[Development] [QML] Avoiding graphics flicker in Quick2

Denis Shienkov denis.shienkov at gmail.com
Fri Aug 5 11:02:10 CEST 2016


> Can you try a plain OpenGL test application with RGBA8 framebuffer

Do you mean: I should take any OpenGL application from the Qt examples? And
to check there?

2016-08-05 11:53 GMT+03:00 Sean Harmer <sean.harmer at kdab.com>:

> Hi,
>
> Can you try a plain OpenGL test application with RGBA8 framebuffer and see
> if
> that exhibits the same flashing/flickering problem. If so, it's a
> driver/hardware issue.
>
> If you are forced into then using a 16-bit framebuffer, then you can avoid
> the
> banding by using dithering in your gradients. Either apply the dithering
> offline
> and store the gradients as images or write a custom material that applies
> the
> dithering in the fragment shader.
>
> Cheers,
>
> Sean
>
> On Friday 05 August 2016 08:12:59 Denis Shienkov wrote:
> > Hi all,
> >
> > I have an idea how to avoid flickering, but I don't know about results:
> > what if I will discard the Open GL support in favor to Quick2 render?
> >
> > I have read this documentation: http://doc.qt.io/QtQuick2DRenderer/
> > which says about the "Qt Quick 2D Renderer" module.
> >
> > So, my things is:
> >
> > 1. Download && build && install  this module:
> >
> > git://code.qt.io/qt/qtdeclarative-render2d.git
> >
> > 2. Use this env variable:
> >
> > export QMLSCENE_DEVICE=softwarecontext
> >
> > 3. Run my app...
> >
> >
> > But, I  don't understand:
> >
> > 1) What of engine is used to 2D rendering in case if I have EGLFS only?
> >
> > 2) Should I re-build Qt5 too with the "--no-opengl" option (or I can
> > keep the "-opengl es2" option) ?
> >
> > 04.08.2016 16:10, Denis Shienkov пишет:
> > > Hi Robin,
> > >
> > > > Repeating my last answer...
> > > > http://lists.qt-project.org/pipermail/development/2016-
> July/026736.html
> > >
> > > I'm sorry, but I did not receive (did not see) your last answer.
> > >
> > > > I'm going to guess you're using eglfs or something like that
> > >
> > > Yes, I use EGLFS via X11 on Linux Apalis T30 board, where are used
> > > NVIDIA's drivers.
> > >
> > > Seems, the flickering is when are used:
> > >
> > > export QT_QPA_EGLFS_FORCE888=1
> > >
> > > ENV variable... (I need this variable to smooth the Image's
> > > gradients... even X11 started with 24-bit depth).
> > >
> > > PS: But, I'm not sure about QT_QPA_EGLFS_FORCE888... :(
> > >
> > > > Using an overlay to debug item positions (QSG_VISUALIZE=overdraw)
> > >
> > > could be handy for trying to rule
> > > this out, as if it is specific to the application,
> > >
> > > Ok, many thanks, I will try it.
> > >
> > >
> > > 2016-08-04 14:57 GMT+03:00 Robin Burchell <robin+qt at viroteck.net
> > >
> > > <mailto:robin+qt at viroteck.net>>:
> > >     Repeating my last answer...
> > >
> > >     http://lists.qt-project.org/pipermail/development/2016-
> July/026736.htm
> > >     l
> > >
> > >     On Thu, Aug 4, 2016, at 01:50 PM, Denis Shienkov wrote:
> > >     > {quote}
> > >     >
> > >     > Hi all.
> > >     >
> > >     > I have some QML application, where just use QQuickView as QML
> > >
> > >     container.
> > >
> > >     > This application uses Qt 5.7.x and running on Linux embedded
> > >
> > >     board with
> > >
> > >     > the
> > >     > NVIDIA core (Toradex Apalis T30).
> > >     >
> > >     > But sometimes I got flickering in process of animation. A
> flickering
> > >     > represents in form of a "white" strips with full-screen width
> > >
> > >     and 1/5-1/6
> > >
> > >     > screen heigth. This flickers happens quickly and frequently
> > >
> > >     (every ~20-60
> > >
> > >     > seconds, randomly)...
> > >     >
> > >     > I have seen this "Avoiding graphics flicker in Qt / QML" [1]
> > >
> > >     blog where
> > >
> > >     > are
> > >     > used QML with Qt 4.x,
> > >     > where were used this trics:
> > >     >
> > >     > {code}
> > >     > int main(int argc, char **argv)
> > >     > {
> > >     >
> > >     >     ...
> > >     >
> > >     >  view.setAttribute(Qt::WA_OpaquePaintEvent);
> > >     >  view.setAttribute(Qt::WA_NoSystemBackground);
> > >     >  view.viewport()->setAttribute(Qt::WA_OpaquePaintEvent);
> > >     >  view.viewport()->setAttribute(Qt::WA_NoSystemBackground);
> > >     >
> > >     >     ...
> > >     >
> > >     > }
> > >     > {code}
> > >     >
> > >     > But, in my case I have use Quick v2, with QQuickView instead of
> > >     > QDeclarativeView,
> > >     > which does not allowed to setup any attributes.
> > >     >
> > >     > So, my questions is: is there are any way to setup
> > >     > Qt::WA_OpaquePaintEvent
> > >     > and/or
> > >     > Qt::WA_NoSystemBackground in Quck2? Or, maybe is it possible to
> use
> > >     > another
> > >     > tricks?
> > >     >
> > >     > BR,
> > >     > Denis
> > >
> > >     [1]https://blog.rburchell.com/2011/11/avoiding-graphics-
> flicker-in-qt-> >     qml.html>
> > >     > {quote}
> > >     >
> > >     > This flickering present on some HDMI displays...
> > >     >
> > >     > We currently have this flags:
> > >     >
> > >     > {code}
> > >     > ...
> > >     > view.setFlags(Qt::FramelessWindowHint |
> Qt::WindowStaysOnTopHint);
> > >     > ...
> > >     > {code}
> > >     >
> > >     > Maybe is it an reasons of flikering? Has someone any ideas?
> > >     >
> > >     > BR,
> > >     > Denis
> > >     > _______________________________________________
> > >     > Development mailing list
> > >     > Development at qt-project.org <mailto:Development at qt-project.org>
> > >     > http://lists.qt-project.org/mailman/listinfo/development
>
> --
> Dr Sean Harmer | sean.harmer at kdab.com | Managing Director UK
> KDAB (UK) Ltd, a KDAB Group company
> Tel. +44 (0)1625 809908; Sweden (HQ) +46-563-540090
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