class CMemDC : public CDC {
private:
CBitmap m_bitmap;
CBitmap* m_oldBitmap;
CDC* m_pDC;
CRect m_rect;
BOOL m_bMemDC;
public:
CMemDC(CDC* pDC, const CRect* pRect = NULL);
~CMemDC();
// Allow usage as a pointer
CMemDC* operator->();
// Allow usage as a pointer
operator CMemDC*();
};
CMemDC::CMemDC(CDC* pDC, const CRect* pRect) : CDC()
{
ASSERT(pDC != NULL);
// Some initialization
m_pDC = pDC;
m_oldBitmap = NULL;
m_bMemDC = !pDC->IsPrinting();
// Get the rectangle to draw
if (pRect == NULL)
{
pDC->GetClipBox(&m_rect);
}
else
{
m_rect = *pRect;
}
if (m_bMemDC)
{
// Create a Memory DC
CreateCompatibleDC(pDC);
pDC->LPtoDP(&m_rect);
m_bitmap.CreateCompatibleBitmap(pDC, m_rect.Width(),m_rect.Height());
m_oldBitmap = SelectObject(&m_bitmap);
SetMapMode(pDC->GetMapMode());
SetWindowExt(pDC->GetWindowExt());
SetViewportExt(pDC->GetViewportExt());
pDC->DPtoLP(&m_rect);
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;
}
// Fill background
FillSolidRect(m_rect, pDC->GetBkColor());
}
CMemDC::~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_oldBitmap);
}
else
{
// All we need to do is replace the DC with an illegal
// value, this keeps us from accidentally deleting the
// handles associated with the CDC that was passed to
// the constructor.
m_hDC = m_hAttribDC = NULL;
}
}
CMemDC*
CMemDC::operator->()
{
return this;
}
CMemDC::operator CMemDC*()
{
return this;
}