[Interest] allocate QImage data in QSharedMemory

[Philip Schuchardt]

Josh, I'm curious how this worked out for you? Were you able to get the CPU
load down?


On Mon, Dec 12, 2016 at 5:03 PM Joshua Grauman <jnfo-c at grauman.com> wrote:

> Brilliant! How did I miss that constructor?!
>
> Josh
>
> > Hi,Why not construct the image object from the shared memory buffer to
> begin with? Then lock the sm while drawing.
> > Look for example this constructor:
> http://doc.qt.io/qt-5/qimage.html#QImage-3
> >
> > On Mon, Dec 12, 2016 at 11:45 PM, Joshua Grauman <jnfo-c at grauman.com>
> wrote:
> >       Hello all,
> >
> >       I have been able to generate a screen capture of my program by
> rendering a window into a QImage at 30fps (called from QTimer), and then
> copying the QImage to shared memory
> >       (QSharedMemory) where another program grabs the frames and outputs
> them to ffmpeg. It all works great.
> >
> >       However, my cpu is barely keeping up if I do much on my app.
> >
> >       One of the ways I thought of to speed it up is to avoid the memcpy
> from the QImage (img) to QSharedMemory (sharedMemory) by deriving from
> QImage to a new class
> >       (QSharedMemoryImage) which allocates its image data in shared
> memory to begin with so that the window->render() function renders the
> window right into shared memory so the copy
> >       isn't necessary. QImage was a bit too complex for me to figure out
> how to do this.
> >
> >       For you experts, is this possible? How hard would it be?
> >
> >       Here's the relevant code in the QTimer:
> >
> >         window->render(&img, QPoint(), QRegion(), QWidget::DrawChildren);
> >         sharedMemory.lock();
> >         char *to = (char*)sharedMemory.data();
> >         const unsigned char *from = img.constBits();
> >         memcpy(to, from, sharedMemory.size());
> >         sharedMemory.unlock();
> >
> >       Josh
> >       _______________________________________________
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> >       http://lists.qt-project.org/mailman/listinfo/interest
> >
> >
> >
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-- 
Phi|ip
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