0.981;
    //  setY(400 - m_bottomBound);
        m_y = 400 - m_bottomBound;

    }

    // ... Bounce the ball off the walls if necessary.
    if (m_x < 0) { // If at or beyond left side
        m_x = 0; // Place against edge and
        m_velocityX = -m_velocityX;

    } else if (m_x > m_rightBound) { // If at or beyond right side
        m_x = m_rightBound - 20; // Place against right edge.
        m_velocityX = -m_velocityX;
    }

    if (m_y < 0) { // if we're at top
        m_y = 1;
        m_velocityY = -m_velocityY;

    } else if (m_y > m_bottomBound) { // if we're at bottom
        m_y = m_bottomBound - 20;
        m_velocityY = -m_velocityY;

    }
}

非常感谢任何更正和帮助。

吉比

Answer 1

目前我无法运行 java，因此无法测试您的代码，但我注意到几件事:

1. 对于(几乎)同一件事，您有两组独立的变量:{dx, dy} 和 {m_velocityX, m_velocityY}。因此，您的 getSpeed 和 setSpeed 是独立的，getDirection 和 Setdirection 也是如此。我不敢相信这会按您期望的方式工作。
2. 你的坐标似乎有点困惑(这可能是球“落”到左边的原因)。您似乎是从 X 方向顺时针测量角度，这不符合标准。 编辑:Plínio Pantaleão 已经确定了向左跌落的原因。
3. 您的代码似乎涉及简单的线性运动、弹跳、重力和摩擦。您应该一次实现和测试这些。我建议先添加运动，然后添加弹跳，然后分别添加摩擦力和重力(以任意顺序)，最后将它们组合起来。

编辑:
这个重力代码是错误的:

if (m_y + m_bottomBound > 400) {
    m_velocityY *= -0.981;
    //  setY(400 - m_bottomBound);
    m_y = 400 - m_bottomBound;
}

首先，您将 400 用作“魔数(Magic Number)”；说不清代表什么。然后你将效果限制在屏幕顶部附近的区域，原因尚不清楚。在函数的末尾，您以一种毫无意义的方式更改了 m_y。并且(也许)最糟糕的是，重力反转并倍增垂直速度，这不是重力的工作原理。

试试这个:

// You will have to adjust this. Start with a small value and increase it until
// you see an effect.
final static double GRAVITY = 0.1;

// Note that +y is down, so accelerating downward means increasing vY
m_velocityY += GRAVITY;