请教：OpenGL 画圆柱始终是椭圆形的

问题：
我现在利用OpenGL画圆，窗口像素为450x300时画出的圆的形状为椭圆，不知如何设置让他为圆形的？
如果窗口的宽，高的比例为1:1时，即窗口像素为300x300时，圆的形状为圆形的。

代码如下：



/////////////////////////////////////////////////////////////////////////////
// COpenGLDlg message handlers

BOOL COpenGLDlg::OnInitDialog()
{
CDialog::OnInitDialog();

// TODO: Add extra initialization here
this->MoveWindow(570,80,450,300,TRUE);

glInitOGLES();

return TRUE; // return TRUE unless you set the focus to a control
// EXCEPTION: OCX Property Pages should return FALSE
}


void COpenGLDlg::OnDestroy()
{
CDialog::OnDestroy();

// TODO: Add your message handler code here
if(wglGetCurrentContext()!=NULL)
{
wglMakeCurrent(NULL,NULL);
}

if(m_hGLContext!=NULL)
{
wglDeleteContext(m_hGLContext);
m_hGLContext=NULL;
}
}

//创建OpenGL绘制描述表
BOOL COpenGLDlg::glInitOGLES()
{
PIXELFORMATDESCRIPTOR pfd;
int n;
HGLRC hrc;

m_pDC = new CClientDC(this);

ASSERT(m_pDC != NULL);

if (!SetupPixelFormat())
return FALSE;

n =::GetPixelFormat(m_pDC->GetSafeHdc());
::DescribePixelFormat(m_pDC->GetSafeHdc(), n, sizeof(pfd), &pfd);

hrc = wglCreateContext(m_pDC->GetSafeHdc());
wglMakeCurrent(m_pDC->GetSafeHdc(), hrc);


glClearDepth(1.0f); // 设置深度缓存
glEnable(GL_DEPTH_TEST); // 启用深度测试
glDepthFunc(GL_LEQUAL); // 所作深度测试的类型
glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);


return TRUE;
}

//设置像数格式
BOOL COpenGLDlg::SetupPixelFormat()
{
static 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
};
int pixelformat;

if ( (pixelformat = ChoosePixelFormat(m_pDC->GetSafeHdc(), &pfd)) == 0 )
{
MessageBox("ChoosePixelFormat failed");
return FALSE;
}

if (SetPixelFormat(m_pDC->GetSafeHdc(), pixelformat, &pfd) == FALSE)
{
MessageBox("SetPixelFormat failed");
return FALSE;
}

return TRUE;
}

//初始化视模式
void COpenGLDlg::glInitViewModel(int x,int y)
{

// GetClientRect(&m_oldRect);

// glClearDepth(1.0f); // 设置深度缓存
// glEnable(GL_DEPTH_TEST); // 启用深度测试
// glDepthFunc(GL_LEQUAL); // 所作深度测试的类型

/* glViewport(0, 0, x, y); //设置视口

glMatrixMode(GL_PROJECTION); // 选择投影矩阵
glLoadIdentity();
//gluPerspective(45.0f,(GLfloat)m_oldRect.right/(GLfloat)m_oldRect.bottom,0.1f,100.0f);

glOrtho(0,0,x,y,0.1f,100.0f);

// gluPerspective(45.0f,1.5,0.1f,100.0f);

glMatrixMode(GL_MODELVIEW); // 选择模型观察矩阵
glLoadIdentity();
// glViewport(0, 0, 450, 300); //设置视口

// gluLookAt(0.0,0.0,100.0,0.0,0.0,0.0,0.0,1.0,0.0);*/

GLfloat nRange=1.0f;
//避免除数为0
if(y==0)
y=1;

//设置视口与窗口匹配
glViewport(0,0,x,y);

//重新设置坐标系统
glMatrixMode(GL_PROJECTION);
glLoadIdentity();

//建立正交变换下的剪切体
if(x<y)
glOrtho(-nRange,nRange,-nRange*y/x,nRange*y/x,-nRange,nRange);
else
glOrtho(-nRange*y/x,nRange*y/x,-nRange,nRange,-nRange,nRange);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();



// glClearDepth(1.0f); // 设置深度缓存
// glEnable(GL_DEPTH_TEST); // 启用深度测试
// glDepthFunc(GL_LEQUAL); // 所作深度测试的类型
// glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);


// glClearColor(0.1f,0.4f,0.5f,1.0f);
// glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
}


