椭圆算法图形学

#include"stdio.h"
#include"graphics.h"
#include"conio.h"
void Ty(int x0,int y0,double a,double b,int color)
{
   double x,y,d;
   int t;
   x=0;
   y=b;
   d=b*b+a*a*(0.25-b);
   while(y>=0)
   {
        putpixel(x0+x,y0+y,color);
        putpixel(x0+x,y0-y,color);
        putpixel(x0-x,y0+y,color);
        putpixel(x0-x,y0-y,color);
    if(2*b*b*x<=2*a*a*y)
      {  if(d<=0)
         {d+=b*b*(2*x+3);x++;}
        else
        {d+=b*b*(2*x+3)+a*a*(-2*y+2);x++;y--;}
      }
        else
        {
        if(d<=0)
        {d+=b*b*(2*x+2)+a*a*(-2*y+3);x++;y--;}
        else
        {d+=a*a*(-2*y+3);y--;}
        }