Circle_MidPoint.cpp

#include<stdio.h>
#include<graphics.h>
#include<conio.h>
// pre-processor directories to calculate co-ordinates for the displaying device
#define fx(x) (getmaxx()/2+x)    
#define fy(y) (getmaxy()/2-y)

// required constants
#define X 640
#define Y 480
// colors
#define LWHITE 7
#define LCYAN 3

void drawQuadrants();   // function prototype to create quadrants
void circleMidPointApp(int,int,int); // function prototype to draw a circle through Mid-Point Approach
void paint(int,int,int,int);   // function prototype to plot 8 different points of a circle at once at a time


int main(void)
/* 
   Variable Description:-
            (x1,y1) is the co-ordinate of the center of the circle. 
            'r' is the radius. 
            'x' is the abcissa of the starting point from where plotting is to begin.
            'y' is the ordinate of the starting point from where plotting is to begin.
            'd' is the decision parameter
            'speed' is basically the time(in milliseconds) for which a delay will be applied
   
            Note: Variables 'x1','y1','r' and 'speed' are initialized from before in this piece of code. To avoid any loss of generality, take user-inputs.
   
   Functions used:-
          Pre-defined functions:   
             initwindow() - to create the displaying screen.
             setcolor()- to color everything drawn after that that segment till the same function has been invoked with a different color.
             delay() - to hold the current state for a particular time
             putpixel()- to color the pixel (x,y) with a given color, say C (passed as an integer).
          User-defined functions:
             drawQuadrants() -  to draw four quadrants of the window.
             circleMidPointApp() - o draw a circle through Mid-Point Approach.
             paint() - plot 8 different points of a circle at once at a time
             
   Logic Description:- 
           For the first quadrant start form (0,r), increments 'x' by '1' and find corresponding 'y' and plot the (x,y) pixel. 
           Repeat the process till 'x' and 'y' are unequal. For each quadrant find the reflecting points of the 8 octants and plot them too.
           
          Algorithm:
              di+1=di+2(xi+1)+1, if di<0, E(xi+1,yi)  (Eastern pixel)
              di+1=di+2(xi+1)+1-2(yi-1),  if di>=0, SE(xi+1,yi-1)  (South-Eastern pixel)
          
          Initially: 
              d0=5/4-r = 1-r (appx).                 
*/
{
    // declaring and initializing variables
    int x1=0,y1=0,r=150;
    initwindow(X,Y);     // creating window
    drawQuadrants(); // calling function to draw quadrants 
    circleMidPointApp(x1,y1,r);   // function call to draw a circle through Mid-Point Approach
    getch();
    return 0;
}  // end of main

// function definition to create quadrants
void drawQuadrants()
{
    setcolor(LCYAN);   // setting a color for the co-ordinate axes
    line(0,fy(0),X,fy(0));   // drawing the X-axis; fy(0)=480/2=240;
    line(fx(0),0,fx(0),Y);   // drawing the Y-axis; fx(0)=640/2=320;
}

// function definition to draw a circle through Mid-Point Approach
void circleMidPointApp(int x1,int y1,int r)
{
     // declaring and initializing variables
     int x=0,y,speed=50,d;
     y=r;
     d=1-r;
     // applying Mid-point algorithm
     while(x<=y)
     {          
              paint(x1,y1,x,y);    // function call to plot 8 different points of a circle at once at a time
              if(d<0)  // if decision variable is negative, E corner
                  d=d+(2*x)+3;
              else   // if decision variable is non-negative, SE corner
              {
                  d=d+(2*(x-y))+5;
                  y=y-1;
              }
              x=x+1; 
              delay(speed);    // holding the present state for 'speed' milliseconds
     }
}

// function definition to plot 8 different points of a circle at once at a time
void paint(int x1,int y1,int x,int y)
{
     // first quadrant
     putpixel(fx(x1+x),fy(y1-y),LWHITE);  // starting from (0,r) and drawing the half semi-circle, left to right
     putpixel(fx(x1+y),fy(y1-x),LWHITE);   // starting from (r,0) and drawing the half semi-circle, right to left
     // second quadrant
     putpixel(fx(x1-x),fy(y1-y),LWHITE);  // starting from (0,r) and drawing the half semi-circle, right to left
     putpixel(fx(x1-y),fy(y1-x),LWHITE);   // starting from (-r,0) and drawing the half semi-circle, left to right
     // third quadrant
     putpixel(fx(x1-x),fy(y1+y),LWHITE); // starting from (0,-r) and drawing the half semi-circle, right to left
     putpixel(fx(x1-y),fy(y1+x),LWHITE);   // starting from (-r,0) and drawing the half semi-circle, left to right
     // fourth quadrant
     putpixel(fx(x1+y),fy(y1+x),LWHITE);  // starting from (r,0) and drawing the half semi-circle, right to left
     putpixel(fx(x1+x),fy(y1+y),LWHITE); // starting from (0,-r) and drawing the half semi-circle, left to right
}