Practical-4 || CG || midpoint Ellipse Drawing Algorithm.cpp

//CG
#include<iostream.h>
#include<conio.h>
#include<math.h>
#include<stdlib.h>
#include<dos.h>
#include<graphics.h>
#include<ctype.h>
//function prototyping
void ellipseplotter(float rx,float ry,float cx,float cy);
//ellipse plotting function
void ellipseplotter(float rx,float ry,float cx, float cy){
  // Region 1 start here
  float x=0.0;
  float y=ry;
  float p1=(ry*ry)-(rx*rx*ry)+((rx*rx)*0.25);// initialized the p1
  putpixel(cx,cy,WHITE);
  while((2*ry*ry*x)<(2*rx*rx*y)){
    x++;
    if(p1<0){
      p1=p1+(2*ry*ry*x)+(ry*ry);
    }
    else{
      y--;
      p1=p1+(2*ry*ry*x)-(2*rx*rx*y)+(ry*ry);
    }
    putpixel(x+cx,y+cy,WHITE);
    putpixel(-x+cx,y+cy,RED);
    putpixel(-x+cx,-y+cy,BLUE);
    putpixel(x+cx,-y+cy,GREEN);
  }
  // Region 2 start here
  float p2=(ry*ry)*((x+(0.5))*(x+(0.5)))+(rx*rx*(y-1)*(y-1))-(rx*rx*ry*ry);// initialized the p2
  while(y>0){
    if(p2>0){
      //x=x;
      y--;
      p2=p2-(2*rx*rx*y)+(rx*rx);
    }
    else{
      x++;
      y--;
      p2=p2+(2*ry*ry*x)-(2*rx*rx*y)+(rx*rx);
    }
    putpixel(x+cx,y+cy,WHITE);
    putpixel(-x+cx,y+cy,RED);
    putpixel(-x+cx,-y+cy,BLUE);
    putpixel(x+cx,-y+cy,GREEN);
  }
}
//todo main function
void main(){
  clrscr();
  int gd=DETECT,gm;
  float rx,ry,cx,cy;
  initgraph(&gd,&gm,"C:\\TURBOC3\\BGI");
  cleardevice();
  cout<<"\n--------------Ellipse Drawing Algorithm--------------";
  cout<<"\nEnter the coordinates of the centre of the Ellipse\n";
  cin>>cx>>cy;
  cout<<"\nEnter the Length of the Rx of the circle\n";
  cin>>rx;
  cout<<"\nEnter the Length of the Ry of the circle\n";
  cin>>ry;
  ellipseplotter(rx,ry,cx,cy);
  getch();
  closegraph();
}