C/C++ - Come si rende solida un immagine con le Open-gl

uso Dev-C++ e sono alle prime armi con le open-gl. ho provato a disegnare un tetraedro in /* animation code goes here */, ma il problema sorge durante la rotazione, perchè l'immagine perde la sua compattezza. qualcuno mi saprebbe aiutare, grazie in anticipo? [insieme al codice allego anche il progetto]

/************************** 
* Includes 
* 
**************************/ 

#include <windows.h> 
#include <gl/gl.h> 


/************************** 
* Function Declarations 
* 
**************************/ 

LRESULT CALLBACK WndProc (HWND hWnd, UINT message, 
WPARAM wParam, LPARAM lParam); 
void EnableOpenGL (HWND hWnd, HDC *hDC, HGLRC *hRC); 
void DisableOpenGL (HWND hWnd, HDC hDC, HGLRC hRC); 


/************************** 
* WinMain 
* 
**************************/ 

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, 500, 500, 
      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 = TRUE; 
            } 
            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 (); 
            glRotatef (theta, 0.0f, theta, 0.0f); 
            glBegin (GL_TRIANGLES); 
             
            glColor3f (1.0f, 0.0f, 0.0f);   glVertex3f ( 0.0f,  0.0f,  1.0f); 
            glColor3f (0.0f, 1.0f, 0.0f);   glVertex3f ( 0.8f,  0.0f, -0.5f); 
            glColor3f (0.0f, 0.0f, 1.0f);   glVertex3f (-0.8f,  0.0f, -0.5f); 
             
            glColor3f (1.0f, 0.0f, 1.0f);   glVertex3f ( 0.0f,  0.0f,  1.0f); 
            glColor3f (0.0f, 1.0f, 0.0f);   glVertex3f ( 0.8f,  0.0f, -0.5f); 
            glColor3f (1.0f, 0.0f, 1.0f);   glVertex3f ( 0.0f,  0.8f,  0.0f); 
             
            glColor3f (0.0f, 1.0f, 0.0f);   glVertex3f ( 0.8f,  0.0f, -0.5f); 
            glColor3f (0.0f, 1.0f, 1.0f);   glVertex3f (-0.8f,  0.0f, -0.5f); 
            glColor3f (1.0f, 1.0f, 0.0f);   glVertex3f ( 0.0f,  0.8f,  0.0f); 
             
            glColor3f (1.0f, 0.0f, 0.0f);   glVertex3f ( 0.0f,  0.8f,  0.0f); 
            glColor3f (0.0f, 1.0f, 1.0f);   glVertex3f (-0.8f,  0.0f, -0.5f); 
            glColor3f (1.0f, 0.0f, 1.0f);   glVertex3f ( 0.0f,  0.0f,  1.0f); 
                         
            glColor3f (0.0f, 1.0f, 0.0f);   glVertex3f ( 0.8f,  0.0f, -0.5f); 
            glColor3f (0.0f, 1.0f, 1.0f);   glVertex3f (-0.8f,  0.0f, -0.5f); 
            glColor3f (1.0f, 1.0f, 0.0f);   glVertex3f ( 0.0f, -0.8f,  0.0f); 
             
            glColor3f (1.0f, 0.0f, 0.0f);   glVertex3f ( 0.0f, -0.8f,  0.0f); 
            glColor3f (0.0f, 1.0f, 1.0f);   glVertex3f (-0.8f,  0.0f, -0.5f); 
            glColor3f (1.0f, 0.0f, 1.0f);   glVertex3f ( 0.0f,  0.0f,  1.0f); 
            glEnd (); 
            glPopMatrix (); 

            SwapBuffers (hDC); 

            theta = theta+1.0f; 
            Sleep (1); 
        } 
    } 

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

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

    return msg.wParam; 
} 


/******************** 
* Window Procedure 
* 
********************/ 

LRESULT CALLBACK WndProc (HWND hWnd, UINT message, 
                          WPARAM wParam, LPARAM lParam) 
{ 

    switch (message) 
    { 
    case WM_CREATE: 
        return 0; 
    case WM_CLOSE: 
        PostQuitMessage (0); 
        return 0; 

    case WM_DESTROY: 
        return 0; 

    case WM_KEYDOWN: 
        switch (wParam) 
        { 
        case VK_ESCAPE: 
            PostQuitMessage(0); 
            return 0; 
        } 
        return 0; 

    default: 
        return DefWindowProc (hWnd, message, wParam, lParam); 
    } 
} 


/******************* 
* Enable OpenGL 
* 
*******************/ 

void EnableOpenGL (HWND hWnd, HDC *hDC, HGLRC *hRC) 
{ 
    PIXELFORMATDESCRIPTOR pfd; 
    int iFormat; 

    /* get the device context (DC) */ 
    *hDC = GetDC (hWnd); 

    /* set the pixel format for the DC */ 
    ZeroMemory (&pfd, sizeof (pfd)); 
    pfd.nSize = sizeof (pfd); 
    pfd.nVersion = 1; 
    pfd.dwFlags = PFD_DRAW_TO_WINDOW | 
      PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER; 
    pfd.iPixelType = PFD_TYPE_RGBA; 
    pfd.cColorBits = 24; 
    pfd.cDepthBits = 16; 
    pfd.iLayerType = PFD_MAIN_PLANE; 
    iFormat = ChoosePixelFormat (*hDC, &pfd); 
    SetPixelFormat (*hDC, iFormat, &pfd); 

    /* create and enable the render context (RC) */ 
    *hRC = wglCreateContext( *hDC ); 
    wglMakeCurrent( *hDC, *hRC ); 

} 


/****************** 
* Disable OpenGL 
* 
******************/ 

void DisableOpenGL (HWND hWnd, HDC hDC, HGLRC hRC) 
{ 
    wglMakeCurrent (NULL, NULL); 
    wglDeleteContext (hRC); 
    ReleaseDC (hWnd, hDC); 
}