Opengl을 보고 있는데.. 그림이 그려지질 않습니다.
일단, 선만이라도 그려보고 싶은데...
초기화는 제대로 된건지, 어떤 부분이 잘못됐는지 잘 모르겠습니다.

QnA 에서 어떤분이 Opengl 초기화 하는법에 대해서 질문 올린것을 그대로 해보았습니다.
질문올린 분께서는 하얀화면과 검은화면이 깜박인다고 하시는데.. 저는 검은 화면만 보입니다.

질문에 답을 다신 분은 glFlush();를 초기화하는 부분에만 적용해보라고 하셨는데..
그렇게도 해보았는데도, 여전히 검은 화면만 보입니다.

내공이 부족한지라, 인터넷 검색을 해보아도 잘 이해가 안되네요..
가르침 부탁드립니다...


//---------------------------------------------------------------------------
//---------------------------------------------------------------------------
//---------------------------------------------------------------------------
class TForm3 : public TForm
{
__published:    // IDE-managed Components
    void __fastcall FormClose(TObject *Sender, TCloseAction &Action);
    void __fastcall FormCloseQuery(TObject *Sender, bool &CanClose);
    void __fastcall FormCreate(TObject *Sender);
    void __fastcall FormDestroy(TObject *Sender);
    void __fastcall FormShow(TObject *Sender);
    void __fastcall FormResize(TObject *Sender);
    void __fastcall FormPaint(TObject *Sender);
private:    // User declarations
    HDC hdc;
        HGLRC hrc;
    int PixelFormat;

public:        // User declarations
    __fastcall TForm3(TComponent* Owner);

        void __fastcall RenderGLScene();
        void __fastcall SetupRC();
    void __fastcall SetPixelFormatDescriptor();
        void __fastcall RenderScene();

};
//---------------------------------------------------------------------------
extern PACKAGE TForm3 *Form3;
//---------------------------------------------------------------------------
//---------------------------------------------------------------------------
//---------------------------------------------------------------------------


//---------------------------------------------------------------------------
//---------------------------------------------------------------------------
//---------------------------------------------------------------------------
__fastcall TForm3::TForm3(TComponent* Owner)
    : TForm(Owner)
{
//
}
//---------------------------------------------------------------------------
void __fastcall TForm3::FormClose(TObject *Sender, TCloseAction &Action)
{
//   
}
//---------------------------------------------------------------------------
void __fastcall TForm3::FormCloseQuery(TObject *Sender, bool &CanClose)
{
//
}
//---------------------------------------------------------------------------
void __fastcall TForm3::FormCreate(TObject *Sender)
{
//
    hdc = GetDC(Handle);
        SetPixelFormatDescriptor();
    hrc = wglCreateContext(hdc);
        wglMakeCurrent(hdc, hrc);
    SetupRC();

}
//---------------------------------------------------------------------------
void __fastcall TForm3::FormDestroy(TObject *Sender)
{
//
    //    ReleaseDC(Handle, hdc);
        wglMakeCurrent(hdc, NULL);
    wglDeleteContext(hrc);
}
//---------------------------------------------------------------------------
void __fastcall TForm3::FormShow(TObject *Sender)
{
//

}
//---------------------------------------------------------------------------
void __fastcall TForm3::FormResize(TObject *Sender)
{
//
    GLfloat nRange = 200.0f;
    glViewport(0, 0, ClientWidth, ClientHeight);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    if (ClientWidth <= ClientHeight)
       glOrtho(-nRange, nRange, -nRange*ClientHeight/ClientWidth,
                nRange*ClientHeight/ClientWidth, -nRange, nRange);
    else
       glOrtho(-nRange*ClientWidth/ClientHeight, nRange*ClientWidth/ClientHeight,
                -nRange, nRange, -nRange, nRange);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

}
//---------------------------------------------------------------------------
void __fastcall TForm3::RenderGLScene()
{
    //Place your OpenGL drawing code here

    RenderScene();

}
//---------------------------------------------------------------------------
void __fastcall TForm3::SetPixelFormatDescriptor()
{
    PIXELFORMATDESCRIPTOR pfd = {
        sizeof(PIXELFORMATDESCRIPTOR),
        1,
        PFD_DRAW_TO_WINDOW | PFD_SUPPORT_OPENGL | PFD_DOUBLEBUFFER,
        PFD_TYPE_RGBA,
        24,
        0,0,0,0,0,0,
        0,0,
        0,0,0,0,0,
        32,
        0,
        0,
        PFD_MAIN_PLANE,
        0,
        0,0,0
        };
    PixelFormat = ChoosePixelFormat(hdc, &pfd);
    SetPixelFormat(hdc, PixelFormat, &pfd);
}
//---------------------------------------------------------------------------
void __fastcall TForm3::SetupRC()
{
    glClearColor(1.0f, 0.0f, 0.0f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);
    glFlush();
}
//---------------------------------------------------------------------------
void __fastcall TForm3::RenderScene()
{
    GLfloat x,y,z,angle;
    glClear(GL_COLOR_BUFFER_BIT);
    glPushMatrix();
    glRotatef(90.0f, 1.0f, 0.0f, 0.0f);
    glRotatef(90.0f, 0.0f, 1.0f, 0.0f);
    glBegin(GL_LINE_STRIP);
    z = -20.0f;
    for(angle = 0.0f; angle <= (2.0f * GL_PI) * 3.0f; angle += 0.1f)
    {
        x = 20.0f*sin(angle);
        y = 20.0f*cos(angle);
        glVertex3f(x, y, z);
        z += 0.5f;
    }
    glEnd();
    glPopMatrix();
    glFlush();
}
//---------------------------------------------------------------------------
void __fastcall TForm3::FormPaint(TObject *Sender)
{
    RenderGLScene();
    SwapBuffers(hdc);
   
}
//---------------------------------------------------------------------------
//---------------------------------------------------------------------------
//---------------------------------------------------------------------------