From kde-core-devel  Fri Mar 13 16:51:11 2009
From: Hans Meine <hans_meine () gmx ! net>
Date: Fri, 13 Mar 2009 16:51:11 +0000
To: kde-core-devel
Subject: Re: KIO::PreviewJob pixmaps + Qt4.5 crashes
Message-Id: <200903131751.13186.hans_meine () gmx ! net>
X-MARC-Message: https://marc.info/?l=kde-core-devel&m=123696316010846

On Friday 13 March 2009 15:14:33 Aleix Pol wrote:
> > #3) The other response is likely right. I bet the following accesses
> > deleted memory with the Raster engine:
> >
> > const int w = 16, h = 16;
> > QRgb* data = new QRgb[w*h*4];
> > std::memset(data, 0, w*h*4);
> > QImage* i = new QImage(data, w, h, QImage::Format_ARGB32_Premultiplied);
> > QPixmap p = QPixmap::fromImage(*i);
> > delete i;
> > //Do stuff with p here
> >
> > There seems to be no deep copy going on here (and coincidentally,
> > QImage::convertToFormat docs lie --- it doesn't always return a copy)
>
> Yes it is possible, but I don't know where this copy happens at all.

Exactly, Maskim (and I) pointed out that there *is* no copy.
AFAICS, it would be enough to detach the QImage, alas detach() is internal.
How about

QImage* i = new QImage((const QRgb *)data, w, h, QImage::Format_ARGB32_Premultiplied);
(void)i.bits(); // detach from data

if the above is the actual code?

BTW: It probably works with OpenGL for you, because OpenGL is another
client/server system, i.e. the data is copied into an OpenGL-managed
area (possibly even the graphics card's memory).

HTH,
  Hans