memdc.h

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#ifndef _MEMDC_H_
#define _MEMDC_H_

//////////////////////////////////////////////////
// CMemDC - memory DC
//
// Author: Keith Rule
// Email:  [e-mail]
// 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 {
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, const CRect* pRect = NULL) : CDC()
    {
        ASSERT(pDC != NULL); 

        // Some initialization
        m_pDC = pDC;
        m_oldBitmap = NULL;
        m_bMemDC = !pDC->IsPrinting();

        // Get the rectangle to draw
        if (pRect == NULL) {
            pDC->GetClipBox(&m_rect);
        } else {
            m_rect = *pRect;
        }
        
        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());
    }

    
    ~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