import java.awt.*;
  import java.applet.*;
  import java.awt.image.*;
  /*Author Manuel J Paez
    Departamento de Fisica
    Universidad de Antioquia
    Medellin-COLOMBIA*/

public class Dinam extends Applet {
  private Scrollbar Bvelocity,Clockrate;
  private Dinamcan canv;
  private Panel elpanel,pan;
  private Button stp,rest;
  private TextField t1,t2,t3;

  public void init()
  {
     canv=new Dinamcan();
     canv.resize(520,380);
     pan=new Panel();
     elpanel=new Panel();
     stp=new Button("Stop");

     rest=new Button("Start");
     t1=new TextField("Vel B 0.8 c");
     t2=new TextField("v=0.5 c");
     t3=new TextField("rate=1.0");
     t1.setEditable(false);
     t2.setEditable(false);
     t3.setEditable(false);
     Bvelocity=new Scrollbar(Scrollbar.HORIZONTAL,80,0,10,99);
     Clockrate=new Scrollbar(Scrollbar.VERTICAL,40,0,10,110);
     elpanel.setLayout(new BorderLayout());
     pan.setLayout(new  GridLayout(10,1));

     pan.add(stp);
     pan.add(rest);
     pan.add(t1);
     pan.add(t2);
     pan.add(t3);
     elpanel.add("East", pan);
     elpanel.add("Center", canv);
     elpanel.add("South",Bvelocity);
     elpanel.add("West",Clockrate);
     setLayout(new BorderLayout());
     add("Center",elpanel);
     canv.Flag=0;
     canv.init();
     canv.start();
  }

 
    public boolean handleEvent(Event ev){
   //events sent by Dinamcan and scrollbar interpreted here
   if(ev.target instanceof Scrollbar){
     if(ev.target==Bvelocity){
        canv.xpos=(Bvelocity.getValue());
        t2.setText("v="+Double.toString(canv.vrel)+"c");
        t1.setText("Vel B "
       +Double.toString(canv.vwr)+"c");
     }
     if(ev.target==Clockrate){
       canv.tpos=(Clockrate.getValue());
       t3.setText("rate="+Double.toString(canv.trel));
     }
     canv.firstime=1;
     canv.jj=1;
     canv.scrollyes=1;
     canv.repaint();
     return true;
   }
     
    return super.handleEvent(ev);
  }

    public boolean action(Event ev, Object whataction)
    {
     if(ev.target instanceof Button){
       String buttonLabel=(String) whataction;

       if(buttonLabel=="Start"){
         canv.firstime=0;
         canv.jj=1; //To start from initial conditions
         canv.setFlag(1);
         canv.negat=1;
         canv.y0=110.0;
         canv.yb=1.0;
         canv.time2=0.0;
         canv.time3=0.0;
         canv.time4=0.0;
         canv.negat1=1;
         canv.scrollyes=1;
         return true;
       }
       if(buttonLabel=="Stop")
       {
         canv.setFlag(0);
         canv.firstime=1;
         return true;
       }
       return false;
      }//if button
      else
        if(ev.target instanceof Scrollbar){
        canv.postEvent(ev);//sent to Eqstring handlEvent
        return true;
      }
       return false;
     }
}//class

class Dinamcan extends Canvas  implements Runnable{
  public int xpos,tpos;
  Thread runstring;
  double mxx,bxx,myy,byy;
  Image offScreenImage;
  Graphics offScreenGraphics;
  double y0,yb,time3,time2,time4,vc2,sqv,vwr,vrel,trel,ttpos;
  int firstime,negat,negat1,bslx,bsly,Bslx,Bsly,alx,aly,Aly;
  int brsx,brsy,Brsx,Brsy,arx,ary,Arx,Ary;
  int jj;
  int Flag;
  int scrollyes;

  public void init(){
    jj=1;
    y0=110.0;
    yb=1.0;
    time2=0.0;
    time3=0.0;
    time4=0.0;
    xpos=80;
    tpos=40;
    negat=1;
    negat1=1;
    firstime=1;
    vc2=0.0;
    sqv=0.0;
    Flag=1;
    scrollyes=0;
    bslx=0;
    bsly=0;//initialize
    Bslx=0;
    Bsly=0;//initialize
    alx=0;
    aly=0;
    Aly=0;
    brsx=0;
    brsy=0;
    Brsx=0;
    Brsy=0;
    arx=0;
    ary=0;
    Arx=0;
    Ary=0;
    offScreenImage=createImage(size().width,size().height);
    trel=1.0;
  
