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Editorial Team
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Asked: 2026-06-01T03:38:32+00:00

I’m using OpenGL with C++ in dev-c++ IDE. When I draw a circle, nothing

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I’m using OpenGL with C++ in dev-c++ IDE.
When I draw a circle, nothing happens, what can be wrong?

int WINAPI WinMain (HINSTANCE hInstance,
                    HINSTANCE hPrevInstance,
                    LPSTR lpCmdLine,
                    int iCmdShow)
{
    WNDCLASS wc;
    HWND hWnd;
    HDC hDC;
    HGLRC hRC;        
    MSG msg;
    BOOL bQuit = FALSE;
    float theta = 0.0f;

    /* register window class */
    wc.style = CS_OWNDC;
    wc.lpfnWndProc = WndProc;
    wc.cbClsExtra = 0;
    wc.cbWndExtra = 0;
    wc.hInstance = hInstance;
    wc.hIcon = LoadIcon (NULL, IDI_APPLICATION);
    wc.hCursor = LoadCursor (NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH) GetStockObject (BLACK_BRUSH);
    wc.lpszMenuName = NULL;
    wc.lpszClassName = "GLSample";
    RegisterClass (&wc);

    /* create main window */
    hWnd = CreateWindow (
      "GLSample", "OpenGL Sample", 
      WS_CAPTION | WS_POPUPWINDOW | WS_VISIBLE,
      0, 0, 768, 512,
      NULL, NULL, hInstance, NULL);

    /* enable OpenGL for the window */
    EnableOpenGL (hWnd, &hDC, &hRC);

    /* program main loop */
    while (!bQuit)
    {
        /* check for messages */
        if (PeekMessage (&msg, NULL, 0, 0, PM_REMOVE))
        {
            /* handle or dispatch messages */
            if (msg.message == WM_QUIT)
            {
                bQuit = FALSE;
            }
           else
           {
                TranslateMessage (&msg);
                DispatchMessage (&msg);
            }
        }
       else
        {
            /* OpenGL animation code goes here */

            glClearColor (0.0f, 0.0f, 0.0f, 0.0f);
            glClear (GL_COLOR_BUFFER_BIT);

            glPushMatrix ();

            circle(30,30,20,3);


            glPopMatrix ();

            SwapBuffers (hDC);

        }
    }

    /* shutdown OpenGL */
    DisableOpenGL (hWnd, hDC, hRC);

    /* destroy the window explicitly */
    DestroyWindow (hWnd);

    return msg.wParam;
}
void circle(float x, float y, float r, int segments)
{
    glBegin( GL_TRIANGLE_FAN );
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);
        glVertex2f(x, y);
        for( int n = 0; n <= segments; ++n ) {
            float const t = 2*M_PI*(float)n/(float)segments;
            glVertex2f(x + sin(t)*r, y + cos(t)*r);
        }
    glEnd();
}
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1 Answer

  1. Editorial Team

    First of all you cannot put restricted calls inside of a glBegin() block. (glMatrixMode, glLoadIdentity, glOrtho, etc). You should start checking for opengl errors with glGetError in several places in your code. If you have any errors reported (and you surely do) that should be the first step in any debugging process.

    Also get familiar with the man pages for each command, they can help you understand how to use them:

    http://www.opengl.org/sdk/docs/man/xhtml/glBegin.xml

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