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P. 71
Unit 5: Implementing Ellipse Algorithm
p=(ry 1 –rx 1 *ry+(0.25*rx 1 )); Notes
px=0;
py=rx 2 *y;
while(px<py)
{
x=x+1;
px=px+ry 2 ;
if(p>=0)
y=y–1;
py=py–rx 2 ;
if(p<0)
p=p+ry1+px;
else
p=p+ry 1 +px–py;
plotpoints(xcenter,ycenter,x,y);
/* REGION 2*/
p=(ry 1 *(x+0.5)*(x+0.5)+rx1*(y–1)*(y–1)–rx 1 *ry 1 );
while(y>0)
{
y=y–1;
py=py–rx 2 ;
if(p<=0)
{
x=x+1;
px=px+ry 2 ;
}
if(p>0)
p=p+rx 1 –py;
else
p=p+rx 1 –py+px;
plotpoints(xcenter,ycenter,x,y);
}
}
getch();
return(0);
}
int plotpoints(int xcenter,int ycenter,int x,int y)
{
putpixel(xcenter+x,ycenter+y,6);
putpixel(xcenter–x,ycenter+y,6);
putpixel(xcenter+x,ycenter–y,6);
putpixel(xcenter–x,ycenter–y,6);
}
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