Really (or at least more) Flicker Free

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On CodeGuru there are a lot of articles to be found on Flicker Free drawing. The sheer number of articles indicates that none of them is satisfying. Most of the articles and answers suggest to use SetRedraw() on each instance you want to control the drawing (see SomeFunction() below). One drawback of that method is that it doesn't always work. Inserting a column in a list view, for example, seems to ignore the SetRedraw flag. Another drawback is that when your code grows you can't keep track of all those SetRedraw() calls and end up with nested ones that neutralise each other:

void CMyTreeView::SomeFunction()
{
    SetRedraw(FALSE);
    ... do some stuff ...

    SetRedraw(TRUE);
    Invalidate();
}

void CMyTreeView::AnotherFunction()
{
    SetRedraw(FALSE);
    ... do some stuff ...
    SomeFunction();
    ... do more stuff ...  What about the redraw state here?
    SetRedraw(TRUE);
    Invalidate();
}

You get the point. To improve flicker free drawing I do two things: use the SetRedraw() only for the main window of the application and use an internal counter to track nested call and only call SetRedraw() on the first and last occasion of a series.

I implemented it just like CWaitCursor: declare a variable of class CWaitRedraw at the beginning of each function that causes flickering. When the variabele goes out of scope the destructor of CWaitRedraw will be called and handle restoring of the drawing state.

The steps to implement this are as follows:

1. Insert the class CWaitRedraw in your application
2. Put a statement like this at the beginning of each function which causes flickering:
    CWaitRedraw wait;

That's it!

WaitRedraw.h:
/////////////////////////////////////////////////////////////////////
// WaitRedraw.h - class for flicker free drawing
//

#ifndef __WAITREDRAW_H__
#define __WAITREDRAW_H__

#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000

// If not used in a DLL, remove AFX_EXT_CLASS
class AFX_EXT_CLASS CWaitRedraw
{
// Construction/Destruction
public:
    CWaitRedraw();
   ~CWaitRedraw();

// Operations
public:
   void Restore();

protected:
   static int m_nRedrawCount;
};

#endif // __WAITREDRAW_H__

WaitRedraw.cpp:
/////////////////////////////////////////////////////////////////////
// WaitRedraw.cpp - class for flicker free drawing
//
#include "stdafx.h"
#include "WaitRedraw.h"

int CWaitRedraw::m_nRedrawCount = 0;

CWaitRedraw::CWaitRedraw()
{
   CWnd * pMainWnd = AfxGetMainWnd();
   if (pMainWnd)
   {
      if (m_nRedrawCount == 0)
      pMainWnd->SetRedraw(FALSE);
      m_nRedrawCount++;
   }
}

CWaitRedraw::~CWaitRedraw()
{
    CWnd * pMainWnd = AfxGetMainWnd();
    if (pMainWnd)
    {
        if (m_nRedrawCount > 0)

            m_nRedrawCount--;
        if (m_nRedrawCount == 0)
        {
            pMainWnd->SetRedraw(TRUE);
            pMainWnd->Invalidate();
        }
    }
}

// Function to force redrawing
void CWaitRedraw::Restore()
{
   m_nRedrawCount = 0;
   CWnd * pMainWnd = AfxGetMainWnd();
   if (pMainWnd)
   {
      pMainWnd->SetRedraw(TRUE);
      pMainWnd->Invalidate();
   }
}



Download source - 1 KB



Comments

  • CWaitCursor disappears

    Posted by Legacy on 08/05/2002 12:00am

    Originally posted by: Jonathan Taylor

    I have been trying to implement the CWaitRedraw class but each time SetRedraw(FALSE) gets called it resets the CWaitCursor is there anyway round this as it's quite annoying and hindering the usefulness of CWaitRedraw.

    Thanks

    Reply
  • Thoughts

    Posted by Legacy on 11/19/1998 12:00am

    Originally posted by: None

    Any class that omits invalidate window after every call should not
    be called flicker free draw. this is far from flicker free.

    My two cents,
    None

    Reply
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