坐标变换之后出现问题！！！

Question

上边贴错
极坐标的时候是
    RECT rect;
        GetClientRect(&rect);
        pDC->SetMapMode(MM_ANISOTROPIC);
    pDC->SetViewportOrg(rect.right/2,rect.bottom/2);
    pDC->SetViewportExt(rect.right,rect.bottom);
    pDC->SetWindowOrg(0,0);
    pDC->SetWindowExt(1000,-1000);
    pDC->MoveTo(0,500);
        pDC->LineTo(0,-500);
        pDC->MoveTo(-500,0);
        pDC->LineTo(500,0);
        double x=200*cos(30*3.14/180),y=200*sin(30*3.14/180);
           //double to  int !!!这里严重失真，怎么解决？
        pDC->Ellipse(-x,y,x,-y);  //参数一定是 int
这样