CBrush backBrush(RGB(221, 221, 221)); //改变后的背景色
// Save old brush
CBrush* pOldBrush = pDC->SelectObject(&backBrush);
CRect rect;
pDC->GetClipBox(&rect); // Erase the area needed
pDC->PatBlt(rect.left, rect.top, rect.Width(), rect.Height(),
PATCOPY);
pDC->SelectObject(pOldBrush);