/*
 * fgun.java - revised 13 Oct Apr 05 - width 451, height 271
 * @author jackord@kw.igs.net
 * a version of fhomer.java modified to deal with the variation of density
 *   with elevation in the atmosphere
 * finds the initial velocity required to give 40 cm diameter iron sphere
 *   a horizontal range of 40 km if there is
 *     (a) no atmosphere
 *     (b) a constant density atmosphere
 *     (c) a variable density atmosphere
 */

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

public class fgun extends Applet 
                  implements ActionListener {
  int ntry, show, dens; int kk=0; int rr=0; int first=0; // Declarations
  double gr, vi, vo, phi, dphi, k, t, tt, h;
  String b1s="Range"; Button b1=new Button(b1s);
  String b2s="Motion"; Button b2=new Button(b2s);
  Image aim, bim;
  Graphics agr, bgr;

  public void init() {
    setLayout(new FlowLayout(FlowLayout.LEFT));
    add(b1); add(b2);
    b1.addActionListener(this); b2.addActionListener(this);
    setBackground(new Color(211, 211, 211));           // Light Gray Background
  }

  double hit(Graphics g) {                             // Feynman Algorithm
    double x, y, q, vx, vy, dvx, dvy, dt, u, ux, uy, cc, xx, yy, vxx, vyy;
    int x1, y1, x2, y2, xx1, yy1, xx2, yy2, r;
    dt=.1; t=0; x=0; y=0; q=phi*Math.PI/180;
    vx=vi*Math.cos(q); vy=vi*Math.sin(q);
    x1=0; y1=250; xx1=x1; yy1=y1; r=6;
    if (kk==1) {                                       // Find Range
      if (dens==0) {                                   // No Air Resistance
        vy=vy-gr*dt/2;
        do {
          t=t+dt; x=x+vx*dt; y=y+vy*dt;
          x2=(int)(x/100); y2=(int)(250-y/100);
          g.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
          vy=vy-gr*dt;
        } while (y>0);
      }
      if (dens>0) {                                    // Sea-Level or
        dvx=-k*vx*vi*dt; vx=vx+dvx/2;                  //   variable density
        dvy=-(gr+k*vy*vi)*dt; vy=vy+dvy/2;             //   of air...
        do {
          t=t+dt; x=x+vx*dt; y=y+vy*dt;
          if (show==1) {
            x2=(int)(x/100); y2=(int)(250-y/100);
            g.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
          }
          ux=vx+dvx/2; uy=vy+dvy/2; u=Math.sqrt(ux*ux+uy*uy);
          if (dens==1) {                               // ...choose which
            cc=1;
          }
          else {
            cc=Math.exp(-y/h);
          }
          dvx=-cc*k*ux*u*dt; vx=vx+dvx;                // Newton's Law
          dvy=-(gr+cc*k*uy*u)*dt; vy=vy+dvy;
        } while (y>0);
      }
    }
    if (kk==2) {                                       // Plot Motion
      xx=0; yy=0; vxx=vo*Math.cos(Math.PI/4); vyy=vxx; tt=2*vyy/gr;
      dvx=-k*vx*vi*dt; vx=vx+dvx/2;                    
      dvy=-(gr+k*vy*vi)*dt; vy=vy+dvy/2;               
      do {
        t=t+dt; x=x+vx*dt; y=y+vy*dt;                  // With air
        if (y<0) {
          x=x-vx*y/vy; y=0;
        }
        xx=vxx*t; yy=vyy*t-gr*t*t/2;                   // Without air
        x2=(int)(x/100); y2=(int)(250-y/100);
        xx2=(int)(xx/100); yy2=(int)(250-yy/100);
        bgr.drawLine(x1, y1, x2, y2); x1=x2; y1=y2;
        if (yy>=0) {
          bgr.drawLine(xx1, yy1, xx2, yy2); xx1=xx2; yy1=yy2;
        }
        agr.drawImage(bim, 0, 0, null);
        agr.fillArc(x2-r, y2-r, 2*r, 2*r, 0, 360);     // Show...
        agr.fillArc(xx1-r, yy1-r, 2*r, 2*r, 0, 360);   // ...cannonballs
        g.drawImage(aim, 0, 0, null);
        cc=Math.exp(-y/h);                             // Newton's Law
        ux=vx+dvx/2; uy=vy+dvy/2; u=Math.sqrt(ux*ux+uy*uy);
        dvx=-cc*k*ux*u*dt; vx=vx+dvx;
        dvy=-(gr+cc*k*uy*u)*dt; vy=vy+dvy;
      } while (y>0);
    }
    return x;
  }

