// <applet code="GravityFr" width=500 height=500></applet>
// GravityFr.java (200810094) Fuat Bahadir
import java.applet.Applet;
import java.awt.*;
import java.awt.image.*;
public class GravityFr extends Applet
{
Image img;
int wd,ht,pix[],alpha;
public void init()
{
wd=getSize().width;ht=getSize().height;alpha=255;
pix=new int[wd*ht];
gr();
img=createImage(new MemoryImageSource(wd,ht,pix,0,wd));
}
public void paint(Graphics g)
{
g.drawImage(img,0,0,this);
// Refresh Periodically
long t=System.currentTimeMillis();
while((System.currentTimeMillis()-t)<10000) {;}
// delete the old graph
for(int i=0;i<wd*ht;++i) pix[i]=0;
gr();
img=createImage(new MemoryImageSource(wd,ht,pix,0,wd));
repaint();
}
/*
public void update(Graphics g) // to stop refresh flickering
{
paint(g);
}
*/
public void gr()
{
// fractal level
int level=100;
// number of gravity sources
int n = (int)(Math.random() * 6)+3;
double G = 1.0; // general gravity constant
double h = 0.0025; // time step (real solution; lim h->0)
double dmin = 10.0; // min allowed distance between objects
int mx, my, k, j, ix, iy;
mx = wd-1;my = ht-1;
double ang, v, dx, dy, d, a, ax, ay;
double x[], y[], xnew[], ynew[], m[], vx[], vy[];
double x0[], y0[], vx0[], vy0[];
m=new double[n];
x=new double[n];y=new double[n];
xnew=new double[n];ynew=new double[n];
vx=new double[n];vy=new double[n];
x0=new double[n];y0=new double[n];
vx0=new double[n];vy0=new double[n];
double Sx, Sy, Svx, Svy, Sm;
Sx = Sy = Svx = Svy = Sm = 0;
for(k=0;k<n;++k)
{
x[k] = (double)((Math.random()*2-1) * mx/2+mx/2);
y[k] = (double)((Math.random()*2-1) * my/2+my/2);
m[k] = (double)(Math.random() * 30) + 10;
m[k] = (m[k]*m[k]*m[k])*40;
ang = (double)(Math.random() * 2 * Math.PI);
v = (double)(Math.random() * 200);
vx[k] = (double)(v * Math.cos(ang));
vy[k] = (double)(v * Math.sin(ang));
Sx = Sx + m[k] * x[k];
Sy = Sy + m[k] * y[k];
Svx = Svx + m[k] * vx[k];
Svy = Svy + m[k] * vy[k];
Sm = Sm + m[k];
}
for (k = 0; k < n; k++)
{
x[k] = x[k] - (Sx / Sm) + (mx / 2.0);
y[k] = y[k] - (Sy / Sm) + (my / 2.0);
vx[k] = vx[k] - (Svx / Sm);
vy[k] = vy[k] - (Svy / Sm);
}
for (k = 0; k < n; k++)
{
x0[k] = x[k];
y0[k] = y[k];
vx0[k] = vx[k];
vy0[k] = vy[k];
}
// color palette
int rd[], gr[], bl[];
rd=new int[16];gr=new int[16];bl=new int[16];
for(k=0;k<16;k++)
{
rd[k] = (int)(Math.random() * 256);
gr[k] = (int)(Math.random() * 256);
bl[k] = (int)(Math.random() * 256);
}
//
for(iy=0;iy<my;iy++)
{
for(ix=0;ix<mx;ix++)
{
// load the initial values
for (k = 0; k < n; k++)
{
x[k] = x0[k];
y[k] = y0[k];
vx[k] = vx0[k];
vy[k] = vy0[k];
}
x[0]=ix;y[0]=iy;
for(int fr=0;fr<level;fr++)
{
// n-body simulation
for(k=0;k<n;++k)
{
ax = 0; ay = 0;
for(j=0;j<n;++j)
{
if(k!=j)
{
dx = x[j] - x[k]; dy = y[j] - y[k];
d = (double)Math.sqrt(dx * dx + dy * dy);
d = Math.max(dmin, d);
dx = dx / d; dy = dy / d;
a = G * m[j] / (d * d);
ax = ax + a * dx; ay = ay + a * dy;
}
}
xnew[k] = x[k] + vx[k] * h;
ynew[k] = y[k] + vy[k] * h;
vx[k] = vx[k] + ax * h; vy[k] = vy[k] + ay * h;
}
for(k=0;k<n;++k)
{
x[k] = xnew[k]; y[k] = ynew[k];
}
}
dx = x[0] - ix; dy = y[0] - iy;
d = (double)Math.sqrt(dx * dx + dy * dy);
pix[wd*iy+ix]=(alpha<<24)|(rd[((int)d*100)%16]<<16)|(gr[((int)d*100)%16]<<8)|bl[((int)d*100)%16];
}
}
}
}
