www.pudn.com > NetPaw.rar > MemDC.h

#ifndef _MEMDC_H_ 
#define _MEMDC_H_ 
 
//*******************************************************************************************************/ 
//* Class:			CMemDC - memory DC 
//* 
//* Base Class:		public CDC 
//* 
//* Description:	This class implements a memory Device Context that enables flicker free drawing. 
//* 
//* Usage:			Implemen CMemDC in your CMyWnd::OnPaint as following: 
//*					{ 
//*						CPaintDC	dc(pWnd); 
//*						CMemDC		mDC(&dc);	// call CMemDC::CMemDC(CDC *dc) 
//* 
//*						Draw(&mDC);				// draw on CMemDC rather than CDC directly. 
//*					}							// call CMemDC::~CMemDC() 
//* 
//*					Finally, add and modify WM_ERASEBKGND message in your project as following: 
//*					BOOL CMyView::OnEraseBkgnd(CDC* pDC)  
//*					{ 
//*						return FALSE; 
//*					} 
//* 
//* 
//* 10/3/97		Keith Rule			Fixed scrolling bug. 
//* 10/3/97		Keith Rule			Added print support. 
//* 12.feb.98	Jan Vidar Berger	Ported CMemDC into clPlot and added some comments. 
//* 
//*******************************************************************************************************/ 
 
class CMemDC : public CDC 
{ 
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. 
 
public: 
	CMemDC(CDC* pDC) : CDC(), m_pOldBitmap(NULL), m_pDC(pDC) 
	{ 
		ASSERT(m_pDC != NULL);			// If you asserted here, you passed in a NULL CDC. 
 
		m_bMemDC = !pDC->IsPrinting(); 
 
		if (m_bMemDC) 
		{ 
			// Create a Memory DC 
			CreateCompatibleDC(pDC); 
			pDC->GetClipBox(&m_Rect); 
			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; 
		} 
	} 
 
	~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); 
 
			// Restore old 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;} 
}; 
 
#endif