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Flicker Free Drawing In MFC

, 25 Mar 2002 CPOL
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A simple animation example which is used to show CMemDC in several modes

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A simple animation example which is used to show CMemDC in several mode

Introduction

Removing flicker from an MFC application is well-covered territory. You can find the topic addressed in books, and on-line. However, the techniques presented are somewhat complicated and are usually difficult to add to an existing application. One often-presented technique is called double buffering. Double buffering allows the new screen to be drawn in off-screen memory, and then the completed screen is bit-blited back onto the physical screen.

This article presents a class called CMemDC that encapsulates most of the issues associated with writing to off-screen buffers. Adding CMemDC to an existing application or MFC Active X control is nearly trivial.

Modifying an MFC Application to use CMemDC

  • Add the file memdc.h in your project.
  • Add the line #include "memdc.h" to stdafx.h.
  • Add a windows message handler for WM_ERASEBKGND.
  • Change the code in the message handler as follows:
    // Change this code
    BOOL CExampleView::OnEraseBkgnd(CDC* pDC) 
    {
          // TODO: Add your message handler code here and/or call default
          return CView::OnEraseBkgnd(pDC);
    }
     
    // To this code
    BOOL CExampleView::OnEraseBkgnd(CDC* pDC) 
    {
          return FALSE;
    }
  • Change your OnDraw code to the following:
    void CExampleView::OnDraw(CDC* dc)
    {
        CMemDC pDC(dc);
        CExampleDoc* pDoc = GetDocument();
        ASSERT_VALID(pDoc);
        // TODO: add draw code for native data here - use pDC 
         //as the device context to draw to
    }

Compile your code after you've made these changes and you will notice that the flicker you had seen before is gone.

Modifying a MFC Active X Control to use CMemDC

To add CMemDC support you follow the instruction for adding the support to an application, however you make one small change in the OnDraw function.

void CParticleTestCtlCtrl::OnDraw(CDC* pdc, const CRect& rcBounds, 
                                  const CRect& rcInvalid)
{
    CMemDC pDC(pdc, &rcBounds);
    // TODO: add draw code for native data here
    // - use pDC as the device context to draw 
}

The only substantial difference is that the rcBounds is passed to the CMemDC constructor.

Source Code

#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 accidentally 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

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Keith Rule
Software Developer (Senior)
United States United States
I work at Tektronix in Beaverton OR. I've been programming for fun since 1975 (I started while in a Computer Explorer Scout group in Spokane WA). I've been programming in C since 1979 and I've been working professionally since 1983.
 
I really enjoy www.codeproject.com. It has saved me an incredible amount of time. I only hope my small contributions have given back some of what I've taken.

Comments and Discussions

 
Questionstill flickering PinmemberMember 109214303-Jul-14 1:47 
GeneralMy vote of 5 PinmemberMember 1089899126-Jun-14 8:36 
GeneralMy vote of 5 PinmemberWebBiscuit15-Sep-13 12:50 
QuestionIs needed DeleteDC() ? PinmemberJiHyung Lee027-Jan-13 16:36 
QuestionBig Thanks! Pinmembersally Fields5-Nov-12 13:42 
QuestionProblems with CScrollView PinmemberUrbanBlues3-Feb-12 21:48 
AnswerRe: Problems with CScrollView PinmemberAndersBlom29-May-12 23:53 
GeneralMy vote of 5 Pinmember=asm=1-Sep-11 1:24 
QuestionCo-existing with CMemDC from MFC PinmemberJason Steenstra-Pickens19-Apr-11 22:05 
AnswerRe: Co-existing with CMemDC from MFC PinmemberMatrixDud29-Apr-11 10:40 
GeneralRe: Co-existing with CMemDC from MFC PinmemberBen Aldhouse18-Aug-11 22:27 
GeneralMy vote of 5 Pinmemberyiguro13-Jan-11 2:34 
GeneralThanks a lot!!!! Pinmemberyiguro13-Jan-11 2:32 
Man, words can't express how grateful I feel for your article. I have an MFC image manipulating application and it flickered like crazy when modifying brightness using a scroll bar control. Now it looks perfect.
 
