C / C++ / MFC

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class CMemDC : public CDC {<br />
private:<br />
        CBitmap         m_bitmap;               // Offscreen bitmap<br />
        CBitmap*        m_oldBitmap;    // bitmap originally found in CMemDC<br />
        CDC*            m_pDC;                  // Saves CDC passed in constructor<br />
        CRect           m_rect;                 // Rectangle of drawing area.<br />
        BOOL            m_bMemDC;               // TRUE if CDC really is a Memory DC.<br />
public:<br />
<br />
        CMemDC(CDC* pDC, const CRect* pRect = NULL) : CDC()<br />
        {<br />
                ASSERT(pDC != NULL);<br />
<br />
                // Some initialization<br />
                m_pDC = pDC;<br />
                m_oldBitmap = NULL;<br />
                m_bMemDC = !pDC->IsPrinting();<br />
<br />
                // Get the rectangle to draw<br />
                if (pRect == NULL) {<br />
                        pDC->GetClipBox(&m_rect);<br />
                } else {<br />
                        m_rect = *pRect;<br />
                }<br />
<br />
                if (m_bMemDC) {<br />
                        // Create a Memory DC<br />
                        CreateCompatibleDC(pDC);<br />
                        pDC->LPtoDP(&m_rect);<br />
<br />
                        m_bitmap.CreateCompatibleBitmap(pDC, m_rect.Width(),<br />
m_rect.Height());<br />
                        m_oldBitmap = SelectObject(&m_bitmap);<br />
<br />
                        SetMapMode(pDC->GetMapMode());<br />
<br />
                        SetWindowExt(pDC->GetWindowExt());<br />
                        SetViewportExt(pDC->GetViewportExt());<br />
<br />
                        pDC->DPtoLP(&m_rect);<br />
                        SetWindowOrg(m_rect.left, m_rect.top);<br />
                } else {<br />
                        // Make a copy of the relevent parts of the current DC for printing<br />
                        m_bPrinting = pDC->m_bPrinting;<br />
                        m_hDC       = pDC->m_hDC;<br />
                        m_hAttribDC = pDC->m_hAttribDC;<br />
                }<br />
<br />
                // Fill background<br />
                FillSolidRect(m_rect, pDC->GetBkColor());<br />
        }<br />
<br />
        ~CMemDC()<br />
        {<br />
                if (m_bMemDC) {<br />
                        // Copy the offscreen bitmap onto the screen.<br />
                        m_pDC->BitBlt(m_rect.left, m_rect.top, m_rect.Width(),<br />
m_rect.Height(),<br />
                                this, m_rect.left, m_rect.top, SRCCOPY);<br />
<br />
                        //Swap back the original bitmap.<br />
                        SelectObject(m_oldBitmap);<br />
                } else {<br />
                        // All we need to do is replace the DC with an illegal value,<br />
                        // this keeps us from accidently deleting the handles associated<br />
with<br />
                        // the CDC that was passed to the constructor.<br />
                        m_hDC = m_hAttribDC = NULL;<br />
                }<br />
        }<br />
<br />
        // Allow usage as a pointer<br />
        CMemDC* operator->()<br />
        {<br />
                return this;<br />
        }<br />
<br />
        // Allow usage as a pointer<br />
        operator CMemDC*()<br />
        {<br />
                return this;<br />
        }<br />
};<br />

<br />
void MyStatusBar::OnPaint()<br />
{<br />
        CPaintDC dc(this); // device context for painting<br />
        // TODO: Add your message handler code here<br />
        // Do not call CStatusBar::OnPaint() for painting messages<br />
        CRect rect;<br />
        GetClientRect(&rect);<br />
        CMemDC memDC(&dc, &rect);<br />
<br />
        DefWindowProc(WM_PAINT, (WPARAM)memDC->m_hDC, (LPARAM)0);<br />
<br />
}<br />
<br />
BOOL MyStatusBar::OnEraseBkgnd(CDC* pDC)<br />
{<br />
        // TODO: Add your message handler code here and/or call default<br />
        //return CStatusBar::OnEraseBkgnd(pDC);<br />
        return TRUE;<br />
<br />
}<br />
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