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BOOL CDlg::OnEraseBkgnd(CDC* pDC)
{
// TODO: 在此添加消息处理程序代码和/或调用默认值
return FALSE;//CDialogEx::OnEraseBkgnd(pDC);
}
void CDlg::OnPaint()
{
CPaintDC dc(this); // device context for painting
// TODO: 在此处添加消息处理程序代码
// 不为绘图消息调用 CDialogEx::OnPaint()
CRect rct;
GetClientRect(&rct);
CMemDC memDC(dc, rct);
CDC *pDC = &memDC.GetDC();
//填充背景色
pDC->FillSolidRect(&rct, RGB(100, 100, 100));
}
class CMemDC : public CDC
{
public:
// constructor sets up the memory DC
CMemDC(CDC* pDC) : CDC()
{
ASSERT(pDC != NULL);
m_pDC = pDC;
m_pOldBitmap = NULL;
m_bMemDC = !pDC->IsPrinting();
if (m_bMemDC) // Create a Memory DC
{
pDC->GetClipBox(&m_rect);
CreateCompatibleDC(pDC);
m_bitmap.CreateCompatibleBitmap(pDC, m_rect.Width(), m_rect.Height());
m_pOldBitmap = SelectObject(&m_bitmap);
SetWindowOrg(m_rect.left, m_rect.top);
}
else // Make a copy of the relevent parts of the current DC for printing
{
m_bPrinting = pDC->m_bPrinting;
m_hDC = pDC->m_hDC;
m_hAttribDC = pDC->m_hAttribDC;
}
}
// Destructor copies the contents of the mem DC to the original DC
~CMemDC()
{
if (m_bMemDC)
{
// Copy the offscreen bitmap onto the screen.
m_pDC->BitBlt(m_rect.left, m_rect.top, m_rect.Width(), m_rect.Height(),
this, m_rect.left, m_rect.top, SRCCOPY);
//Swap back the original bitmap.
SelectObject(m_pOldBitmap);
} else {
// All we need to do is replace the DC with an illegal value,
// this keeps us from accidently deleting the handles associated with
// the CDC that was passed to the constructor.
m_hDC = m_hAttribDC = NULL;
}
}
// Allow usage as a pointer
CMemDC* operator->() {return this;}
// Allow usage as a pointer
operator CMemDC*() {return this;}
private:
CBitmap m_bitmap; // Offscreen bitmap
CBitmap* m_pOldBitmap; // bitmap originally found in CMemDC
CDC* m_pDC; // Saves CDC passed in constructor
CRect m_rect; // Rectangle of drawing area.
BOOL m_bMemDC; // TRUE if CDC really is a Memory DC.
};