memdc.h

visual c++ 实例编程

#if !defined(AFX_MEMDC_H__CA1D3541_7235_11D1_ABBA_00A0243D1382__INCLUDED_)
#define AFX_MEMDC_H__CA1D3541_7235_11D1_ABBA_00A0243D1382__INCLUDED_

#if _MSC_VER >= 1000
#pragma once
#endif // _MSC_VER >= 1000
// MemDC.h : header file
//

//////////////////////////////////////////////////
// CMemDC - memory DC
//
// Author: Keith Rule
// Email:  [e-mail]
// Copyright 1996-1997, Keith Rule
//
// You may freely use or modify this code provided this
// Copyright is included in all derived versions.
//
// History - 10/3/97 Fixed scrolling bug.
//                   Added print support.
//				 12/19/97 - Adrian Roman - Added a constructor that takes two parameters
//				 12/17/99 - TMB! Added the constructor with 2 params (rect) in my version of MemDC.h
//							   This onbe was used with CGridCtrl (derived from CodeGuru ;))
//
// This class implements a memory Device Context

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:
	// Constructor sets up the memory DC
	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
			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;
		}
	}

	CMemDC(CDC* pDC, CRect &rect) : 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();

		m_rect = rect;		// !!

		if (m_bMemDC) {
			// Create a Memory DC
			//pDC->GetClipBox(&m_rect);		// Later...
			CreateCompatibleDC(pDC);
			pDC->GetClipBox(&m_rect);			// Hier dus...
			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;}
};

/////////////////////////////////////////////////////////////////////////////

//{{AFX_INSERT_LOCATION}}
// Microsoft Developer Studio will insert additional declarations immediately before the previous line.

#endif // !defined(AFX_MEMDC_H__CA1D3541_7235_11D1_ABBA_00A0243D1382__INCLUDED_)