memdc.h

一个网络监视的程序

//*******************************************************************************************************/
//* FileName:		MemDC.h
//*
//* Contents:		Definition and implementation for CMemDC
//*
//* Copyright		You may freely use or modify this code provided this Copyright is included in all 
//* Notice:			derived versions.
//*
//* Author:			Keith Rule
//*
//* Email:			[e-mail]
//*
//* Copyright 1996-1997, Keith Rule
//*******************************************************************************************************/
//* 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.
//*******************************************************************************************************/
#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;
//*					}
//*
//* How it works:	1.	The constructor will construct compatibledc and do the work required to enable 
//*						drawing on a memory dc.
//*					2.	You can draw on the CMemDC as if it is a CDC.
//*					3.	The destructor copies the memory dc into the real DC.
//*******************************************************************************************************/
class CMemDC : public CDC {
private:
        CBitmap m_bitmap;								// Offscreen bitmap
        CBitmap* m_oldBitmap;							// 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_oldBitmap(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_oldBitmap = 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);
                        //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 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