Thanks!
GeneralMy vote of 5 Pinmemberbogdan3478-Jan-11 23:57 
GeneralMemory leak after override OnEraseBkgnd method PinmemberPenghui9-Jun-10 7:19 
GeneralCMemDC and scaling paint Pinmembernpuleio2-Feb-10 5:35 
GeneralLicense Concern Pinmemberaitieng31-Jan-10 16:22 
GeneralRe: License Concern PinmemberKeith Rule31-Jan-10 21:11 
QuestionRe: License Concern PinmemberEstelD22-Jun-10 12:14 
AnswerRe: License Concern PinmemberKeith Rule22-Jun-10 12:47 
GeneralRe: License Concern PinmemberEstelD20-Jul-10 9:45 
GeneralOn W7 high cpu usage. Pinmemberspallotti23-Dec-09 6:10 
GeneralSetProcessDefaultLayOut LAYOUT_RTL PinmemberFarid Z27-Oct-09 19:36 
GeneralRe: SetProcessDefaultLayOut LAYOUT_RTL PinmemberPhil Rodgers23-Feb-10 1:57 
GeneralRe: SetProcessDefaultLayOut LAYOUT_RTL [modified] PinmemberFarid Z23-Feb-10 16:15 
NewsMFC Feature Pack for Visual C++ 2008 Pinmembermykel20-Oct-09 8:54 
GeneralRe: MFC Feature Pack for Visual C++ 2008 PinmemberKeith Rule20-Oct-09 11:01 
GeneralRe: MFC Feature Pack for Visual C++ 2008 Pinmembermykel21-Oct-09 1:22 
GeneralRe: MFC Feature Pack for Visual C++ 2008 Pinmembertmpuserz22-Mar-11 13:03 
GeneralRe: MFC Feature Pack for Visual C++ 2008 PinmemberBart10-Jun-11 23:39 
GeneralThanks Pinmemberxsm_12612-Jun-09 22:48 
Answer... PinmemberMember 426330222-Feb-09 21:06 
QuestionCDialog Based application with memdc.h and MSFlexgrid Control Pinmembertmg5128117-Feb-09 4:03 
GeneralThanks~!! PinmemberMember 377536112-Feb-09 15:09 
GeneralVery good job !!! Pinmemberraymondnana29-Jan-09 4:24 
Generalcool... Pinmemberauralius21-Dec-08 19:11 
GeneralCMemDC & Dialog Menu PinmemberSteven Pence8-Dec-08 10:38 
QuestionHow to use in Controls? Pinmemberblamond30-Apr-08 12:14 
AnswerRe: How to use in Controls? Pinmemberblamond6-May-08 9:52 
Generalchild windows Pinmembertoddma9-Nov-07 11:16 
GeneralThanks for some greate time / pain saving! PinmemberSoftwareGeek8-Nov-07 1:08 
GeneralNice work, but... PinmemberSimpleProgrammer15-Aug-07 6:51 
GeneralRe: Nice work, but... Pinmemberbrian.lee5-Sep-07 21:47 
GeneralNot recognising CDC members Pinmemberfacelaunch3-Aug-07 7:53 
QuestionStill flickering Pinmemberfacelaunch3-Aug-07 10:13 
AnswerRe: Still flickering Pinmemberfacelaunch3-Aug-07 10:55 
GeneralRe: Not recognising CDC members PinmemberGuptaP16-Aug-07 9:25 
GeneralRe: Not recognising CDC members PinmemberJDENISW14-Jun-09 9:55 
QuestionDisplay non-solid-color background in scroll-view correctly Pinmemberchen_zd11-Jun-07 3:45 
GeneralThank u. PinmemberMurali_mom30-May-07 22:16 

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