CMemDC.h

#ifndef _MEMDC_H_
#define _MEMDC_H_

//////////////////////////////////////////////////
// CMemDC - memory DC
//
// Author: Keith Rule
// Email:  keithr@europa.com
// 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.
//
// This class implements a memory Device Context

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, CRect* rect)
    : CDC(), m_oldBitmap(NULL), m_pDC(pDC), m_rect(*rect)
  {
    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