设置坐标映射模式 为MM_ISOTROPIC后,怎么让区域也随着拖放窗口变化尺寸

坐标映射模式设置为MM_ISOTROPIC, 怎么让区域也随着拖放窗口变化尺寸.
void CRect_TestView::OnDraw(CDC* /*pDC*/)
{
CRect_TestDoc* pDoc = GetDocument();
ASSERT_VALID(pDoc);
if (!pDoc)
return; // TODO: 在此处为本机数据添加绘制代码
CDC * pDC = this->GetDC(); CRect RectClient;
GetClientRect(RectClient);
pDC->SetMapMode(MM_ISOTROPIC);
pDC->SetWindowExt(1000, 1000);
pDC->SetViewportExt(RectClient.right, -RectClient.bottom);
pDC->SetViewportOrg(0, 0);
CRgn Rgn1, Rgn2, Rgn3;
Rgn1.CreateRectRgn(50, 50, 300, 300);
Rgn2.CreateEllipticRgn(50, 50, 300, 300);
Rgn3.CreateRectRgn(0, 0, 400, 400);
Rgn3.CombineRgn(&Rgn1, &Rgn2, RGN_AND); pDC->SelectClipRgn(&Rgn3); CRect Rect(50, -50, 300, -300);
CPen NewPen(PS_SOLID,1, RGB(128,128,128));
CBrush NewBrush1(RGB(255, 0, 0));
CBrush *OldBrush1 = pDC->SelectObject(&NewBrush1);
CPen *OldPen = pDC->SelectObject(&NewPen);

pDC->Rectangle(0, 0, 600, -600);
pDC->SelectObject(OldBrush1); this->ReleaseDC(pDC);
}