//设置灯光
void COpenGLDlg::glSetLight()
{
GLfloat light0Ambient[]={0.3f,0.8f,0.5f,1.0f}; // 环境光参数
GLfloat light0Diffuse[]={0.9f,0.9f,0.9f,1.0f};
GLfloat light0Position[]={1.0f,2.0f,2.0f,0.0f}; // 设置光源位置

glLightfv(GL_LIGHT0,GL_AMBIENT,light0Ambient);
glLightfv(GL_LIGHT0,GL_DIFFUSE,light0Diffuse);
glLightfv(GL_LIGHT0,GL_POSITION,light0Position);

glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);

// glEnable(GL_DEPTH_TEST);
// glEnable(GL_CULL_FACE);
}

void COpenGLDlg::RenderScene()
{
glClearColor(0.1f,0.4f,0.5f,1.0f); //以固定的颜色设置背景
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // 清除屏幕和深度缓存
//glLoadIdentity(); // 重置当前的模型观察矩阵


glSetLight(); //设置光照

glColor4f(1.0,0.0,0.2,0.1);

glLineWidth(1);

glBegin(GL_LINES);
glVertex2f(0.0f,-1.0f);
glVertex2f(0.0f,1.0f);
glEnd();

glBegin(GL_LINES);
glVertex2f(1.0f,0.0f);
glVertex2f(-1.0f,0.0f);
glEnd();

GLUquadricObj* quadObj;
quadObj=gluNewQuadric();
gluQuadricDrawStyle(quadObj,GLU_FILL);
gluQuadricOrientation(quadObj,GLU_OUTSIDE);
gluQuadricNormals(quadObj,GLU_SMOOTH);

double ra=0.2;
double k=ra/m_dbRa;
double rb=k*m_dbRb;
double rc=k*m_dbRc;
double rd=k*m_dbRd;



glPushMatrix();

glTranslatef (0.0, 0.0, 0.0); //视点变换
glRotatef(10.0,0.0f,1.0f,0.0f);
gluCylinder(quadObj,0.2,0.2,50,30,30);

gluDisk(quadObj,0.0,0.2,30,30);
glPopMatrix();

glPushMatrix();

glTranslatef (0.0, 0.0, 0.0); //视点变换
glTranslatef (0.0, -(ra+rb), 0.0); //视点变换
glRotatef(10.0,0.0f,1.0f,0.0f);

gluCylinder(quadObj,rb,rb,50,30,30);
gluDisk(quadObj,0.0,rb,30,30);
glPopMatrix();


glPushMatrix();
glTranslatef (0.0, 0.0, 0.0); //视点变换
glTranslatef (0.6, 0.0, 0.0); //视点变换
glRotatef(10.0,0.0f,1.0f,0.0f);
gluCylinder(quadObj,0.1,0.1,50,30,30);
//gluDisk(quadObj,0.0,0.1,30,30);
glPopMatrix();

/* GLUquadricObj* quadObj;
quadObj=gluNewQuadric();
gluQuadricDrawStyle(quadObj,GLU_FILL);
gluQuadricOrientation(quadObj,GLU_OUTSIDE);
gluQuadricNormals(quadObj,GLU_SMOOTH);

GLfloat cy1_amb_dif[]={0.0f,1.0f,0.0f,1.0f};
GLfloat cy1_spec[]={1.0f,1.0f,1.0f,1.0f};

GLfloat sph_amb_dif[]={0.0f,1.0f,0.0f,1.0f};
GLfloat sph_spec[]={1.0f,1.0f,1.0f,1.0f};


glRotatef(10.0,0.0f,1.0f,0.0f);

glRotatef(6.0,0.0f,0.0f,1.0f);


// GLuint cy1=glGenLists(1);
// glNewList(cy1,GL_COMPILE);
// glMaterialfv(GL_FRONT,GL_AMBIENT_AND_DIFFUSE,cy1_amb_dif);
// glMaterialfv(GL_FRONT,GL_SPECULAR,cy1_spec);
// glMaterialf(GL_FRONT,GL_SHININESS,100.0);
// gluCylinder(quadObj,0.5,0.5,100.0,50,50);
// glEndList();*/


glFinish();
SwapBuffers(wglGetCurrentDC());
//glDrawBuffer(GL_FRONT);
}



void COpenGLDlg::OnPaint()
{
CPaintDC dc(this); // device context for painting

// TODO: Add your message handler code here
RenderScene();

// Do not call CDialog::OnPaint() for painting messages
}


void COpenGLDlg::OnSize(UINT nType, int cx, int cy)
{
CDialog::OnSize(nType, cx, cy);

// TODO: Add your message handler code here
glInitViewModel(cx,cy);

}