/*
 * h1b.java - revised 18 Ap5 05 - width 301, height 241
 * hanging chain (n mass points on an n+1 segment string)
 *   chain length = 400, n=64
 *   support separation: horizontal 240, vertical 120
 * the string tension and angle at the left support are varied
 *   to bring the end of the string to the right support
 * the analytic curve is a catenary (with integer constants)
 * @author jackord@kw.igs.net
 */

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

public class h1b extends Applet 
                  implements ActionListener {
  int n, phi; int kk=0; int show=1; int first=0;       // Declarations
  double tns, d;
  String b1s="Vary"; Button b1=new Button(b1s);
  TextField tx=new TextField(10);
  Image bim; Graphics bgr;

  public void init() {
    add(b1); add(tx);
    b1.addActionListener(this);
    setBackground(new Color(211, 211, 211));
    tx.setBackground(getBackground());
  }

  double hit(Graphics g) {                             // Trace out string
    int x1, y1, x2, y2;
    double x, y, q, t, tn, tc;
    x=10; y=10; q=phi*Math.PI/18000; t=tns;            // First angle & tension
    tn=Math.tan(q); tc=t*Math.cos(q);
    x=x+d*Math.cos(q); y=y-d*Math.sin(q); x1=(int)(x); y1=(int)(y);
    if (show==1) { g.drawLine(10, 10, x1, y1);}
    for (int i=1; i<=n; i=i+1) {                       // Loop
      tn=tn+1/tc; q=Math.atan(tn); t=tc/Math.cos(q);   // Next angle & tension
      x=x+d*Math.cos(q); y=y-d*Math.sin(q);
      x2=(int)(x); y2=(int)(y);
      if (show==1) { g.drawLine(x1, y1, x2, y2); x1=x2; y1=y2; }
    }
    return Math.sqrt((x-250)*(x-250)+(y-130)*(y-130)); // Return deviation
  }

  double ang(Graphics g) {                             // Find optimum angle
    double s, so; int dph=-256;
    show=0; s=hit(g);
    do {
      phi=phi+dph; so=s; s=hit(g);
      if (s>so) { dph=-dph/2; }
    } while (Math.abs(dph)>1);
    phi=phi+2*dph; show=1; s=hit(g);
    return s;
  }

  double cosh(double x) {                              // Cosh(x)
    return (Math.exp(x)+Math.exp(-x))/2;
  }

  double sinh(double x) {                              // Sinh(x)
    return (Math.exp(x)-Math.exp(-x))/2;
  }

  public void paint(Graphics g) {                      // Paint
    double dtns=2; double s, so, a, b, c, y;
    int y1=0; int y2, del;
    if (first==0) {
      bim=createImage(301, 241); bgr=bim.getGraphics();
      first=1;
    }
    bgr.setColor(Color.black); bgr.drawRect(0, 0, 300, 240);
    bgr.setColor(Color.red);
    bgr.fillArc(5, 5, 11, 11, 0, 360);
    bgr.drawArc(5, 5, 10, 10, 0, 360);
    bgr.fillArc(245, 125, 11, 11, 0, 360);
    bgr.drawArc(245, 125, 10, 10, 0, 360);
    if (kk==1) {
      a=152; c=69; b=27-c;                             // Catenary constants
      y=c*(sinh((250-a)/c)-sinh((10-a)/c));            // Catenary length
      for (int i=10; i<=250; i=i+1) {                  // Plot catenary
        y=b+c*cosh((i-a)/c); y2=240-(int)(y);
        if (i>10) { bgr.drawLine(i-1, y1, i, y2); }
        y1=y2;
      }
    }
    g.drawImage(bim, 0, 0, null);
    n=64; d=400./(n+1); phi=-6000; tns=48;
    g.setColor(Color.blue); s=hit(g);
    tx.setText("Dev = "+.01*(int)(100*s));
    if (kk==1) {
      del=500; long tt=System.currentTimeMillis();     // Initialize timing
      do {                                             // Vary initial tension
        tt=tt+del;
        while (System.currentTimeMillis()<tt) { }
        g.drawImage(bim, 0, 0, null);
        tns=tns+dtns; so=s; s=ang(g);                  // ... and angle
        tx.setText("Dev = "+.01*(int)(100*s));
        if (s>so) { dtns=-dtns/2; }
      } while (s>.1);                                  // ... to reach support
    }
    kk=0;
  }

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