//=======================file name : SolarSys===========
//      Simulation for a soler system 1.03 (JDK1.02)
//                KATO Noriyoshi 1997.3.23
//                    Sendai Miyagi Japan
//====================================================

import java.applet.*;
import java.awt.*;


public class SolarSys extends Applet implements Runnable
{
    Graphics g_this;
    Image offScreen;
    Graphics offGraphics;
    Dimension dim1;

    Thread th;
    
    Color col=new Color(75,85,135); 
       
  	//variables for Runge-Kutta
	double x[][]=new double[10][3];
	double v[][]=new double[10][3];
	double dx[][][]=new double[10][10][3];
	double nrm[][][]=new double[10][10][3];
	double pow[][]=new double[10][10];
	double ik[][][]=new double[4][10][3];
	double im[][][]=new double[4][10][3];
	double r[][]=new double[10][10];
	double aa[][]=new double[10][10];
	double al[][]=new double[10][10];
	int ap[][]=new int[10][10];
	double b[]=new double[10];
	double c[]=new double[10];
	double d[][]=new double[10][3];
	double x0[][]=new double[10][3];
	double mass[]=new double[10];
	double x1[][]=new double[10][3];
	double v1[][]=new double[10][3];
	double v2[][]=new double[10][3];
	double vn[][]=new double[10][3];
	double w[][]=new double[10][3];
	double w1[][]=new double[10][3];
	double va[]=new double[10];
	double f[][]=new double[10][3];
	double coef[]={1.,2.,2.,1.};
	
	//switch of forces
	boolean swa=true;
	boolean swb=true;
	boolean swc=true;
	boolean swd=true;

	int dim;//# of dimension -1
	int n;//# of body-1
	double dt;//time interval
	double time;//time

    int FONTSIZE1=12;
	int oldx[][]=new int[3][2];
	int oldnv[][]=new int[3][4];

    Point pt0=new Point(220,200);
    int drawmode=2;
    int drawinitflag=1;
    int stepflag=0;
	int drawvflag=1;
	int targetn=0; 
	int oldtargetn=0;   
    int dd[]={10,5,20};
    int DD=11;
    Color co[]={Color.cyan,Color.green,Color.yellow};
    
    
    public void init(){
    	int i,k;
        Font f=new Font("TimesRoman",Font.PLAIN,FONTSIZE1);
        setFont(f);
 
        setLayout(new BorderLayout());
        Panel p = new Panel();
        p.setLayout(new GridLayout(4,1));
        p.add(new Button("Start"));
        p.add(new Button("Stop")); 
        p.add(new Button("Strobo"));
        p.add(new Button("Reset"));
        add("East", p);


        initrk();//initialize for RK method
        drawinitflag=1;
        resize(500,400);
        setBackground(col);
        dim1=this.size();
        if (offScreen == null) {
	        offScreen = createImage(dim1.width,dim1.height);
	        offGraphics = offScreen.getGraphics();
        }
   }

	//calculation for the accelaration
	public void acce(){
		int i,j,k;
		double fw,fw1;
	
		if(swa||swc){
			for(i=0;i<=n;i++){
				if(swa){
					for(j=0;j<=i;j++){
						fw=0.;
						for(k=0;k<=dim;k++){
							if(i!=j){
								dx[i][j][k]=x1[i][k]-x1[j][k];
								dx[j][i][k]=x1[j][k]-x1[i][k];
							}
							else
								dx[i][j][k]=x1[i][k]-x0[j][k];
							fw+=dx[i][j][k]*dx[i][j][k];
						}
						r[i][j]=Math.sqrt(fw);
					
						for(k=0;k<=dim;k++){
							if(r[i][j]!=0)
								nrm[i][j][k]=dx[i][j][k]/r[i][j];
							else
								nrm[i][j][0]=1.;
							if(i!=j)
								nrm[j][i][k]=-nrm[i][j][k];
						}
						r[i][j]-=al[i][j];
						r[j][i]=r[i][j];
						if(ap[i][j]==0)
							pow[i][j]=1.;
						if(ap[i][j]==-2)
							pow[i][j]=1./r[i][j]/r[i][j];
						if(ap[i][j]==1)
							pow[i][j]=r[i][j];
						if(ap[i][j]==2){
							if(r[i][j]>al[i][j]){
								pow[i][j]=r[i][j]-al[i][j];
							}
							else{
								pow[i][j]=0.;
							}
						}
						pow[i][j]=pow[i][j]*aa[i][j];
						pow[j][i]=pow[i][j];
					}
				}
				fw1=0;
				for(k=0;k<=dim;k++)
					fw1+=v1[i][k]*v1[i][k];
				va[i]=Math.sqrt(fw1);
				for(k=0;k<=dim;k++){
					if(va[i]!=0.)
						vn[i][k]=v1[i][k]/va[i];
				}
			}
		}			