  }
  public void start()
  {
   if(runstring==null)
   {
       runstring=new Thread(this);
       runstring.start();
    }
  }
  public void stop()
  { //stops motion

     if(runstring != null){
       runstring.suspend();
       runstring=null;

     }
  }
  public void run()
  {
    while(true){
       if(firstime==0) repaint();
      try{ Thread.sleep(15);
      }
      catch(InterruptedException e){ }
    }
  }
   public void setFlag(int fl)
  {
     Flag=fl;    //Flag 0 do not begin string motion, 1 yes
  }
  
  public void update(Graphics g)
  { //To avoid flicker
    Graphics offScreenGraphics=offScreenImage.getGraphics();
    offScreenGraphics.setColor(getBackground());
    offScreenGraphics.fillRect(0,0,size().width,size().height);
    offScreenGraphics.setColor(g.getColor());
    paint(offScreenGraphics);
    g.drawImage(offScreenImage,0,0,this);
  }

  void coormundo(double xiz,double ysu,double xde,double yinf)
  {
    double maxx,maxy,xxfin,xxcom,yyin,yysu;
    maxx=280;
    maxy=250;
    xxcom=maxx/12.0+100;
    xxfin=11.0*maxx/12.0+100;
    yyin=0.8*maxy;
    yysu=0.2*maxy;
    mxx=(xxfin-xxcom)/(xde-xiz);
    bxx=0.5*(xxcom+xxfin-mxx*(xiz+xde));
    myy=(yyin-yysu)/(yinf-ysu);
    byy=0.5*(yysu+yyin-myy*(yinf+ysu));
  }

  void ejes(double xmz,double yms,double xmd,double ymi,int
  offy,Graphics g, int tics)
  {
    //Plot the axis
    //  0.0 to 1.0
    int mp,xpi,xpd,yps,ypi,xdvi,ypcen,i;
    char nver;
    int sig=4;
    mp=(int)((xmd-xmz)/tics);
    xpi=(int)(mxx*xmz+bxx);
    xpd=(int)(mxx*xmd+bxx);
    yps=(int)(myy*yms+byy);
    ypi=(int)(myy*ymi+byy);
    ypcen=(int)byy;
    g.drawLine(xpi,ypcen-30+offy,xpd,ypcen-30+offy);
    g.drawLine(xpi,yps-30+offy,xpi,ypi-30+offy);
    xdvi=xpi;
    for(i=1;i<=mp;i++){
        xdvi=xdvi+tics;
      g.drawLine(xdvi,ypcen-40+offy,xdvi,ypcen-25+offy);
    }

  }
   void Arrow(Graphics g, int xsc, int ysc, int col){
      int arrow;
      if(col==1)g.setColor(Color.black);
      if(col==0)g.setColor(getBackground());
      arrow=(int)(40.0*xpos/50.0)+55;
      g.drawLine(xsc,ysc,arrow+xsc,ysc);//arrow
      g.drawLine(xsc+arrow-5,ysc+5,xsc+arrow,ysc); //upper tip
      g.drawLine(xsc+arrow-5,ysc-5,xsc+arrow,ysc); //lower tip
    }
  public void clock(Graphics g, double time, int xov,int yov)
  { //draws clock at given initial angle
    int r,xti,yti,xc,yc;
    float xpnt,ypnt;
    r=30;
    xpnt=(float)(0.5*r*Math.sin(3.141592*time/125.0));
    ypnt=(float)(0.5*r*Math.cos(3.141592*time/125.0));
    g.drawOval(xov,yov,r, r);
    xti=(int)xpnt;
    yti=(int)ypnt;
    xc=xov+15;
    yc=yov+15;
    g.drawLine(xc,yc,xc+xti,yc-yti);
  }


  public void Dinamplot(Graphics g)
  {
    double dx,dt,xx,xxb,vsi,uyb,xb,c,uxb;
    double uya,xa,ya,time,ybp,yap,xxpos,t0p,dtp,t0,yy0,xred;

    /* uya:lab vel part A y direc.
       uxb:lab vel part B x direc. is selected with scrollbar
       Uyb: rocket vel part B y direc.
       p: after collision, vertical
       vsi: relative velocity of one system w r t the other */

