Further discussions on flicker free drawing

Introduction

This article aims to show some useful codes for solving flicker problems in CTreeCtrl, CListCtrl and GDI+. And it could be viewed as an extend of Keith Rule's great article "Flicker Free Drawing In MFC".

Background

The only background to this article is that you have read the great article of Keith Rule. Thanks him for his nice code. We will use the class CMemDC proposed by him.

CTreeCtrl

For a CTreeCtrl derived class, if we want to avoid flicker, we could carry out the following steps.

• Add the file memdc.h in your project.
• Add the line #include "memdc.h" to stdafx.h or the desired .h file.
• Add a public CRect variable like CRect m_rectClient;
• Add a windows message handler for WM_ERASEBKGND, WM_SIZE, and WM_PAINT.

Then we should add the code as following:

BOOL CTreeCtrl::OnEraseBkgnd(CDC* pDC) 
{
    // TODO: Add your message handler code here and/or call default
    UNUSED_ALWAYS(pDC);

    //return CTreeCtrl::OnEraseBkgnd(pDC);
    return TRUE;
}

void CTreeCtrl::OnSize(UINT nType, int cx, int cy) 
{
    CTreeCtrl::OnSize(nType, cx, cy);

    GetClientRect(m_rectClient);
}

void CTreeCtrl::OnPaint() 
{
    CPaintDC dc(this);

    // Paint to a memory device context to reduce screen flicker.
    CMemDC memDC(&dc, &m_rectClient);

    ......

    // Let the window do its default painting...
    CWnd::DefWindowProc( WM_PAINT, (WPARAM)memDC.m_hDC, 0 );
}

Then you would get flicker free effect.

CListCtrl

For a CListCtrl derived class, all of the procedures are the same expect the OnSize function should be modified as following to allow the CHeadCtrl (if in report model) to display:

void CListCtrl::OnSize(UINT nType, int cx, int cy) 
{
    CListCtrl::OnSize(nType, cx, cy);

    GetClientRect(m_rectClient);

    CHeaderCtrl* pHC;
    pHC = GetHeaderCtrl();
    if (pHC != NULL)
    {
        CRect rectHeader;
        pHC->GetItemRect( 0, &rectHeader );
        m_rectClient.top += rectHeader.bottom;
    }
}

Then you could get flicker free effect.

GDI+

I have found several articles talking about flicker free drawing in GDI+. However, I want to extend Keith Rule's code to do the same job and avoid to re-implement the double buffer mechanism with CashedBitmap. Thus I use the following method.

• Add the file memdc.h in your project.
• Add the line #include "memdc.h" to stdafx.h or the desired .h file.
• Add a public CRect variable likeCRect m_rectClient; Add a windows message handler for WM_ERASEBKGND, WM_SIZE, and WM_PAINT.

Then we should add the code as following:

BOOL CView::OnEraseBkgnd(CDC* pDC) 
{
    // TODO: Add your message handler code here and/or call default
    UNUSED_ALWAYS(pDC);

    //return CView::OnEraseBkgnd(pDC);
    return TRUE;
}

void CView::OnSize(UINT nType, int cx, int cy) 
{
    CView::OnSize(nType, cx, cy);

    GetClientRect(m_rectClient);
}

void CView::OnPaint() 
{
    CPaintDC dc(this);

    // Paint to a memory device context to reduce screen flicker.
    CMemDC memDC(&dc, &m_rectClient);
    Graphics graphics(memDC);

    ......
}

Then you could get flicker free effect. This method could also do well in CScrollView. Ok, finally, there is still an interesting question left for you: which method will be faster, this method or the double buffer implemented by CashedBitmap?

History

• Initial release 2003-05-24.