xscreensaver - two displays and fliptext bottom pixel line on one display draws on wrong display

[Chris Guiver]

Lubuntu 20.04 QA-testing play on hp dc7700 (c2d-e6320, 5gb, nvidia quadro nvs 290)

1. Boot Lubuntu 20.04 daily ISO on box
2. I adjust displays (LXQt.Monitor.Settings) to match my setup (one above the other)
   In theory LXQt.Monitor.Settings will not allow for overlap (still possible in Lubuntu); I had displays NOT touch each other (ie. gap between) letting the 'apply' snap the displays so they were correctly touching
3. Change default (flurry) to (flipflop)
4. Click PREVIEW to display

Expected Result:

Images on each display not related to each other

Actual Result:

When the top display image touches the bottom of my 'upper' display, the color appears on my 'lower' display. The actual image on my 'lower' display is well away from top of screen. As the top image 'flips' and color squares no longer go 'off' screen; they also disappear from my bottom display.

The effect is NOT unpleasant; it looks like reflection from the bottom (as colors (red, yellow, blue) are the same on both displays - but it's unintended.

I've noted this behavior before & it was filed upstream to LXQt; they eventually blamed openbox.

I've installed `sudo apt install xfwm4` then `xfwm4 --replace` to attempt to replace openbox with wfwm4 (whilst running 'live') and the issue remained still.

I also swapped my displays (so my-top was at the bottom, and my-bottom was on-top) and xscreensaver now only hid one display - however I did get the top line of pixels on the display which was no longer covered by xscreensaver. This behavior has been noted before many times, but was linked to the xscreensaver only covering single display (http://launchpad.net/bugs/1814490)

I have now separated the issue (top pixel line on wrong display) - however it's still possible they are linked. If displays are left-right placed; the pixel line appears still on the wrong display, but at side of display. This issue is not new (being noted on other bug reports as secondary noticed issue until today).

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: xscreensaver 5.42+dfsg1-1ubuntu1
ProcVersionSignature: Ubuntu 5.3.0-24.26-generic 5.3.10
Uname: Linux 5.3.0-24-generic x86_64
ApportVersion: 2.20.11-0ubuntu13
Architecture: amd64
CasperVersion: 1.434
CurrentDesktop: LXQt
Date: Sat Dec 7 04:56:51 2019
LiveMediaBuild: Lubuntu 20.04 LTS "Focal Fossa" - Alpha amd64 (20191206)
SourcePackage: xscreensaver
UpgradeStatus: No upgrade log present (probably fresh install)

[Chris Guiver (guiverc)]

(the issue is not new comment is because I believe I first noticed it on 17.10 pre-release)

[Ubuntu QA Website (ubuntuqa)]

This bug has been reported on the Ubuntu ISO testing tracker.

A list of all reports related to this bug can be found here:
http://iso.qa.ubuntu.com/qatracker/reports/bugs/1855517

[Chris Guiver (guiverc)]

Lubuntu 20.04 qa-test play on dell [optiplex] 780 (c2q-q9400, 8gb, amd/ati cedar radeon hd 5000/6000/7350/8350)

I could re-create it here, but also noted `vlc` was also causing the same reaction in certain display configurations. As before to ensure I don't have 'overlap' I position the screens to there is a space between them, then let the Monitor.Settings bring them together... I suspect the flaw is here (ie. it's causing a 1+ pixel overlap??

I'll change package from xscreensaver to lxqt-config

[ԜаӀtеr Ⅼарсһуnѕkі (wxl)]

Is this still an issue in Jammy, Mantic or Noble?