    double Uya,Xa,Xa0,Yap,Xb,Time,Ybp,Uyb,Yb,Ya;//red particles
    //upper case primed system
    double ty,xacom,tiempo,tco,xin,Ybini,Tcol;
    int j,col,wri,vreli,tics, ticsv,jump;
    int nmaxi,k,i;
    int peb,peyb,pea,peya,pex,Peb,Pea,Peya,Peyb,pexb;
    dt=1.0;
    vsi=1.0;         //vel of one system wrt the other
    tics=90;
    xxpos=(double)xpos;      //from scrollbar
    uyb=1.0;                 //y vel b particle in lab
    time=0.0;
    ybp=0.0;
    Xb=0.0;
    jump=1;
    tiempo=0.0;
    uya=1.0;
    Pea=0;
    Peya=0;
    Tcol=0.0; //initialize time of colision in S prime from origin
    Peb=0;
    c=2.5;                    //light speed
    uxb=xxpos*c/100.0;        //selected with scrollbar
    wri=(int)(1000.0*uxb/2.5);
    vwr=wri/1000.0;            //to write in screen
    ty=y0/uyb;            //time from y0 to x axis for b
    xa=uxb*ty;            //initial position of A (same distance b)
    Xa0=xa;
    vsi=c*c/uxb-c*Math.sqrt(c*c/(uxb*uxb)-1.0);// v=ubx'  //system v
    vreli=(int)(1000.0*vsi/c);//limit decimal places
    vrel=vreli/1000.0;
    vc2=vsi*vsi/c/c;
    sqv=Math.sqrt(1.0-vc2);
    ticsv=(int)(tics*sqv);
    Uyb=uyb*sqv/(1.0-uxb*vsi/c/c);
    Uya=uya*sqv;
    t0p=-xa*vsi/(c*c*sqv);
    t0=-t0p/sqv;         //positive at the beginning
    xin=-t0*vsi;
    dtp=0.0;
    xb=-uxb*t0;
    ya=-y0-uyb*t0;
    yb=y0+uyb*t0;
    Yb=y0+Uyb*t0; //t0p is -
    yy0=yb;
    Ybini=Yb;
    ttpos=(int)(((double)tpos*0.03-0.2)*1000.0); //scale 0.1 to 3.1
    trel=(double)ttpos/1000.0;
    tco=(2.0*y0)/(Uya+Uyb);//begins when the 2 systems coincide
    Tcol=(2.0*y0)/(Uya+Uyb);//begins when the 2 systems coincide
    xred=-vsi*t0;        //motion of red system
    Xb=-vsi*t0;//arrives a y prime when blue does
    xacom=vsi*t0+2*vsi*tco;//initial position A in S prime
    Xa=xacom;
    Ya=-y0-Uya*t0;
  
    if(jj==1){
      coormundo(0,220.0,800.0,-220.0);
      g.drawString("Laboratory system",15,100);
      g.drawString("Rocket system",310,300);
      peb=(int)(mxx*xb+bxx);
      Peb=(int)(mxx*Xb+bxx);
      Pea=(int)(mxx*Xa+bxx);
      peyb=(int)(myy*yb+byy-30);//-30
      peya=(int)(myy*ya+byy-30);//-30
      Peya=(int)(myy*Ya+byy-30);
      Peyb=(int)(myy*Yb+byy-30);
      pea=(int)(mxx*xa+bxx);
      Arrow(g,peb,peyb,1);
      g.setColor(Color.blue);
      clock(g,-t0, 35,35);
      bslx=peb;
      bsly=peyb;
      g.fillOval(peb-5,peyb-5,10,10);
      alx=pea;
      aly=peya;
      g.drawOval(pea-5,peya-5,10,10);
      g.drawString("A",pea-15, peya);
      g.drawString("B",160,30);
      ejes(0.0,220.0,800.0,-220.0,0,g,0);
      ejes(-xin,220.0,800.0-xin,-220.0,160,g,0);
      g.setColor(Color.red);
      clock(g,-t0,300,180);
      ejes(0,220.0,800.0,-220.0,160,g,0);
      ejes(xred,220.0,800.0,-220.0,0,g,0);
      brsx=Peb;
      brsy=Peyb;
      g.fillOval(Peb-5,Peyb-5+160,10,10);
      arx=Pea;
      ary=Peya;
      g.drawOval(Pea-5,Peya-5+160,10,10);
    }
    //loop over time
    for(k=1;k<jj+1;k++){
      if((k==jj)&&(k>1))
      {
        Tcol=t0+Tcol-dt*trel;
        if(Tcol<=0.0)time4=time4+1.0;
        pea=(int)(mxx*xa+bxx);
        g.drawString("Laboratory system",15,100);
        g.drawString("Rocket system",310,300);
        g.setColor(Color.red);
        ejes(0,220.0,800.0,-220.0,160,g,0);
        clock(g,-t0+trel*dt,300,180);              // x tprime red
        g.setColor(Color.blue);
        clock(g,-t0+dt, 35,35);
        ejes(0,220.0,800.0,-220.0,0,g,0);
        xx=vsi*dt;                               // red axis moving
        xxb=trel*vsi*dt;                         //blue axis move
        xb=xb+ uxb*dt;
        Xa=xacom-trel*vsi*dtp;                   //motion of A rocket
        peb=(int)(mxx*xb+bxx);

