Review Request 126205: If the user runs failsafe mode, use software rendering in QtQuick

[David Edmundson]

> On Nov. 30, 2015, 9:18 a.m., Martin Gräßlin wrote:
> > What does QT_XCB_FORCE_SOFTWARE_OPENGL?
> 
> David Edmundson wrote:
>     It makes Qt apps pretend LIBGL_ALWAYS_SOFTWARE is set.
> 
> Martin Gräßlin wrote:
>     Sorry, but that doesn't do what you hope it does:
>     
>     - only affects Mesa drivers
>     - if Mesa is broken for whatever reason the software rasterizer will also be broken
>     - kwin does something completely different with failsafe: no OpenGL at all.
>     
>     So if you get crashers due to e.g. broken NVIDIA driver, this won't fix it.
> 
> David Edmundson wrote:
>     Yeah, I knew it didn't fix nvidia. 
>     
>     I know it's not perfect, but I have seen user's on bugzilla with positive results from it, so when I saw this code block (whilst editing something else) it seemed like it might fix some situations, and I can't see any real downsides.
> 
> Martin Gräßlin wrote:
>     > I can't see any real downsides
>     
>     the downside is that it switches to CPU rendering. Which seems not the best thing to do in general. I cannot imagine a situation where the actual mesa drivers are broken and llvmpipe wouldn't be broken, too. So I just don't see what this would improve for fail safe. I don't see a possible improvment, so for me the downside (CPU rendering) seems worse. Any pointers to bug reports where users had a broken mesa, but a still working llvmpipe can change my mind ;-)

The Intel fiasco (so one bug a trillion billion times)
https://bugs.kde.org/show_bug.cgi?id=349519#c28

and openGL < 2 hardware
https://bugzilla.redhat.com/show_bug.cgi?id=1249280#c1

Fedora ended up with an xinit script that sets this env var in some cases (which is a bit weird given it's a condition I'm sure Qt could easily check itself) http://pkgs.fedoraproject.org/cgit/qt5-qtbase.git/tree/10-qt5-check-opengl2.sh


- David


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On Nov. 30, 2015, 9:13 a.m., David Edmundson wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://git.reviewboard.kde.org/r/126205/
> -----------------------------------------------------------
> 
> (Updated Nov. 30, 2015, 9:13 a.m.)
> 
> 
> Review request for Plasma.
> 
> 
> Repository: plasma-workspace
> 
> 
> Description
> -------
> 
> Graphics seem more likely than anything else to be broken, if the user
> explicitly selects failsafe mode from the DM we should follow the same
> rationale as kwin and not trust the user's drivers.
> 
> 
> Diffs
> -----
> 
>   startkde/startkde.cmake 41a8975cce1fb2a4e7a034e697ce6e2cc59d5b1e 
> 
> Diff: https://git.reviewboard.kde.org/r/126205/diff/
> 
> 
> Testing
> -------
> 
> 
> Thanks,
> 
> David Edmundson
> 
>

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