/*
 * h8a.java - 18 Sep 07 - width 361, height 281
 * @author jackord@kw.igs.net
 * distant sphere moving perpendicular to the viewing direction
 *   at relativistic speeds
 * the co-ord system has x positive to the right, y positive downward,
 *   and z positive going away from you
 * the sphere is transparent with gridlines in blue on the near
 *   hemisphere (z<=0), and in red on the far hemisphere (z>0)
 */

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

public class h8a extends Applet
                 implements ActionListener {
  double pi=Math.PI;
  String b1s="Plot"; Button b1=new Button(b1s);
  Choice ch=new Choice();

  public void init() {
    setLayout(new FlowLayout(FlowLayout.LEFT));
    setBackground(new Color(211, 211, 211));
    ch.setBackground(getBackground());
    ch.addItem("v/c=0.0"); ch.addItem("v/c=0.2"); ch.addItem("v/c=0.4");
    ch.addItem("v/c=0.6"); ch.addItem("v/c=0.8"); 
    add(ch); add(b1); b1.addActionListener(this);
    ch.select(0);
  }
 
  public void paint(Graphics g) {
    double be, ga, th, ph, r, rr, x, xp, y, z;
    int xo, yo, n, si, x1, y1, x2, y2;
    n=120; r=90.; xo=180; yo=130;
    si=ch.getSelectedIndex();                          // Get velocity
    be=0.2*si; ga=1./Math.sqrt(1-be*be);               // Beta and Gamma
    g.setColor(Color.black);
    g.drawRect(0, 0, 360, 280);
    g.setFont(new Font("Arial", Font.PLAIN, 16));
    g.drawString("Sphere Moving to the Right at v/c = 0."+2*si, 45, 260);
    for (int i=1; i<=17; i=i+1) {                      // Latitude grid
      th=10*i*pi/180; rr=r*Math.sin(th);
      x=r*Math.cos(th); y=rr; z=0;
      xp=x/ga-be*z;                                    // Find x co-ord
      x1=xo+(int)(xp); y1=yo+(int)(y);
      g.setColor(Color.red);
      for (int j=1; j<=n; j=j+1) {
        if (j==n/2) { g.setColor(Color.blue); }
        ph=3*j*pi/180;
        y=rr*Math.cos(ph); z=rr*Math.sin(ph);
        xp=x/ga-be*z;                                  // Find x co-ord
        x2=xo+(int)(xp); y2=yo+(int)(y);
        g.drawLine(x1, y1, x2, y2);
        x1=x2; y1=y2;
      }
    }
    g.setColor(Color.red);
    for (int i=1; i<=36; i=i+1) {                      // Longitude grid
      if (i==18) { g.setColor(Color.blue); }
      ph=10*i*pi/180;
      x=-r; y=0; z=0;
      xp=x/ga-be*z;                                    // Find x co-ord
      x1=xo+(int)(xp); y1=yo+(int)(y);
      for (int j=1; j<=n/2; j=j+1) {
        th=3*j*pi/180;
        x=-r*Math.cos(th);
        y=r*Math.sin(th)*Math.cos(ph);
        z=r*Math.sin(th)*Math.sin(ph);
        xp=x/ga-be*z;                                  // Find x co-ord
        x2=xo+(int)(xp); y2=yo+(int)(y);
        g.drawLine(x1, y1, x2, y2);
        x1=x2; y1=y2;
      }
    }
  } 

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