OpenGl写个动画为何会卡住？急求！！！！！！！！！！！！！！！！！

void CMFCopengl2Dlg::draw1(){
CPaintDC dc1(this);
do
{
Sleep(50);
glBegin(GL_LINE_STRIP);
glColor3f(0.0, 0.7, 1.0);
glVertex2f(510, 400);
glVertex2f(510, 400 - i);
i = i + 10;
glEnd();
//dwEnd = GetTickCount() - dwStart;
glFlush();
SwapBuffers(dc1);
} while (i < 200);

}

shader问题?有木有报错之类的啊.