打开gl窗口不显示？

Question

#include <iostream>
#include <stdio.h>
#include <GL/glut.h>
#include <windows.h>
#include <math.h>

using namespace std;
void display(void) {
    float cx = 200, cy = 200, rad = 50;
    float startx = cx - rad;
    float starty = cy;
    int x = startx, y = starty;

    glColor3f(1.0f, 0.0f, 0.0f);
    glBegin(GL_POINTS);
    glVertex2f((x - 250.f) / 250.f, (250.f - y) / 250.f);

    while (x < cx + rad) {    
        x++;
        y = cy - sqrt(rad * rad - (x - cx) * (x - cx));
        // y = sqrt(rad*rad - (x-cx)*(x-cx))-cy;
        glVertex2f((x - 250.f) / 250.f, (250.f - y) / 250.f);
        cout << x << " " << y << endl;
    }

    glFlush();    
    glEnd();
}

int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize(500, 500);
    gebtutInitWindowPosition(100, 100);
    glutCreateWindow("CpViewer");
    glClearColor(1.0, 1.0, 1.0, 0.0);
    glClear(GL_COLOR_BUFFER_BIT);
    glutDisplayFunc(display);
    glutMainLoop();

    return 0;
}

I am trying to implement an algo to drawn a circle but im not getting any output. i am also not able to see the opengl graphics window it appears transparent . what's wrong with this code.??

Answer 1

You are requesting a double-buffered window with that GLUT_DOUBLE flag. But you never swap the buffers. So what happens is that you draw all the time into the back buffer, and the front buffer is just undefined and nothing will ever be shown.

You should add a glutSwapBuffer() call when you finished drawing a frame, typically at the very end of your display() function. And while you're at it: Remove that glFlush() call. You put it inside an glBegin()/glEnd() block, where it will not work at all, and you won't need it. Also make sure that the glutSwapBuffers() call is added after the glEnd() .