/*
 * fsct.java - revised 17 Apr 05 - width 401, height 301
 * Rutherford scattering from a fixed force center for impact parameters
 *   less than five times distance of closest approach at head-on impact
 * SEQ - 26 particles at regular impact parameter increments
 * RND - 26 particles randomly distributed across the area of the beam
 * CNT - angular distribution for 500 randomly distributed particles
 * @author jackord@kw.igs.net
 */

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

public class fsct extends Applet 
                  implements ActionListener, Runnable {
  int kk=0; int first=0; double pi=Math.PI;            // Declarations
  String b1s="SEQ"; Button b1=new Button(b1s);
  String b2s="RND"; Button b2=new Button(b2s);
  String b3s="CNT"; Button b3=new Button(b3s);
  Thread tmr;
  int [] xx=new int[81];
  int [] yy=new int[81];

  public void init() {
    setBackground(new Color(211, 211, 211));
    add(b1); add(b2); add(b3);
    b1.addActionListener(this);
    b2.addActionListener(this);
    b3.addActionListener(this);
  }

  double hit(double y, Graphics g) {                   // Feynman Algorithm
    int phase, x1, y1, x2, y2;                         //   with trajectory
    double x, vx, vy, dt, r3;
    x=-200; dt=1; vx=.4416; vy=0; x1=0; y1=0;
    r3=Math.pow((x-200)*(x-200)+(y-150)*(y-150), 1.5);
    vx=vx+(x-200)/r3*dt/2; vy=vy+(y-150)/r3*dt/2;
    phase=1; 
    do {
      x=x+vx*dt; y=y+vy*dt;
      r3=Math.pow((x-200)*(x-200)+(y-150)*(y-150), 1.5);
      vx=vx+(x-200)/r3*dt; vy=vy+(y-150)/r3*dt;
      if (phase==2) {
        x2=(int)(x+.5); y2=(int)(y+.5);
        g.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
        if ((x2>400)||(y2>300)) {
          phase=3;
        }
      }
      if ((phase==1)&&(x>=0)) {
        x1=(int)(x+.5); y1=(int)(y+.5); phase=2;
      }
    } while ((phase<3)&&(r3<66000000));
    return Math.atan2(vy, vx)/pi*180;
  }

  double ctr(double y) {                               // Feynman Algorithm
    double x, vx, vy, dt, r3;                          //   no trajectory
    x=-200; dt=1; vx=.4416; vy=0;
    r3=Math.pow((x-200)*(x-200)+(y-150)*(y-150), 1.5);
    vx=vx+(x-200)/r3*dt/2; vy=vy+(y-150)/r3*dt/2;
    do {
      x=x+vx*dt; y=y+vy*dt;
      r3=Math.pow((x-200)*(x-200)+(y-150)*(y-150), 1.5);
      vx=vx+(x-200)/r3*dt; vy=vy+(y-150)/r3*dt;
    } while (r3<66000000);
    return Math.abs(Math.atan2(vy, vx)/pi*180);
  }


  double rnd() {                                       // Random impact
    double x, y, r;                                    //   parameter
    int test=0;
    do {
      x=Math.random(); y=Math.random();
      r=Math.pow((x-.5)*(x-.5)+(y-.5)*(y-.5), .5);
      if (r<=.5) { test=1; }
    } while (test==0);
    r=50*r;
    if (y<.5) { r=-r; }
    return 150+r;
  }
  public void start() {
    if (tmr==null) {
      tmr=new Thread(this);
      tmr.setPriority(Thread.MIN_PRIORITY);
      tmr.start();
    }
  }

  public void stop() {
    tmr=null;
  }

  public void run() {
    repaint();
  }

  public void paint(Graphics g) {                      // Paint
    double t, u; double z=125;
    int x1, y1, x2, y2, xorg, yorg;
    int [] cc=new int[20];
    xorg=30; yorg=280;
    if (first==0) {
      t=2*Math.atan(.2)/pi*180;
      xx[0]=xorg+(int)(2*t+.5); xx[1]=xx[0];
      yy[0]=yorg;
      yy[1]=20;
      for (int i=2; i<=80; i=i+1) {
        xx[i]=xorg+40+4*i;
        u=Math.tan(pi/180*(10+i));
        yy[i]=yorg-(int)(10*pi/9*(1+u*u)/u/u/u+.5);
        if (yy[i]<20) { yy[i]=20; }
      }
    }
    if (kk<3) {                                        // Scattering center
      g.setColor(Color.black); g.drawRect(0, 0, 400, 300);
      g.setColor(Color.green);
      g.fillArc(190, 140, 21, 21, 0, 360);
      g.drawArc(190, 140, 20, 20, 0, 360);
      g.setColor(Color.blue);
      if (kk==1) {                                     // Stepped impact
        while (z<176) {                                //   parameter
          hit(z, g);
          z=z+2;
        }
      }
      if (kk==2) {                                     // Random distribution
        for (int i=0; i<=25; i=i+1) {
          hit(rnd(), g);
        }
      }
    }
    if (kk==3) {                                       // 500 particle counter
      g.setColor(Color.blue);
      g.fillPolygon(xx, yy, 81);
      g.setFont(new Font("TimesRoman", Font.PLAIN, 14));
      g.drawString("N(<60) = 440", xorg+20, yorg+17);  // N with theta<60 deg
      g.drawString("N(>60) = 60", xorg+265, yorg+17);  // N with theta>60 deg 
      g.setColor(Color.black);
      for (int i=30; i<=390; i=i+20) {
        g.drawLine(i, 20, i, yorg);
      }
      for (int i=20; i<=280; i=i+20) {
        g.drawLine(xorg, i, 390, i);
      }
      g.drawString("0", xorg-3, yorg+17);
      g.drawString("60", 150-6, yorg+17);
      g.drawString("120", 270-9, yorg+17);
      g.drawString("180", 390-9, yorg+17);
      g.drawString("Theta  deg", 180, yorg+17);
      g.drawString("Cnt", 0, 136);
      g.drawString("0", xorg-12, yorg+6);
      g.drawString("100", xorg-24, yorg+6-100);
      g.drawString("200", xorg-24, yorg+6-200);
      try {                                            // Freeze display 2 sec
        Thread.sleep(2000);
      }
      catch (InterruptedException e) {
        stop();
      }
      g.setColor(Color.red);
      for (int i=1; i<=500; i=i+1) {
        x1=(int)(ctr(rnd())/10); cc[x1]=cc[x1]+1; x2=xorg+20*x1;
        y2=yorg-cc[x1]; g.drawLine(x2, y2, x2+20, y2);
      }
      x1=0; x2=0;
      for (int i=2; i<=5; i=i+1) {
        x1=x1+cc[i];
      }
      for (int i=6; i<=17; i=i+1) {
        x2=x2+cc[i];
      }
      g.clearRect(50, 281, 80, 18); g.clearRect(290, 281, 80, 18);
      g.drawString("N(<60) = "+x1, xorg+20, yorg+17);  // N with theta<60 deg
      g.drawString("N(>60) = "+x2, xorg+265, yorg+17); // N with theta>60 deg 
    }
    kk=0; stop();
  }

  public void actionPerformed(ActionEvent e) {         // Action Buttons
    String tst;
    tst=e.getActionCommand();
    if (b1s.equals(tst)) { kk=1; }
    if (b2s.equals(tst)) { kk=2; }
    if (b3s.equals(tst)) { kk=3; }
    start();
  }
}