www.pudn.com > ThumbViewer.rar > memdc.h

#ifndef _MEMDC_H_ 
#define _MEMDC_H_ 
 
////////////////////////////////////////////////// 
// CMemDC - memory DC 
// 
// Author: Keith Rule 
// Email:  keithr@europa.com 
// Copyright 1996-1999, 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. - KR 
// 
//           11/3/99 Fixed most common complaint. Added 
//                   background color fill. - KR 
// 
//           11/3/99 Added support for mapping modes other than 
//                   MM_TEXT as suggested by Lee Sang Hun. - KR 
// 
// This class implements a memory Device Context which allows 
// flicker free drawing. 
 
class CMemDC : public CDC { 
protected: 
   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. 
     
   void Construct(CDC* pDC) 
   { 
        ASSERT(pDC != NULL);  
 
        // Some initialization 
        m_pDC = pDC; 
        m_oldBitmap = NULL; 
        m_bMemDC = !pDC->IsPrinting(); 
 
        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()); 
            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()); 
    } 
 
// TRK begin 
public: 
   CMemDC(CDC* pDC                  ) : CDC() { pDC->GetClipBox(&m_rect); Construct(pDC); } 
   CMemDC(CDC* pDC, const RECT& rect) : CDC() { m_rect = rect           ; Construct(pDC); } 
// TRK end 
     
   virtual ~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