Custom CStatusBar and double-buffering

Hi,

Wondering if anyone has any good ideas here...

I have written a custom CStatusBar control which basically updates
some panes in color as the mouse cursor is moved around. The panes
were flickering due to the amount of redrawing required so I added
some code that uses double-buffering to draw the panes off-screen
first, then blits to screen. I used a well-known piece of code from
Keith Rule on CodeProject in the CMemDC class for this (http://
www.codeproject.com/KB/GDI/flickerfree.aspx?msg=2531592#xx2531592xx).
Here's the code:

<code>
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 accidently 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;
    }
};
</code>

Applying this code requires overriding the OnPaint & OnEraseBkgnd
methods in the custom CStatusBar as follows:

<code>
void MyStatusBar::OnPaint()
{
    CPaintDC dc(this); // device context for painting
    // TODO: Add your message handler code here
    // Do not call CStatusBar::OnPaint() for painting messages
    CRect rect;
    GetClientRect(&rect);
    CMemDC memDC(&dc, &rect);

    DefWindowProc(WM_PAINT, (WPARAM)memDC->m_hDC, (LPARAM)0);
}

BOOL MyStatusBar::OnEraseBkgnd(CDC* pDC)
{
    // TODO: Add your message handler code here and/or call default
    //return CStatusBar::OnEraseBkgnd(pDC);
    return TRUE;

}
</code>

This reduces the flickering, but now the pane borders don't get drawn
at all - they just appear as blank white areas. I have tried
overriding the OnNcPaint function to avoid the call to
CControlBar::EraseNonClient(). No effect. I have also tried calling
DrawBorders explicitly with likewise no effect.

Does anyone have any idea what I'm missing here?

Any suggestions would be much appreciated.

Best,
Bruce