VLC interface not displayed correctly on external display

[FalCT60]

I use vlc on a Dell E-5530 laptop seated on its docking station.
The laptop display cover is closed, the output is sent on an external LG TV with 1920x1080.
This system has been working flawlessly for many years, resp. under late 14.04 and 16.04.
After recently upgrading to 18.04, I noticed VLC wouldn't display correctly - see attachment.
This only occurs on the external display ; if I open the cover and use the internal display, there is no problem - except I cannot work on the internal display.
regards,
J.-Luc

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: vlc-bin 3.0.4-1ubuntu0.2
ProcVersionSignature: Ubuntu 4.15.0-43.46-generic 4.15.18
Uname: Linux 4.15.0-43-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.5
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Wed Jan 2 23:38:36 2019
ExecutablePath: /usr/bin/vlc
InstallationDate: Installed on 2018-12-19 (14 days ago)
InstallationMedia: Ubuntu 18.04.1 LTS "Bionic Beaver" - Release amd64 (20180725)
ProcEnviron:
 PATH=(custom, user)
 XDG_RUNTIME_DIR=<set>
 LANG=fr_FR.UTF-8
 SHELL=/bin/bash
SourcePackage: vlc
UpgradeStatus: No upgrade log present (probably fresh install)

[FalCT60 (jean-luc-ceccoli)]

2 more hardcopies.

[Sebastian Ramacher (s-ramacher)]

This looks like the typical Qt HiDPI breakage and needs to be fixed in Qt. As a temporary workaround, disable scaling for Qt.

[roussel geoffrey (roussel-geoffrey)]

Hi, I think it's the same bug, i got a laptop with a second screen plugged, optimus laptop, nvidia-drivers-390, on the integrated laptop screen, vlc works just fine, but as soon as i drag the vlc window to the second screen GUI elements gets extra zoomed, and unusable ( but i can see some parts of GUI buttons reacting to mouse-over events for exemple). If i drag n drop a video file to the vlc window while on second screen the vlc window gets extra large and still displays extra zoomed GUI elements. note that if i drag the window back the laptop screen it's back to normal.

I tried to use QT_AUTO_SCREEN_SCALE_FACTOR=1 and QT_SCALE_FACTOR=1.5 but no change.

"cvlc" can play the videos normally on second screen (started from a terminal).

(stock Ubuntu 18.04)
(note on the screenshots: it's running fluxbox window manager, first screen ends at the right of the bottom bar and system infos displays - then on the right the second screen)

[roussel geoffrey (roussel-geoffrey)]

Another screenshot playing a video...

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Dmitry Shachnev (mitya57)]

Can one of you please check if the issue still exists with Ubuntu 19.04 (which has Qt 5.12)?

[roussel geoffrey (roussel-geoffrey)]

I just checked and the bug is still there on 19.04.

[roussel geoffrey (roussel-geoffrey)]

I also tested 18.04 again with another setup, still dual screen on a samsung TV, the vlc GUI is exageratly zoomed but still correctly visible and usable, not sure if they want it to be zoomed like that.

[roussel geoffrey (roussel-geoffrey)]

On my last test (the one where it works but is exageratly zoomed), when switching to fullscreen mode, the VLC overlays(control buttons, volume, etc) are not usable because too large, they don't fit on screen.

[FalCT60 (jean-luc-ceccoli)]

This is the behaviour I have been describing from the beginning : the video is useable, but most of the controls are not.
This happens on *every* laptop used with an external TV as main screen since 18.04 - it was fine until 16.04.
I would event bet it alson happens on every computer using a second monitor as main display unit.
In order to be able to use vlc correctly, I have to launch it from terminal with the command QT_AUTO_SCREEN_SCALE_FACTOR=0 vlc, which I could find in many of the thousands posts about this on the net since 2010 or so.
Which tends to prove that the bug has never been reported, otherwise no doubt the devs would have fixed it already.
And would not have thought that I was the only one to encounter it.
To the devs : I am ready to help you trying to trace this, but keep in mind that, just like you, I have a real life beside, which makes I may not react as quickly as one would expect.
This is also why I did not give any reminder though there was no reaction after a long time : I know you have many things to do, that may be more important (or valualble), and 24 hours per day are not enough for many of us.
This bug kind of puzzles me, and I sometimes wonder if I did not install something the wrong way : many things changed since 16.04, so being able to tell what is good or not is not that easy for a poor end user.
If I find some time, I plan to load the latest 16.04 LTS iso and reinstall it from scratch, but without preserving my /home. This means I will have to do some savings before, and be very carefull, and it will take me far more time then just upgrading my distro.
However, I may take some time to do some testings, a

[FalCT60 (jean-luc-ceccoli)]

Oops ! I hit the return key unintentionally !
So, I make take some time to do some testings, but you have to tell me what to do exactly, and how.

Regards,

J.-Luc

[roussel geoffrey (roussel-geoffrey)]

Hey, Thanks Jean Luc, the QT_AUTO_SCREEN_SCALE_FACTOR=0 does the trick here too!
I wonder if this only affects Ubuntu or other Linux distributions too.

[roussel geoffrey (roussel-geoffrey)]

As a temporary fix, so you don't have to launch it from the terminal you can do something like this, (need root):

sudo su
mv /usr/bin/vlc /usr/bin/vlcbin
echo 'QT_AUTO_SCREEN_SCALE_FACTOR=0 /usr/bin/vlcbin "$@"' > /usr/bin/vlc
chmod +x /usr/bin/vlc

It fixes the problem for me and i can launch it normally using the icon or from the file manager, i tested it with Nautilus and Nemo.