QGraphicsView based applications garbled rendering in kvm with cirrus video driver

[Florian Boucault]

Steps to reproduce:

1. Launch Oneiric in a kvm virtual machine
2. open up a terminal and launch "qmlviewer" part of the qt4-qmlviewer package

Screenshot of the current result:

http://ubuntuone.com/p/wsM

[Florian Boucault (fboucault)]

qtdemo exhibits similar artifacts: http://ubuntuone.com/p/wsD

[Florian Boucault (fboucault)]

@Jonhatan: can you please not mark this bug as duplicate of https://bugs.launchpad.net/ubuntu/+source/unity-2d/+bug/759803

#759803 describes 2 separate issues in Unity 2D. Both these issues were determined to be in fact issues with Qt and kvm (cirrus) and were reported seperately against qt4-x11 with ways to reproduce independent from Unity 2D:

https://bugs.launchpad.net/ubuntu/+source/qt4-x11/+bug/791140
https://bugs.launchpad.net/ubuntu/+source/qt4-x11/+bug/791133

[Jonathan Thomas (echidnaman)]

It's pretty clear that the cirrus driver is the root cause of all these issues.

[Marc Pignat (swid)]

Hi all!

I have seen that in when network booting a virtual machine...

The bug was fixed in syslinux 3.54, and the changlog says :
"vesamenu: fix handing of VESA modes with noncontiguous memory buffers. In particular, Qemu/KVM sets up such a mode when Cirrus Logic emulation is enabled (which is the default.)"

I think qt4-x11 has the same problem!

[Marc Pignat (swid)]

This bug belongs to mesa, this is a software rendering bug

[Marc Pignat (swid)]

And a good new:
I have sent a patch upstream, and it has been accepted:

fix commit : c0c0bb6cb140825f5bab3c40c0c9c0ec575fbc76 (tree git://anongit.freedesktop.org/mesa/mesa)

Best regards

Marc

[Marc Pignat (swid)]

It seems that I broke 32 bpp in this commit, but I'm working on it!

[Marc Pignat (swid)]

New patch posted upstream and waiting for approval.

[Florian Boucault (fboucault)]

@Marc: I am sorry but I do not understand what this bug has to do with mesa. I don't think OpenGL is used at any point in the rendering. qmlviewer by default will use the "native" backend which on Linux is XRender.

[Marc Pignat (swid)]

@Florian: It seems you're right...

qtdemo uses opengl as graphicssystem
qmlviewer uses raster as graphicssystem

So those 2 bugs are separated.

My patch fixes the opengl rendering issue

[Marc Pignat (swid)]

Some more info about qmlviewer:

qmlviewer -graphicssystem native -> works
qmlviewer -graphicssystem opengl -> does not work
qmlviewer -graphicssystem raster -> does not work

it seems that qmlviewer without args uses the raster graphic system... like unity-2d

qmlviewer -graphicssystem opengl work with mesa patched ;)

[Marc Pignat (swid)]

qmlviewer does not uses mesa, this bug is triggered using the raster paint engine