How to use the "opengl" qt rendering backend instead of "raster"?

[René J.V. Bertin]

On Sunday May 20 2018 21:11:07 Clemens Eisserer wrote:
Hi,

>export QT_GRAPHICSSYSTEM=runtime
>export QT_DEFAULT_RUNTIME_SYSTEM=opengl
>export QT_GRAPHICSSYSTEM=opengl

Those are Qt4 controls, ones you could also set via the "Qt Graphics System" KCM for KDE4.
No wonder they have no effect if you use a KDE5/Plasma5 desktop nowadays. Do you? In that case, have you tinkered with the various options of the kwincompositing KCM?

AFAIK, Qt5 uses OpenGL for just about everything, but you could try to set QT_XCB_GL_INTEGRATION=xcb_egl (instead of xcb_glx) to see if that changes anything.

That KCM also lists the OpenGL backend as experimental, and I seem to recall that it certainly looked that way when I tried the option, once.

Either way, desktop effects like the transparent-moving-windows do use composing when available but also have a raster version. And at least in Plasma4, the preferred backend was "Raster" when using OpenGL, in order to avoid artefacts.

R.