#27 long lines suddenly appear

[Anonymous]

A few times a session, while drawing, a long line running the entire length of the page will appear, starting from the current position of the pen, and ending off the page. I am running Xournal on a thinkpad tablet, which uses the wacom linux drivers for the pen.

Sometimes, a very short and very thick line will appear.

[Denis Auroux]

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Thanks for the report. However I can't say definitely what's going on without more details.

- for the long lines, one possibility is that your system generates an invalid event with incorrect coordinates (pretending that your pen "teleported" to a completely different place on the screen). Do you have the multitouch screen, and if so is the multitouch feature enabled? (in that case, could it be that the touch-screen device sporadically reports that you've clicked in a corner of the screen?) Similarly if you have other devices that could interfere with the tablet input data.

- for the short thick lines, this may be a display bug -- there's definitely a few bugs in libgnomecanvas which occasionally cause extra horizontal lines to appear in xournal, but these normally go away when refreshing the display (e.g. zooming in or out). Is that the case for yours?

If you save the .xoj file and reload it, do any of the extra lines you report (either the long ones or the short thick ones) appear, or are they gone? If they're gone it's probably just a display bug, most likely in the libgnomecanvas or libart libraries; if not, please post here or e-mail me a .xoj file that contains such lines (without erasing, moving, or otherwise editing the strokes that contain these lines). This may give a clue to what happened.

Also let me know what distribution (what version) you are using.

Thanks,
Denis

[Nobody/Anonymous]

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I have something similiar.
I copied a small part out of a bigger .xoj file that produces a horizontal line at certain zoom-levels.
If you zoom in a couple of times you should be able to see a horizontal line right to the center.

http://www.fast-load.net/index.php?pid=f32a72d78e44dbb46e7a606610b2f2fd

[Denis Auroux]

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The link you provided doesn't work. Can you just upload the file here (there's an "upload file" button at the bottom of this page), or e-mail it to me (my login @ math.mit.edu) ?
Thanks,
Denis

[Denis Auroux]

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Thanks a lot for sending me the file. Yes, I see what you mean. It's similar to something I have observed sometimes myself, and I believe it is a bug in libgnomecanvas (the library that xournal uses to handle the on-screen display). (One way to tell is that it only occurs at very specific zoom levels...).

It would be good to get this bug fixed, but I think it is a very complicated interaction between xournal, libgnomecanvas, and the libart library that libgnomecanvas in turn uses to actually draw things - so it will probably be difficult to figure out what causes it.

The original bug report mentions two types of unwanted lines. Do they both disappear when
zooming in/out (if so it's the same problem in both cases), or do some of them stay? If the latter, I'd be interested in more details and maybe a file containing such a line.

Thanks,
Denis

[Michael Wayne Goodman]

I noticed this as well on my x61t. It is not just Xournal, but other programs (Gimp), and I may have even seen it in the normal filesystem UI (dragging a file, for example). I have the multitouch screen, but that feature was turned off (eg. no entry for it in xorg.conf). It seemed that the line would jump to certain places on the screen (very left side, either the middle or bottom, sometimes to the top side in the center) where I imagine there are either pressure points (triggering the multitouch) or some sort of sensor for the stylus, but this is just a guess.

Somewhat worryingly, the behavior suddenly stopped happening for no apparent reason. I no longer experience it, but I have no idea if it will come back again. I was using Ubuntu 8.04 at the time.

I had a pdf showing the behavior, but I cannot find it now. Sorry.

Either way, it does not appear to be a Xournal bug. It is likely related to the hardware (since the reporter said he/she had a thinkpad as well). Unless there is evidence of something else going on, I'd suggest closing the bug.