[r100] rendering artifacts: intermittent vertical lines on right side of round shapes

[Karl Ostmo]

Binary package hint: xserver-xorg-video-ati

The artifacts are single-pixel-wide vertical lines on the right edge of what is probably the shape's bounding box. They appear in the same color as the source color of the shape. I originally reported this as a bug in Cairo (see https://bugs.freedesktop.org/show_bug.cgi?id=13871), but it was suggested that this was actually a bug in the x server. I have attached a screenshot of the phenomenon occurring on OpenOffice Draw, also (which does not currently use Cairo).

I have noticed that it is possible to "wipe" the artifacts away by dragging another window across the offending regions, but the same action can also cause the artifacts to reappear.

I am running Ubuntu Gutsy with Desktop Effects (Compiz) disabled.

kostmo@lapster:~$ lspci | grep VGA
01:00.0 VGA compatible controller: ATI Technologies Inc Radeon Mobility M7 LW [Radeon Mobility 7500]

[Karl Ostmo (kostmo)]

Created an attachment (id=13428)
Python program to demonstrate artifacts

You can type "pydoc cairo_artifact_testcase" for some more info.

[Karl Ostmo (kostmo)]

Created an attachment (id=13429)
Image that demonstates the artifact

Look at the right edge of the circle. There is a thin vertical line of red pixels.

[Carl Worth (cworth)]

I've seen this kind of thing before, and I believe it is a bug in the X server, not cairo. What X server and driver are you running and what versions? Is it an ATI card by chance?

-Carl

[Karl Ostmo (kostmo)]

My card is an ATI Radeon Mobility 7500. I'm running Ubuntu Gutsy, so I think the driver being used is the free "ATI" driver. Not sure how to determine the version of the xserver. Come to think of it, though, I have seen similar vertical line artifacts on the "r" character for quite some time on Ubuntu in non-Cairo environments, so you may be right in that it is not a Cairo bug.

[Karl Ostmo (kostmo)]

Binary package hint: xserver-xorg-video-ati

The artifacts are single-pixel-wide vertical lines on the right edge of what is probably the shape's bounding box. They appear in the same color as the source color of the shape. I originally reported this as a bug in Cairo (see https://bugs.freedesktop.org/show_bug.cgi?id=13871), but it was suggested that this was actually a bug in the x server. I have attached a screenshot of the phenomenon occurring on OpenOffice Draw, also (which does not currently use Cairo).

I have noticed that it is possible to "wipe" the artifacts away by dragging another window across the offending regions, but the same action can also cause the artifacts to reappear.

I am running Ubuntu Gutsy with Desktop Effects (Compiz) disabled.

kostmo@lapster:~$ lspci | grep VGA
01:00.0 VGA compatible controller: ATI Technologies Inc Radeon Mobility M7 LW [Radeon Mobility 7500]

[Karl Ostmo (kostmo)]

Please look at the upper-right tip of some of these "r" characters to see the artifact.

[Karl Ostmo (kostmo)]

Look at the right edge of the circle. There is a thin vertical line of red pixels. This is an application I wrote using PyCairo specifically to demonstrate this artifact. This is a single "arc" primitive in Cairo, and the artifact line does not extend from top to bottom of the circle, so I guess it might not be related to the "bounding box" of the shape after all.

[Bugzi09-fdo-tormod (bugzi09-fdo-tormod)]

(Why was the bug closed instead of reassigned?)

[agd5f (agd5f)]

Please attach xorg log and config. Do you still get drawing problems with the vesa driver or with "NoAccel?" How about XAA vs. EXA?

[Karl Ostmo (kostmo)]

Created an attachment (id=13549)
xorg.conf before modifying anything

[Karl Ostmo (kostmo)]

Created an attachment (id=13550)
Xorg.0.log before modifying anythin

[Karl Ostmo (kostmo)]

(In reply to comment #6)
> Please attach xorg log and config. Do you still get drawing problems with the
> vesa driver or with "NoAccel?" How about XAA vs. EXA?
>

I changed the driver from ATI to Vesa, then restarted the computer. I am unable to reproduce the bug when using the Vesa driver.

[Tormod Volden (tormodvolden)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. Please attach your X server configuration file (/etc/X11/xorg.conf) and X server log file (/var/log/Xorg.0.log) to the bug report as individual uncompressed file attachments using the "Attachment:" box below. Could you please also try to run without any /etc/X11/xorg.conf and let Xorg autodetect your display and video card? Please also attach the /var/log/Xorg.0.log from this attempt. Thanks in advance.

[agd5f (agd5f)]

Can you try EXA vs XAA?
Option "AccelMethod" "XAA" # the default
or
Option "AccelMethod" "EXA"

Next, can you try and find out what operation is causing the problem? For XAA try the following options:

Option "XaaNoOffscreenPixmaps"
Option "XaaNoSolidFillRect"
Option "XaaNoScreenToScreenCopy"
etc. (see xorg.conf man page).

EXA has similar options (see exa man page).

[Karl Ostmo (kostmo)]

(In reply to comment #10)

{Option "AccelMethod" "EXA"} made the artifacts disappear, however rendering was noticeably slower (and "Desktop Effects" could not be enabled; when attempting to do so the xserver kicked me out to the login screen).

I tried the 3 options you gave one at a time under XAA. Setting either {Option "XaaNoOffscreenPixmaps"} or {Option "XaaNoScreenToScreenCopy"} alone eliminated the artifacts, while still preserving accelerated rendering (including "Desktop Effects"). {Option "XaaNoSolidFillRect"} did not help anything.

[Michel-tungstengraphics (michel-tungstengraphics)]

If Option "RenderAccel" "off" works around it as well, it could be the infamous bug 1424. Can you try xf86-video-ati 6.7.197 or Git?

[Bugzi09-fdo-tormod (bugzi09-fdo-tormod)]

Karl, you can get updated-from-git test packages for Ubuntu Gutsy at https://wiki.ubuntu.com/XorgOnTheEdge

[Brian Murray (brian-murray)]

Thanks for taking the time to report this bug and helping to make Ubuntu better. In the development cycle for Intrepid there have been some vast improvements in the open source ati video driver and we could use your help testing them. Could you please download the latest Alpha CD image of Intrepid and test this particular bug just using the Live CD? You can find the latest image at http://www.ubuntu.com/testing . Your testing can help make Ubuntu and the open source ati driver even better! Thanks in advance.

[Karl Ostmo (kostmo)]

I downloaded and installed Intrepid Alpha 4. I spent several minutes with my Python testcase trying to get the artifacts to appear, but the bug appears to be fixed! Good job!

I was not able to enable Desktop Effects with the Intrepid fresh installation, but I suppose that's a different problem. `glxinfo` says that Direct Rendering is enabled, but I'm not sure how to tell what display driver is in use; xorg.conf looks a lot shorter than it used to be, the "ati" string is nowhere to be found.

[Bryce Harrington (bryce)]

We are no longer seeing this issue (ref LP #180654); I believe it can be closed as resolved.

[Brian Murray (brian-murray)]

You could use 'lsmod' to determine which video driver is being used. For example:

lsmod | grep radeon

radeon 153248 2
drm 108128 3 radeon

[Bryce Harrington (bryce)]

Thanks for letting us know the issue no longer occurs with the newer X code. Of course, feel free to reopen with further details if the problem crops up again.