Re: CPaintDC class

From:
Alex Blekhman <xfkt@oohay.moc>
Newsgroups:
microsoft.public.vc.language
Date:
Wed, 04 Oct 2006 13:23:05 +0200
Message-ID:
<OcBU4d65GHA.1188@TK2MSFTNGP05.phx.gbl>
NickP wrote:

Hi there,

    I have some form drawing code that uses the CPaintDC class and it works
fine. But I am just wondering if it is as good as using BeginPaint and
EndPaint.

    I know this class calls these 2 methods anyway, but I am unsure as to
whether it takes in for account the invalid rectangle whilst calling it's
BitBlt method.

    For example, if I declare "CPaintDC dc(myWindowHandle)" and the paint
event args specify that only a small portion of the entire surface is to be
repainted does BitBlt only paint said region?

    ------

    Let's say only the rectangle (100,100,150,150) needs repainting....

    ------

    CPaintDC dc(m_hWnd);
    CRect rc; GetClientRect(&rc);

    //Clear the buffer
    m_memDC.FillRect(&rc,m_bkgrnd);

    //Draw to the buffer here
    ...

    //Blit the buffer
    dc.BitBlt(rc.left,
        rc.top,
        rc.right,
        rc.bottom,
        m_memDC,
        rc.left,
        rc.top,
        SRCCOPY);

    ------

    Does BitBlt actual perform a block copy of the entire rectangle
specified, or only the one that is specified in the paint arguments?


BitBlt is very stupid. It just copies bits from source DC to
destination DC. You can use CPaintDC::m_ps member to figure
out exact paint rectangle.

HTH
Alex

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