QT widget based UI rendering slow on qt5 when ported from qt4
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Hi.
I have similar issue with iMX6 && Qt5 && QtWidgets app. In my case I have created a simple test app, with an one widget which fills own rect 1280x800 every 50 msec with two colors 'red' and 'green'. In result I got the CPU loading ~50% on iMX6 against 0% on Desktop. But when I try to use the Qwt library, this loading increases to 100% on iMX6 against of 5% on a Desktop. I tried as 'linuxfb' and as 'eglfs' backends - result same.
I was sadly surprised in this, because, seems that Qt5 use the software QtWidgets rendering in any cases. So, now, I don't know what to do with this situation.
So, seems, you need to re-write your app to QtQuick... Or try to re-build your RootFS to use X11 with 'xcb' backend.
PS: It's easier for you to do this, because you do not use a real-time plotting.
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@kuzulis For porting an app from QtWidget to QtQuick will attract lot of development and testing time I believe so! My hardware does not support X11. I have heard we can build X11 free xcb is it?
The thing is everything works fine with QT4 (no X11 only Linux FB) but only with same image & hardware rendering is slow with QT5? I dont know the reason.
Is it because the way QT draws to buffer has changed? any solution or idea?
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I am not an expert. So, IMHO, just continue stays on Qt4. Qt5 does not given any advantages then for QtWidgets.
UPD:
I have found documentation mention about 'linuxfb' && 'eglfs' backends here. Where says that for QtWidgets used the software rendering.
Also I have found mention about X11 && 'xcb' backend here. Where it is unclear what of render is used for QtWidgets (I hope that sometihng hardware/accelerated 2D).
And I have not found any mention about 'directfb' backend on Qt5 && Linux.
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Widgets are using the rasteriser backend, so if you are thinking GPU, no they are not hardware accelerated.
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Please watch for current discussion in mailing-list.
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@kuzulis I have read the mailing list chain. I am interested in learning what is it that was in QT4 which is not in QT5 anymore from rendering perspective. With QT4 I used to run my app with -qws. ofcourse QT5 does not have qws. Is there anyway we can patch QT5 to enable similar features which were provided with qws in QT4.
If there is no workaround options with me would be either to migrate the app to qtquick which is huge effort or rollback to QT4. Is there any other option?
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Please read that mailing chain up to end (to today). There says that to the Qt5 are added one feature to enable the acceleration with QtWidgets && X11, using the QT_XCB_NATIVE_PAINTING env. variable. You can try it.
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@linuxsnail said in QT widget based UI rendering slow on qt5 when ported from qt4:
Does this mean that Qwidget can be accelerated as well?
Seems no.
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IIRC, DirectFB provided some hardware acceleration depending on the graphic chip you have at your disposal but don't expect NVIDIA Titan X acceleration performances.
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@SGaist I am still struggling with this topic, is there any possibility of adding software acceleration for qwidgets ? I'm just wondering what made it render faster on qt 4.8.1? even when we use qt4.8.7 it seems slow like qt5.
For qt4.8.1 and 4.8.7 my compile configurations are similar.
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If you are seeing a slowdown between Qt 4.8.1 and Qt 4.8.7, you should compare the code of both backend to see what's going on.
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What software acceleration do you have in mind ?
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You can use mesa for software based OpenGL rendering (don't expect hight performance).
SVG is not a screen rendering backend.
IIRC DirectFB should be faster than plain LinuxFB.
