while(y>x) {float fx=normalize(x);float fy=normalize(y);//(x,y) (-x,-y) (-x,y) (x,-y)glVertex2f(fcx+fx,fcy+fy);glVertex2f(fcx-fx,fcy-fy);glVertex2f(fcx-fx,fcy+fy);glVertex2f(fcx+fx,fcy-fy);//(y,x) (-y,-x) (-y,x) (y,-x)glVertex2f(fcx+fy,fcy+fx);glVertex2f(fcx-fy,fcy-fx);glVertex2f(fcx-fy,fcy+fx);glVertex2f(fcx+fy,fcy-fx);if(d<0) {d=d+2*x+3;} else {d=d+2*(x-y)+5;--y;}++x;}

            //need the 4 points on the diagonalfloat diagonal=float(r)/sqrt(2);glVertex2f(fcx+diagonal,fcy+diagonal);glVertex2f(fcx-diagonal,fcy+diagonal);glVertex2f(fcx+diagonal,fcy-diagonal);glVertex2f(fcx-diagonal,fcy+diagonal);

 1 #include <iostream>
 2 #include <math.h>
 3 #include <GLFW/glfw3.h>
 4 using namespace std;
 5 //g++ -o demo circle.cpp -lglfw3 -framework Cocoa -framework OpenGL -framework IOKit -framework CoreVideo
 6 float normalize(int input) {
 7     return float(input)/500;
 8 }
 9
10 //-400 100 200
11 int main() {
12     int r, cx,cy;
13     cout << "Please give the coordinate of the center of the circle? like 'x y'" << endl
14     << "Notice: x and y should be integers between 0 and 500" << endl;
15     cin >> cx >> cy;
16     cout << "Please give the radius r of the circle" << endl
17     << "Notice: r should be an integer between 0 and 500" << endl;
18     cin >> r;
19     float fcx=normalize(cx);
20     float fcy=normalize(cy);
21
22     int x=0,y=r;
23     int d=1-r;
24
25
26     bool init = true;
27     if(!glfwInit()) {
28         cout << "Initialization failed" << endl;
29         init = false;
30         return -1;
31     }
32
33     //create a window with its OpenGL context
34     GLFWwindow* window1 = glfwCreateWindow(640, 640, "Circle", NULL, NULL);
35
36     if (!window1) {
37         cout << "Window or OpenGL context creation failed" << endl;
38         glfwTerminate();
39         return -1;
40     }
41     if(init&&window1) {
42         // Make the window's context current */
43         glfwMakeContextCurrent(window1);
44
45         while (!glfwWindowShouldClose(window1)) {
46             // Keep running
47             /* Draw a triangle */
48             glBegin(GL_POINTS);
49
50             glColor3f(1, 0.52, 0.0);    // Orange
51             //glVertex2f
52
53             while(y>x) {
54                 float fx=normalize(x);
55                 float fy=normalize(y);
56                 //(x,y) (-x,-y) (-x,y) (x,-y)
57                 glVertex2f(fcx+fx,fcy+fy);
58                 glVertex2f(fcx-fx,fcy-fy);
59                 glVertex2f(fcx-fx,fcy+fy);
60                 glVertex2f(fcx+fx,fcy-fy);
61
62                 //(y,x) (-y,-x) (-y,x) (y,-x)
63                 glVertex2f(fcx+fy,fcy+fx);
64                 glVertex2f(fcx-fy,fcy-fx);
65                 glVertex2f(fcx-fy,fcy+fx);
66                 glVertex2f(fcx+fy,fcy-fx);
67
68                 if(d<0) {
69                     d=d+2*x+3;
70                 } else {
71                     d=d+2*(x-y)+5;
72                     --y;
73                 }
74                 ++x;
75             }
76             //need the 4 points on the diagonal
77             float diagonal=float(r)/sqrt(2);
78             glVertex2f(fcx+diagonal,fcy+diagonal);
79             glVertex2f(fcx-diagonal,fcy+diagonal);
80             glVertex2f(fcx+diagonal,fcy-diagonal);
81             glVertex2f(fcx-diagonal,fcy+diagonal);
82
83             x=0;
84             y=r;
85
86
87             glEnd();

 62                 //(y,x) (-y,-x) (-y,x) (y,-x)63                 glVertex2f(fcx+fy,fcy+fx);64                 glVertex2f(fcx-fy,fcy-fx);65                 glVertex2f(fcx-fy,fcy+fx);66                 glVertex2f(fcx+fy,fcy-fx);