The artifacts are single-pixel-wide vertical lines on the right edge of the shape bounding box. They appear in the same color as the source color of the shape. I have included a test case written with PyCairo to demonstrate this effect. To see the artifacts, resize the window. While you are dragging the window corner around, the artifacts will appear intermittently. The artifact is not present when the image is saved as a PNG at the same pixel dimensions. The artifact often disappears after another window is moved on top of the cairo surface and dragged off again, which forces a redraw of that part of the surface.
Created attachment 13428 [details] Python program to demonstrate artifacts You can type "pydoc cairo_artifact_testcase" for some more info.
Created attachment 13429 [details] Image that demonstates the artifact Look at the right edge of the circle. There is a thin vertical line of red pixels.
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
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.
(Why was the bug closed instead of reassigned?)
Please attach xorg log and config. Do you still get drawing problems with the vesa driver or with "NoAccel?" How about XAA vs. EXA?
Created attachment 13549 [details] xorg.conf before modifying anything
Created attachment 13550 [details] Xorg.0.log before modifying anythin
(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.
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).
(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.
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?
Karl, you can get updated-from-git test packages for Ubuntu Gutsy at https://wiki.ubuntu.com/XorgOnTheEdge
We are no longer seeing this issue (ref LP #180654); I believe it can be closed as resolved.
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