'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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