Click here to Skip to main content
14,634,521 members
Articles » Multimedia » GDI » Device Contexts
Article
Posted 20 Nov 1999

Stats

998.1K views
17K downloads
304 bookmarked

Flicker Free Drawing In MFC

Rate this:
4.96 (168 votes)
Please Sign up or sign in to vote.
4.96 (168 votes)
25 Mar 2002CPOL
A simple animation example which is used to show CMemDC in several modes

Sample Image

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 relevant 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)

Share

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

 
GeneralUse with MM_ISOTROPIC Pin
daniel_lidstrom2-May-05 23:08
Memberdaniel_lidstrom2-May-05 23:08 
GeneralRe: Use with MM_ISOTROPIC Pin
parama_chakra19-Jun-05 18:50
Memberparama_chakra19-Jun-05 18:50 
GeneralMemDC's font is not the same! Pin
Fanwy27-Mar-05 15:48
MemberFanwy27-Mar-05 15:48 
GeneralRe: MemDC's font is not the same! Pin
Keith Rule28-Mar-05 8:06
professionalKeith Rule28-Mar-05 8:06 
Questionneed to free memory resource ? Pin
panenhan21-Mar-05 15:59
Memberpanenhan21-Mar-05 15:59 
AnswerRe: need to free memory resource ? Pin
Keith Rule28-Mar-05 8:08
professionalKeith Rule28-Mar-05 8:08 
GeneralDoesn't work for most MM_xxx modes Pin
Vitaly Tomilov15-Mar-05 3:31
MemberVitaly Tomilov15-Mar-05 3:31 
GeneralRe: Doesn't work for most MM_xxx modes Pin
Keith Rule15-Mar-05 6:05
professionalKeith Rule15-Mar-05 6:05 
VitalyTomilov wrote:
The whole approach is failing in alternative Mapping Modes. It only can be used in combination with MM_TEXT. I'm using MM_HIMETRIC, which would imply buffering into a bitmap 100x100=10,000 times larger than for MM_TEXT - there's no such PC to handle a multi-gigabyte bitmap for buffering...

This technique simply encapsulates a standard double buffering scheme into a convenient class. There's nothing special or magic about this approach. And like any approach, it isn't appropriate for all situations. The situation you just described will break any double buffering scheme.

That doesn't mean this approach is broken (it isn't), it just means it's not appropriate for current application.

I'm sorry for your difficulties. Good Luck.


Keith Rule
GeneralDoesn't work with clipped DC Pin
Vitaly Tomilov13-Jan-05 4:39
MemberVitaly Tomilov13-Jan-05 4:39 
QuestionHow does this work with Dialog Based Apps? Pin
Jinegelen30-Nov-04 14:15
MemberJinegelen30-Nov-04 14:15 
GeneralUpdate bug dragging window out of screen Pin
Jesper Knudsen9-Nov-04 2:59
MemberJesper Knudsen9-Nov-04 2:59 
GeneralKeith, thanks ! Pin
andré_k8-Nov-04 0:34
Memberandré_k8-Nov-04 0:34 
Generalonly for very simple drawings Pin
gugul6-Nov-04 4:38
sussgugul6-Nov-04 4:38 
GeneralRe: only for very simple drawings Pin
Keith Rule9-Nov-04 8:05
professionalKeith Rule9-Nov-04 8:05 
GeneralTHNX!!! Pin
mark_sa5-Oct-04 14:20
Membermark_sa5-Oct-04 14:20 
GeneralCListView scrolling issue Pin
s_k2-Oct-04 10:53
Members_k2-Oct-04 10:53 
QuestionLP to DP rounding issue? Pin
Anonymous8-Sep-04 15:07
MemberAnonymous8-Sep-04 15:07 
GeneralNice work! Pin
EpicBoy15-Aug-04 7:40
MemberEpicBoy15-Aug-04 7:40 
GeneralEllipse over Bitmap in mem DC Pin
JackSIL4-Aug-04 8:46
MemberJackSIL4-Aug-04 8:46 
GeneralThankyou! Pin
TheChad11013-Jul-04 7:58
MemberTheChad11013-Jul-04 7:58 
GeneralImplementing a flicker-free CStatic ticker-tape Pin
amit_wtf15-May-04 4:06
sussamit_wtf15-May-04 4:06 
QuestionDoes this work to CFormView? Pin
lily0lin5-May-04 8:35
Memberlily0lin5-May-04 8:35 
Generalunhandled exception Pin
authornet25-Mar-04 10:14
Memberauthornet25-Mar-04 10:14 
GeneralRe: unhandled exception Pin
authornet25-Mar-04 10:30
Memberauthornet25-Mar-04 10:30 
GeneralSetWorldTransform() not compatible with CMemDC Pin
Jason Douglas16-Mar-04 5:05
professionalJason Douglas16-Mar-04 5:05 

General General    News News    Suggestion Suggestion    Question Question    Bug Bug    Answer Answer    Joke Joke    Praise Praise    Rant Rant    Admin Admin   

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.