        Xb=-vsi*t0+trel*vsi*tiempo; //rocket B
        if(Tcol>=0.0){
          Yb=Ybini-Uyb*tiempo*trel; //rocket B
//          g.drawString("Tcol  "+Tcol/trel,100,70);
//         g.drawString("Tcol/terel  "+Tcol,100,40);
          Peb=(int)(mxx*Xb+bxx);
          Ya=-y0-Uya*t0+trel*Uya*dt;
          Pea=(int)(mxx*Xa+bxx);
          Peya=(int)(myy*Ya+byy-30);
          g.setColor(Color.red);
          Peyb=(int)(myy*Yb+byy-30);
          g.drawLine(brsx,brsy+160,Peb,Peyb+160);
          g.fillOval(Peb-5,Peyb-5+160,10,10);
          g.drawLine(arx,ary+160,Pea,Peya+160);
          g.drawOval(Pea-5,Peya-5+160,10,10);
          Brsx=Peb;
          Brsy=Peyb;
          Arx=Pea;
          Ary=Peya;
        }
        if(Tcol<=0.0)
        {

          g.setColor(Color.red);
          Ybp=y0+time4*Uyb*trel-tco*Uyb;//after colision  b part.
          Yap=-y0+Uya*tco-time4*Uya*trel;
          Peb=(int)(mxx*Xb+bxx);
          Peyb=(int)(myy*Ybp+byy-30);
          Pea=(int)(mxx*Xa+bxx);
          Peya=(int)(myy*Yap+byy-30);
          g.fillOval(Peb-5,Peyb-5+160,10,10);
          g.drawLine(Brsx,Brsy+160,Peb,Peyb+160);
          g.drawLine(brsx,brsy+160,Brsx,Brsy+160);
          g.drawOval(Pea-5,Peya-5+160,10,10);
          g.drawLine(Arx,Ary+160,Pea,Peya+160);
          g.drawLine(arx,ary+160,Arx,Ary+160);

        }
        g.setColor(Color.blue);
        if((yb>0.0)){
          yb=yy0-uyb*time;
          ya=-yy0+uya*time;
          peyb=(int)(myy*yb+byy-30);//-30
          Arrow(g,peb,peyb,0);
          peya=(int)(myy*ya+byy-30);//-30
          pex=(int)(mxx*xx+bxx);
          pexb=(int)(mxx*xxb+bxx);
          g.setColor(Color.red);
          ejes(xred+xx,220.0,800.0+xred+xx,-220.0,0,g,0);
          if(negat==1){
            g.setColor(Color.blue);
            g.drawLine(bslx,bsly,peb,peyb);
            g.fillOval(peb-5,peyb-5,10,10);
            g.drawLine(alx,aly,pea,peya);

            g.drawOval(pea-5,peya-5,10,10);
            Bslx=peb;
            Bsly=peyb;
            Aly=peya;
          }
          if(negat1==-1){
            time3=time3+1.0;
            g.setColor(Color.red);
          }
        }//yb>0.0

        if(yb<=0.0) negat=-1;

        g.setColor(Color.blue);
        ejes(-xred-xxb,220.0,800.0-xred-xxb,-220.0,160,g,0);
        if(yb<=0.0){
            g.setColor(Color.blue);
            ybp= uyb*time2;
            yap=-uya*time2;
            peyb=(int)(myy*ybp+byy-30);
            peya=(int)(myy*yap+byy-30);
            g.drawLine(Bslx,Bsly,peb,peyb);
            g.drawLine(bslx,bsly,Bslx,Bsly);
            g.fillOval(peb-5,peyb-5,10,10);
            g.drawLine(pea,Aly,pea,peya);
            g.drawOval(pea-5,peya-5,10,10);
            g.setColor(Color.red);
            time3=time3+1.0;
         }   //if yb
      }//if k
      dt=dt+1.0;
      time=time+1.0;
      if(yb<=0.0)time2=time2+1.0;
      dtp=dtp+1.0;
      tiempo=tiempo+1.0;
    } //for k
  } //rutine

  public void paint(Graphics g){
    int maxim;
    maxim=550;
    if(trel<0.5)maxim=1200;
    if(trel>1.5)maxim=300;
    Dinamplot(g);
    if((Flag==1)&&(scrollyes==1)){
      jj=jj+1;
    }
    if(jj==maxim){
     firstime=1;
    }
  }
}//class can