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MemDC.h
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Upload Date: 2013-01-26
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Code Size: 4k
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Graph Drawing

Development Platform:

Visual C++

MemDC.h：Code Content
  1. //*******************************************************************************************************/
  2. //* FileName: MemDC.h
  3. //*
  4. //* Contents: Definition and implementation for CMemDC
  5. //*
  6. //* Copyright You may freely use or modify this code provided this Copyright is included in all 
  7. //* Notice: derived versions.
  8. //*
  9. //* Author: Keith Rule
  10. //*
  11. //* Email: keithr@europa.com
  12. //*
  13. //* Copyright 1996-1997, Keith Rule
  14. //*******************************************************************************************************/
  15. //* 10/3/97 Keith Rule Fixed scrolling bug.
  16. //* 10/3/97 Keith Rule Added print support.
  17. //* 12.feb.98 Jan Vidar Berger Ported CMemDC into clPlot and added some comments.
  18. //*******************************************************************************************************/
  19. #ifndef _MEMDC_H_
  20. #define _MEMDC_H_
  23. //*******************************************************************************************************/
  24. //* Class: CMemDC - memory DC
  25. //*
  26. //* Base Class: public CDC
  27. //*
  28. //* Description: This class implements a memory Device Context that enables flicker free drawing.
  29. //*
  30. //* Usage: Implemen CMemDC in your CMyWnd::OnPaint as following:
  31. //* {
  32. //* CPaintDC dc(pWnd);
  33. //* CMemDC mDC(dc); // call CMemDC::CMemDC(CDC *dc)
  34. //*
  35. //* Draw(mDC); // draw on CMemDC rather than CDC directly.
  36. //* } // call CMemDC::~CMemDC()
  37. //*
  38. //* Finally, add and modify WM_ERASEBKGND message in your project as following.
  39. //*
  40. //* BOOL CMyView::OnEraseBkgnd(CDC* pDC) 
  41. //* {
  42. //* return FALSE;
  43. //* }
  44. //*
  45. //* How it works: 1. The constructor will construct compatibledc and do the work required to enable 
  46. //* drawing on a memory dc.
  47. //* 2. You can draw on the CMemDC as if it is a CDC.
  48. //* 3. The destructor copies the memory dc into the real DC.
  49. //*******************************************************************************************************/
  50. class CMemDC : public CDC {
  51. private:
  52.         CBitmap m_bitmap; // Offscreen bitmap
  53.         CBitmap* m_oldBitmap; // bitmap originally found in CMemDC
  54.         CDC* m_pDC; // Saves CDC passed in constructor
  55.         CRect m_rect; // Rectangle of drawing area.
  56.         BOOL m_bMemDC; // TRUE if CDC really is a Memory DC.
  57. public:
  58.         CMemDC(CDC* pDC) : CDC(), m_oldBitmap(NULL), m_pDC(pDC)
  59.         {
  60.                 ASSERT(m_pDC != NULL); // If you asserted here, you passed in a NULL CDC.
  61.                 
  62.                 m_bMemDC = !pDC->IsPrinting();
  63.                 
  64.                 if (m_bMemDC){
  65.                         // Create a Memory DC
  66.                         CreateCompatibleDC(pDC);
  67.                         pDC->GetClipBox(&m_rect);
  68.                         m_bitmap.CreateCompatibleBitmap(pDC, m_rect.Width(), m_rect.Height());
  69.                         m_oldBitmap = SelectObject(&m_bitmap);
  70.                         SetWindowOrg(m_rect.left, m_rect.top);
  71.                 } else {
  72.                         // Make a copy of the relevent parts of the current DC for printing
  73.                         m_bPrinting = pDC->m_bPrinting;
  74.                         m_hDC = pDC->m_hDC;
  75.                         m_hAttribDC = pDC->m_hAttribDC;
  76.                 }
  77.         }
  78.         
  79.         ~CMemDC()
  80.         {
  81.                 if (m_bMemDC) {
  82.                         // Copy the offscreen bitmap onto the screen.
  83.                         m_pDC->BitBlt(m_rect.left, m_rect.top, m_rect.Width(), m_rect.Height(),
  84.                                 this, m_rect.left, m_rect.top, SRCCOPY);
  85.                         //Swap back the original bitmap.
  86.                         SelectObject(m_oldBitmap);
  87.                 } else {
  88.                         // All we need to do is replace the DC with an illegal value,
  89.                         // this keeps us from accidently deleting the handles associated with
  90.                         // the CDC that was passed to the constructor.
  91.                         m_hDC = m_hAttribDC = NULL;
  92.                 }
  93.         }
  94.         
  95.         // Allow usage as a pointer
  96.         CMemDC* operator->() {return this;}
  97.         
  98.         // Allow usage as a pointer
  99.         operator CMemDC*() {return this;}
  100. };
  102. #endif