memdc.h

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#ifndef _MEMDC_H_
#define _MEMDC_H_

// CMemDC - memory DC
//
// Author: Keith Rule
// Email:  keithr@europa.com
// Copyright 1996-2002, 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
//
//           02/11/02 Added support for CScrollView as supplied
//                    by Gary Kirkham. - 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());

                        SetWindowExt(pDC->GetWindowExt());
                        SetViewportExt(pDC->GetViewportExt());

                        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