Opengl,C++ : Draw Circle With Bresenham’s Circle Algorithm

1:  #include<stdio.h>  
2:  #include<GL/glut.h>  
3:  #include<math.h>  
4:  int ww=400,wh=400;  
5:  int first=0;  
6:  int xi,yi,xf,yf;  
7:  void putpixel(int x,int y)  
8:  {  
9:       glBegin(GL_POINTS);  
10:            glVertex2i(x,y);  
11:       glEnd();  
12:       glFlush();  
13:  }  
14:  int round(double n)  
15:  {  
16:       return (n>=0)?(int)(n+0.5):(int)(n-0.5);  
17:  }  
18:  void Bresenham_circle(int r)  
19:  {  
20:       int x=0,y=r,d=3-2*r;  
21:       while(x<=y){  
22:            //Here Transform each x,y coordinates by 250 pixels   
23:            putpixel(250+x, 250+y);  
24:            putpixel(250+y, 250+x);  
25:            putpixel(250-x, 250+y);  
26:            putpixel(250-x, 250-y);  
27:            putpixel(250-y, 250+x);  
28:            putpixel(250-y, 250-x);  
29:            putpixel(250+y, 250-x);  
30:            putpixel(250+x, 250-y);  
31:            if(d<0)  
32:                 d=d+(4*x)+6;  
33:            else{  
34:                 d=d+(4*(x-y))+10;  
35:                 y--;  
36:            }  
37:            x++;  
38:       }  
39:  }  
40:  void display()  
41:  {  
42:       glClearColor(0.4,0.7,0.2,1.0);  
43:       glColor3f(0.5,0.3,0.0);  
44:       glClear(GL_COLOR_BUFFER_BIT);  
45:       glutSwapBuffers();  
46:       glFlush();  
47:  }  
48:  void mouse(int btn,int state,int y,int x)  
49:  {  
50:       if(btn==GLUT_LEFT_BUTTON && state==GLUT_DOWN)  
51:       {  
52:            xi=0;  
53:            yi=y;  
54:            Bresenham_circle(yi);  
55:       }  
56:  }  
57:  void myinit()  
58:  {  
59:       glViewport(0,0,ww,wh);  
60:       glMatrixMode(GL_PROJECTION);  
61:       glLoadIdentity();  
62:       gluOrtho2D(0.0,(GLdouble)ww,0.0,(GLdouble)wh);  
63:       glMatrixMode(GL_MODELVIEW);  
64:  }  
65:  int main(int argc,char** argv)  
66:  {  
67:       glutInit(&argc,argv);  
68:       glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);  
69:       glutInitWindowSize(ww,wh);  
70:       glutCreateWindow("Bresenham-Circle");  
71:       glutDisplayFunc(display);  
72:       myinit();  
73:       glutMouseFunc(mouse);  
74:       glutMainLoop();  
75:       return 0;  
76:  }