#include<conio.h>
#include<stdio.h>
#include<graphics.h>
void main()
{
int gd=DETECT,gm;
float x,y,xc,yc,rx,ry,pk,pk1;
clrscr();
initgraph(&gd,&gm,"..\\bgi");
printf("Mid point ellipse drawing algorithm\n");
printf("Enter Center for ellipse\nx : ");
scanf("%f",&xc);
printf("y : ");
scanf("%f",&yc);
printf("Enter x-radius and y-radius\nx-radius : ");
scanf("%f",&rx);
printf("y-radius : ");
scanf("%f",&ry);
x=0;
y=ry;
pk=(ry*ry)-(rx*rx*ry)+((rx*rx)/4);
while((2*x*ry*ry)<(2*y*rx*rx))
{
if(pk<=0)
{
x=x+1;
pk1=pk+(2*ry*ry*x)+(ry*ry);
}
else
{
x=x+1;
y=y-1;
pk1=pk+(2*ry*ry*x)-(2*rx*rx*y)+(ry*ry);
}
pk=pk1;
putpixel(xc+x,yc+y,2);
putpixel(xc-x,yc+y,2);
putpixel(xc+x,yc-y,2);
putpixel(xc-x,yc-y,2);
}
pk=((x+0.5)*(x+0.5)*ry*ry)+((y-1)*(y-1)*rx*rx)-(rx*rx*ry*ry);
while(y>0)
{
if(pk>0)
{
y=y-1;
pk1=pk-(2*rx*rx*y)+(rx*rx);
}
else
{
x=x+1;
y=y-1;
pk1=pk+(2*ry*ry*x)-(2*rx*rx*y)+(rx*rx);
}
pk=pk1;
putpixel(xc+x,yc+y,2);
putpixel(xc-x,yc+y,2);
putpixel(xc+x,yc-y,2);
putpixel(xc-x,yc-y,2);
}
line(xc+rx,yc,xc-rx,yc);
line(xc,yc+ry,xc,yc-ry);
outtextxy(xc+(1.2*rx),yc-(1.2*ry),"(x,y)");
outtextxy(xc-(1.2*rx),yc+(1.2*ry),"(-x,-y)");
outtextxy(xc+(1.2*rx),yc+(1.2*ry),"(x,-y)");
outtextxy(xc-(1.2*rx),yc-(1.2*ry),"(-x,y)");
getch();
}