'Re: Review Request: frame plasmoid: image load and scaling with'

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List:       kde-panel-devel
Subject:    Re: Review Request: frame plasmoid: image load and scaling with
From:       "Davide Bettio" <davide.bettio () kdemail ! net>
Date:       2010-03-08 13:33:12
Message-ID: 20100308133312.12884.71376 () localhost
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> On 2010-03-08 11:47:49, Sebastian Kügler wrote:
> > I'm not sure about this patch:
> > 
> > - The loading of images in a thread is nice
> > - The "loads huge picture and keeps them in mem" is not changed (in \
> > fact, it's worse now since QImage forces you to keep them in system \
> >                 memory, whereas QPixmaps can be stored on the graphics \
> >                 card)
> > - It basically disables hardware acceleration of the image scaling, \
> > QImage vs. QPixmap 
> > With QPixmaps, we can blit into a smaller rect which is very fast, with \
> > QImage, we have to do the scaling in software and then convert it to a \
> > QPixmap to draw it. This happens on every resize, so it's a hot path \
> > and blocks direct user interaction. In my tests on different hardware \
> > (ATI, Intel, NVidia), the QPixmap based approach "felt" faster \
> > (smoother, more frames per second while resizing). The performance here \
> > depends on the painting backend used (image vs raster vs native) \
> > though, and thus per driver. 
> > Maybe we can only do the image loading in a thread (since that can \
> > potentially take quite long for large images), and keep a smaller copy \
> > (screen resolution?) stored in a QPixmap which is then used to resize. \
> > (If a size larger than our screen resolution is required, we can \
> > on-demand load the full image (40000x30000px if you wish ;)) and scale \
> > from that. (Rationale upscaling == bad, downscaling == OK, saving mem \
> > == good) 
> > The patch as it's now is not good enough IMO.

We must do software scaling because loading a 4000x3000 pixmap into X11 and \
asking X11 to scale the pixmap is a bad idea and it freezes the whole X11 \
environment including plasma and kwin for at least a couple of seconds \
(that happpens on a recent nvidia quadro, and I wonder what happens on an \
ATI video card powered with buggy drivers). With this patch during resize \
paintInterface is called and the cached QPixmap is used, in the meantime \
another thread with a completely async behaviour scales the image.

> The "loads huge picture and keeps them in mem" is not changed (in fact, \
> it's worse now since QImage forces you to keep them in system memory, \
> whereas QPixmaps can be stored on the graphics card)
Do you know how to load our image on graphics card memory without blocking \
everything? (don't forget that 4000x3000 px images are about 45 mb of raw \
ARGB data) And moreover what's the point of using video card memory since \
system memory is larger (think about laptops too) when moreover we don't \
need to use any video card feature? I can try anyway to reduce the huge in \
memory image footprint, but honestly I think that I should commit this \
patch before and then I can solve that problem. Anyway a solution might be \
to start after N seconds a thread with really low priority that replaces \
the huge in memory image with a screen-resolution-one (doing this task \
during image load and display process might be a bad idea).

> Maybe we can only do the image loading in a thread (since that can \
> potentially take quite long for large images).
This will prevent to freeze plasma during image loading but then X11 will \
be freezed anyway.

I might try to improve also the behaviour using a thread with a bit lower \
priority than the default priority.

Anyway don't forget that we are using software scaling also for wallpapers \
since KDE 4.0 and it works nicely.

- Davide

-----------------------------------------------------------
This is an automatically generated e-mail. To reply, visit:
http://reviewboard.kde.org/r/3162/#review4411
-----------------------------------------------------------

On 2010-03-08 02:27:47, Davide Bettio wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> http://reviewboard.kde.org/r/3162/
> -----------------------------------------------------------
> 
> (Updated 2010-03-08 02:27:47)
> 
> 
> Review request for Plasma.
> 
> 
> Summary
> -------
> 
> First of all: **This is a preview of the patch** I'm still working on it \
> but I need some advices. Picture Frame does 2 really bad things (when \
>                 used with huge images):
> * it loads huge images (in my case 4000x3000 pixels) into X11 pixmaps
> * plasma is blocked while the image is scaled
> As side effect also X11 freezes.
> 
> This patch solves both issues using threads.
> 
> I think that we should remove "smooth scaling" option from our \
> configuration UI. what do you think? 
> 
> Diffs
> -----
> 
> /trunk/KDE/kdeplasma-addons/applets/frame/CMakeLists.txt 1093624 
> /trunk/KDE/kdeplasma-addons/applets/frame/appearanceSettings.ui 1093624 
> /trunk/KDE/kdeplasma-addons/applets/frame/configdialog.h 1093624 
> /trunk/KDE/kdeplasma-addons/applets/frame/configdialog.cpp 1093624 
> /trunk/KDE/kdeplasma-addons/applets/frame/frame.h 1093624 
> /trunk/KDE/kdeplasma-addons/applets/frame/frame.cpp 1093624 
> /trunk/KDE/kdeplasma-addons/applets/frame/imageloader.cpp PRE-CREATION 
> /trunk/KDE/kdeplasma-addons/applets/frame/imagescaler.cpp PRE-CREATION 
> /trunk/KDE/kdeplasma-addons/applets/frame/picture.h 1093624 
> /trunk/KDE/kdeplasma-addons/applets/frame/picture.cpp 1093624 
> /trunk/KDE/kdeplasma-addons/applets/frame/slideshow.h 1093624 
> /trunk/KDE/kdeplasma-addons/applets/frame/slideshow.cpp 1093624 
> 
> Diff: http://reviewboard.kde.org/r/3162/diff
> 
> 
> Testing
> -------
> 
> 
> Thanks,
> 
> Davide
> 
> 

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