/*
 * kepler.java
 *
 * Created on 23. Mai 2004, 22:17
 */

/**
 *
 * @author  nus
 */

import java.awt.*;
import java.applet.*;
import java.awt.event.*;

public class kepler extends Applet implements ActionListener {

    TextField vein;
    TextField alphaein;
    TextField hein;
    TextField dtein;
    Button ok;
    double v;
    double alpha = 0;
    double h;
    double dt;
    
    public void init() {
        setLayout(new BorderLayout());
        Panel panel = new Panel();
        panel.setLayout(new GridLayout(12,1,10,5));
        Label text = new Label("Eingaben - ");
        panel.add(text);
        Label labelv = new Label("Startgeschwindigkei");
        panel.add(labelv);
        vein = new TextField("2000",8);
        panel.add(vein);
        Label labela = new Label("Startwinkel");
        panel.add(labela);
        alphaein = new TextField("0",8);
        panel.add(alphaein);
        Label labelh = new Label("Starthöhe");
        panel.add(labelh);
        hein = new TextField("10", 8);
        panel.add(hein);
        Label labelt = new Label("Zeitschritt");
        panel.add(labelt);
        dtein = new TextField("1000",8);
        panel.add(dtein);
        ok = new Button("ok");
        panel.add(ok);
        ok.addActionListener(this);
        
        add("East",  panel);
    }
    
    public void actionPerformed (ActionEvent ae) {
        if (ae.getSource() == ok) {
            werteuebernehmen();
            repaint();
        }
        
    }
    
    public void werteuebernehmen() {
        v = Double.valueOf(vein.getText()).doubleValue();
        alpha = Double.valueOf(alphaein.getText()).doubleValue();
        h = Double.valueOf(hein.getText()).doubleValue();
        dt = Double.valueOf(dtein.getText()).doubleValue();
    }
    
    public void paint(Graphics bs) {
        
        int zaehler=120;
        
        double GM = 392000000000000.0;
        double er = 6470000;
        double ax;
        double ay;
        double vx;
        double vy;
        double x;
        double y;
        double r;
        
        double r3;
        
        alpha = alpha/180 * 3.14;
        vx = v * Math.sin(alpha);
        vy = v * Math.cos(alpha);
        x = h * er;
        y = 0;
        
        Color yl = new Color(255,255,245);
        bs.setColor(yl);
        bs.fillRect(0,0, 600,600);
        
        bs.setColor(Color.red);
        bs.drawOval(200 - (int) (er/(20*er)*400),
                    200 - (int)(er/(20*er)*400),
                    (int)(er/(20*er)*800),
                    (int)(er/(20*er)*800));
        bs.setColor(Color.blue);
        
        for (int i=1; i < zaehler; i++) {
            r3 = Math.sqrt(x*x + y*y);
            r = r3*r3*r3;
            ax = -GM*x/r;
            ay = -GM*y/r;
            vx = vx + ax*dt;
            vy = vy + ay*dt;
            x = x + vx*dt;
            y = y + vy*dt;
            
            bs.fillRect(200 + (int)(x/(20*er)*400), 200+(int)(y/(20*er)*400), 2, 2);
        }
    }
    
}