// MemDC.h : header file

#include "StdAfx.h"

#pragma once

class CMemDC_Redefine : public CDC
{
public:
	
	//构造内存设备场景
	CMemDC_Redefine(CDC* pDC) : CDC()
	{
		ASSERT(pDC != NULL);

		m_pDC = pDC;
		m_pOldBitmap = NULL;
		m_bMemDC = !pDC->IsPrinting();

		if (m_bMemDC)
		{
			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	
		{
			m_bPrinting = pDC->m_bPrinting;
			m_hDC		= pDC->m_hDC;
			m_hAttribDC = pDC->m_hAttribDC;
		}
	}
	
	//析构
	~CMemDC_Redefine()
	{
		if (m_bMemDC)
		{	
			m_pDC->BitBlt(m_rect.left, m_rect.top, m_rect.Width(), m_rect.Height(),
				this, m_rect.left, m_rect.top, SRCCOPY);

			SelectObject(m_pOldBitmap);
		} 
		else 
		{
			m_hDC = m_hAttribDC = NULL;
		}
	}

	CMemDC_Redefine * operator->() 
	{
		return this;
	}

	operator CMemDC_Redefine *()
	{
		return this;
	}

private:
	CBitmap  m_bitmap;		
    CBitmap* m_pOldBitmap;	
    CDC*     m_pDC;		
    CRect    m_rect;		
    BOOL     m_bMemDC;		
};