		for(i=0;i<=n;i++){
			for(k=0;k<=dim;k++)
				f[i][k]=0.;//clear
		}
		for(i=0;i<=n;i++){
			for(k=0;k<=dim;k++){
				if(swa){
					for(j=0;j<=n;j++)
						f[i][k]+=pow[i][j]*nrm[i][j][k];
				}
				if(swb)
					f[i][k]+=b[i]*v1[i][k];
				if(swc)
					f[i][k]+=c[i]*va[i]*va[i]*vn[i][k];
				if(swd)
					f[i][k]+=d[i][k];
				f[i][k]/=mass[i];
			}
		}		
	}
	
	//Runge-Kutta method
	public void rk(){
		int i,j,k,l;
		for(i=0;i<=n;i++){
			for(k=0;k<=dim;k++){
				x1[i][k]=x[i][k];
				v1[i][k]=v[i][k];
				w[i][k]=0.;
				w1[i][k]=0.;
			}
		}
		acce();
		for(l=0;l<=2;l++){
			for(i=0;i<=n;i++){
				for(k=0;k<=dim;k++){
					ik[l][i][k]=dt*v1[i][k];
					im[l][i][k]=dt*f[i][k];
					x1[i][k]=x[i][k]+ik[l][i][k]/coef[l+1];
					v1[i][k]=v[i][k]+im[l][i][k]/coef[l+1];
					w[i][k]+=ik[l][i][k]*coef[l];
					w1[i][k]+=im[l][i][k]*coef[l];
				}
			}
			acce();
		}
		for(i=0;i<=n;i++){
			for(k=0;k<=dim;k++){
				ik[l][i][k]=dt*v1[i][k];
				im[l][i][k]=dt*f[i][k];
				x1[i][k]=x[i][k]+(w[i][k]+ik[3][i][k])/6.;
				v1[i][k]=v[i][k]+(w1[i][k]+im[3][i][k])/6.;
			}
		}
		for(i=0;i<=n;i++){
			for(k=0;k<=dim;k++){
				x[i][k]=x1[i][k];
				v[i][k]=v1[i][k];
			}
		}
	}
	
	public void initrk(){
		int i,j;
		dim=1;//# of dimension-1
		n=2;//# ob bodies-1
		dt=.03;//time interval

		//initial position of a body x[i][n]�@i:body #,n:axis#
		//   x                y                 z
		x[0][0]=120 ; x[0][1]=0. ;
		x[1][0]=140 ; x[1][1]=0. ; 
		x[2][0]=0. ; x[2][1]=0.; 

		//position of fixed point
		//   x0              y0                 z0
		x0[0][0]=0. ; x0[0][1]=0. ; 
		x0[1][0]=0. ; x0[1][1]=0. ; 
		x0[2][0]=0. ; x0[2][1]=0. ; 

		//velosity v[i][n]�@i:body#,n:axis#
		//  v x             v y                 vz
		v[0][0]=0. ; v[0][1]=-18.; 
		v[1][0]=0. ; v[1][1]=-32. ;
		v[2][0]=0. ; v[2][1]=-(v[0][1]+v[1][1] *0.1)/10.;
	
		//mass
		mass[0]=1;
		mass[1]=0.1;
		mass[2]=10;
	
	//---setting of the forces-------	
		
		swa=true;//interaction between two bodies
		//strength
		aa[0][0]=0;
		aa[1][0]=-500.; aa[1][1]=0;
		aa[2][0]=-50000.; aa[2][1]=-5000.; aa[2][2]=0;
		//power
		ap[0][0]=0;
		ap[1][0]=-2; ap[1][1]=0;
		ap[2][0]=-2; ap[2][1]=-2; ap[2][2]=0;
		//length of spring
		al[0][0]=0.;
		al[1][0]=0.; al[1][1]=0.;
		al[2][0]=0.; al[2][1]=0.; al[2][2]=0.;
	
