为什么StretchBlt缩放后成了这个样子,该如何处理

为什么StretchBlt缩放后成了这个样子
在内存中画图，然后用StretchBlt画到picturebox上，怎么缩放后有一部分没出来，button1代码如下：
[code=C/C++][/code] CDC* pDC = GetDlgItem(IDC_STATIC)->GetDC();
CDC memDC;
memDC.CreateCompatibleDC(pDC);
CRect RectPicturebox;
GetDlgItem(IDC_STATIC)->GetClientRect(&RectPicturebox);
CBitmap bmp;
bmp.CreateCompatibleBitmap(pDC,RectPicturebox.Width(),RectPicturebox.Height());
CBitmap *pOldbmp = memDC.SelectObject(&bmp);
CRect rect;
rect.bottom = 400;
rect.top = 0;
rect.left = 0;
rect.right = 400;
memDC.Ellipse(&rect);
pDC->SetStretchBltMode(STRETCH_HALFTONE | STRETCH_ORSCANS);
pDC->StretchBlt(0,0,RectPicturebox.Width(),RectPicturebox.Height(),&memDC,0,0,rect.Width(),rect.Height(),SRCCOPY);



------解决方案--------------------
CRect rect;
 rect.bottom = 400;
 rect.top = 0;
 rect.left = 0;
 rect.right = 400;
你这里的400,400是图片的大小码？
------解决方案--------------------

C/C++ code

CDC* pDC = GetDlgItem(IDC_STATIC1)->GetDC();
 CDC memDC;
 memDC.CreateCompatibleDC(pDC);
 CRect RectPicturebox;
 GetDlgItem(IDC_STATIC1)->GetClientRect(&RectPicturebox);
 CBitmap bmp;
 bmp.CreateCompatibleBitmap(pDC,RectPicturebox.Width(),RectPicturebox.Height());
 CBitmap *pOldbmp = memDC.SelectObject(&bmp);
 CRect rect;
 rect.bottom = RectPicturebox.Height();
 rect.top = 0;
 rect.left = 0;
 rect.right = RectPicturebox.Width();
 memDC.Ellipse(&rect);
 pDC->SetStretchBltMode(STRETCH_HALFTONE | STRETCH_ORSCANS);
 pDC->StretchBlt(0,0,RectPicturebox.Width(),RectPicturebox.Height(),&memDC,0,0,rect.Width(),rect.Height(),SRCCOPY);
 memDC.SelectObject(pOldbmp);
 memDC.DeleteDC();
 GetDlgItem(IDC_STATIC1)->ReleaseDC(pDC);