/*
 * fglf.java - revised 8 Apr 05 - width 451, height 141
 * effect of wind on a golfball hit at 100 mph at a 37 degree elevation
 * (a) no wind, (b) 10 mph headwind, (c) 10 mph tailwind, (d) 10 mph crosswind
 * @author jackord@kw.igs.net
 */

import java.applet.Applet;
import java.awt.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class fglf extends Applet 
                  implements ActionListener {
  int kk=0; double tf, xf, ax, ay;                     // Global variables
  String b1s="Wind"; Button b1=new Button(b1s);

  public void init() {
    setBackground(new Color(211, 211, 211));           // Light Gray Background
    add(b1); b1.addActionListener(this);
  }

  public void hit(double vx, double vy) {              // Hit the ball
    double x, y, dvx, dvy, t, dt;
    t=0; x=0; y=0; dt=.01;
    acc(vx, vy); dvx=ax*dt; dvy=ay*dt; vx=vx+dvx/2; vy=vy+dvy/2;
    do {                                               // Feynman loop
      t=t+dt; x=x+vx*dt; y=y+vy*dt;
      acc(vx+dvx/2, vy+dvy/2);
      dvx=ax*dt; dvy=ay*dt; vx=vx+dvx; vy=vy+dvy;
    } while (y>0);
    xf=x-vx*y/vy; tf=t-y/vy;                           // Return xf, tf
  }

  public void acc(double ux, double uy) {              // Newton's Law
    double u; double gr=9.8; double vt=33.7;
    u = Math.sqrt(ux*ux+uy*uy)*gr/vt/vt;
    ax=-u*ux; ay=-u*uy-gr;
  }

  public void paint(Graphics g) {                      // Paint
    double vb=44.7; double vw=4.47;
    double v; int x1, y1;
    g.drawRect(0, 0, 450, 140); g.drawLine(10, 70, 440, 70);
    hit(.8*vb, .6*vb);                                 // No wind
    x1=8+(int)(4*xf+.5);
    g.drawString("xf="+xf+"  tf="+tf, 40, 40);
    g.setColor(Color.green);
    g.fillArc(x1-60, 70-60, 120, 120, 0, 360);
    g.setColor(Color.red);
    g.fillArc(x1-5, 70-5, 10, 10, 0, 360);
    g.fillArc(8-5, 70-5, 10, 10, 0, 360);
    if (kk==1) {
      hit(.8*vb+vw, .6*vb);                            // Headwind
      x1=8+(int)(4*(xf-vw*tf)+.5);
      g.fillArc(x1-5, 70-5, 10, 10, 0, 360);
      g.drawString("xf="+(xf-vw*tf)+"  tf="+tf, 40, 60);
      hit(.8*vb-vw, .6*vb);                            // Tailwind
      x1=8+(int)(4*(xf+vw*tf)+.5);
      g.fillArc(x1-5, 70-5, 10, 10, 0, 360);
      g.drawString("xf="+(xf+vw*tf)+"  tf="+tf, 40, 80);
      v=Math.sqrt(.64*vb*vb+vw*vw);                    // Crosswind
      hit(v, .6*vb);
      x1=8+(int)(4*(xf*.8*vb/v)+.5); y1=(int)(4*(vw*tf-xf*vw/v)+.5);
      g.fillArc(x1-5, 70-y1-5, 10, 10, 0, 360);
      g.fillArc(x1-5, 70+y1-5, 10, 10, 0, 360);
    }
  }

  public void actionPerformed(ActionEvent e) {         // Button
    String tst;
    tst=e.getActionCommand();
    if (b1s.equals(tst)) { kk=1; repaint(); }
  }
}