		if(n>0){//symmetrize
			for(i=1;i<=n;i++){
				for(j=0;j<i;j++){
					aa[j][i]=aa[i][j];
					ap[j][i]=ap[i][j];
					al[j][i]=al[i][j];
				}
			}
		}
	
		swb=false;//the force depend on the speed(traction)
		//b[0]=0.; b[1]=0.; b[2]=0.;
		
		swc=false;//the force depend on the squear of the speed
		//c[0]=0.; c[1]=0.; c[2]=-0.001.;	
		
		swd=false;//constant force
		//d[0][0]=0.; d[0][1]=9.8*mass[0];
		//d[1][0]=0.; d[1][1]=9.8*mass[1];
		//d[2][0]=0.; d[2][1]=9.8*mass[2];		
	}

     public void calc(){
 		rk();//call of Runge-Kutta 

   }

		public boolean mouseDrag(Event e,int xd,int yd){
			int i;
			if(!((yd>380)&&(xd>360)&&(xd<430))){
			i=targetn;
			repaint();
			v[i][0]=(double)(xd-x[i][0]-pt0.x)/2.;
			v[i][1]=(double)(yd-x[i][1]-pt0.y)/2.;
			}					
			return true;
		}
		
		public boolean mouseDown(Event e,int xd,int yd){
			int i;
			if((yd>380)&&(xd>365)&&(xd<425)){
				oldtargetn=targetn;
				targetn=(xd-365)/20;
				repaint();
			}		
			return true;
		}
				
   
        public boolean action(Event e, Object o) {
        if(e.target instanceof Button) {
             if ("Start".equals(o)) {
                drawinitflag=1;
                stepflag=0;
                drawmode = 2;
                calc();
                drawmode = 1;
             } 
             if ("Stop".equals(o)) {
                 stepflag=0;
                 drawmode = 2;
                 return true;
             }
             if ("Strobo".equals(o)) {
                 drawinitflag=1;
                 stepflag=1;
                 drawmode = 1;
                 return true;
             }
             if ("Reset".equals(o)) {
                 drawinitflag=1;
                 stepflag=0;
                 drawmode = 2;
                 initrk();
                 drawvflag=1;
                 repaint();
                 return true;
             }
             return true;
      }
      return super.handleEvent(e);
   }

    public void start(){
        if(th==null){
             th=new Thread(this);
             th.start();
        }
    }
    public void run(){
        while(th!=null){
             if(drawmode==1){
                 try{
                      calc();
                      calc();
                      calc();
                      calc();
                      calc();

                      repaint();
                      th.sleep(50);
                 }catch(InterruptedException e){
                       ;
                 }
              }
        }
    }
    public void stop(){
        if(th !=null){
            th.stop();
            th=null;
        }
    }
    public void update(Graphics g){
        paint(g);
    }
    public void paint(Graphics g){
    	int i,j,k;
        if(drawinitflag==1){
             offGraphics.setColor(getBackground());
             offGraphics.fillRect(0,0,dim1.width,dim1.height);
             drawinitflag=0;
        }
         if(stepflag !=1){
           		 offGraphics.setColor(getBackground());
	       		 offGraphics.fillRect(0,0,dim1.width,dim1.height);
		 }    
		
        for(i=0;i<=n;i++){

	        offGraphics.setColor(co[i]);
        	oldx[i][0]=pt0.x+(int)(x[i][0]-dd[i]*.5);
      		oldx[i][1]=pt0.y+(int)(x[i][1]-dd[i]*.5);
      		offGraphics.fillOval(oldx[i][0],oldx[i][1],dd[i],dd[i]);
      		offGraphics.fillOval(370+20*i,385,DD,DD);
      		
			offGraphics.setColor(Color.pink);
 			oldnv[i][0]=pt0.x+(int)(x[i][0]);
  			oldnv[i][1]=pt0.y+(int)(x[i][1]);
  			oldnv[i][2]=pt0.x+(int)(x[i][0]+v[i][0]*2.);
  			oldnv[i][3]=pt0.y+(int)(x[i][1]+v[i][1]*2.);
  			offGraphics.drawLine(oldnv[i][0],oldnv[i][1],oldnv[i][2],oldnv[i][3]);

      	}

			offGraphics.setColor(getBackground());
			offGraphics.fillOval(373+20*targetn,388,DD-6,DD-6);
      	offGraphics.setColor(Color.white);
      	offGraphics.drawString("Body selector",370,380);
      	g.drawImage(offScreen,0,0,this);
   }
}