  double ang(Graphics g) {                             // Find Optimum Angle
    double dph, x, xo;
    dph=dphi; x=hit(g);
    do {
      phi=phi+dph; xo=x; x=hit(g);
      if (x<xo) { dph=-dph/2; }
    } while (Math.abs(dph)>.02);
    phi=phi+2*dph; ntry=ntry+1;
    if (ntry<5) {
      show=1; x=hit(g); show=0;
    }
    return xo;
  }

  public void paint(Graphics g) {                      // Main Program
    if (first==0) {
      aim=createImage(451, 271);                         // Animation buffers
      agr=aim.getGraphics();
      bim=createImage(451, 271);                     
      bgr=bim.getGraphics();
      first=1;
    }
    agr.setColor(Color.red);
    bgr.setColor(Color.black);
    for (int i=0; i<=450; i=i+50) {
      bgr.drawLine(i, 0, i, 250);
    }
    for (int i=0; i<=250; i=i+50) {
      bgr.drawLine(0, i, 450, i);
    }
    bgr.setColor(Color.blue);
    g.drawImage(bim, 0, 0, null);
    g.setColor(Color.black);
    g.setFont(new Font("TimesRoman", Font.PLAIN, 14));
    double m, r, va, vb, dvi, range;
    r=.2; m=4*Math.PI/3*7870*Math.pow(r, 3);
    gr=9.8; k=.87*r*r/m;
    range=40000; h=100000/9.8/1.21; vo=Math.sqrt(gr*range);
    if (kk==1) {                                       // Find the Range
      dens=0; vi=vo; phi=45;                           // No Air Resistance
      g.setColor(Color.red); hit(g);
      g.drawString((int)vi+" m/s at 45 deg", 20, 265);
      g.setColor(Color.yellow);
      for (int j=1; j<=2; j=j+1) {                     // Air Resistance
        ntry=0; show=0; dens=j;
        dvi=vo; vi=0; phi=45; dphi=2;
        do {                                           // Bracket the Range
          vi=vi+dvi;
        } while (ang(g)<range);
        va=vi-dvi; vb=vi;
        do {                                           // Bisection Algorithm
          vi=(va+vb)/2;
          if (ang(g)>range) {
            vb=vi;
          }
          else {
            va=vi;
          }
        } while (vb-va>.1);
        if (j==1) {
          g.setColor(Color.magenta);
        }
        else {
          g.setColor(Color.blue);
        }
        vi=(va+vb)/2; show=1; hit(g);
        g.drawString((int)vi+" m/s at "+(int)(10*phi+.5)/10.+" deg", 150*j, 265);
        g.setColor(Color.green);
      }
      kk=0; rr=1;
    }
    if (kk==2) {                                       // Plot the Motion
      hit(g);
      g.setColor(Color.blue);
      g.drawString("T = "+(int)tt+" sec without air", 50, 265);
      g.drawString("T = "+(int)t+" sec with air", 250, 265);
      kk=0;
    }
  }

  public void actionPerformed(ActionEvent e) {         // Buttons
    String tst;
    tst=e.getActionCommand();
    if (b1s.equals(tst)) {                             // Find the Range
      kk=1; repaint();
    }
    if ((b2s.equals(tst))&&(rr==1)) {                  // Plot the Motion
      kk=2; repaint();
    }
  }
}