Background color erase (bce) is broken

[Boris Gjenero]

I'm running my ncursesw application, displaying a black background. When the screen or a region scrolls up by one line, empty areas of the screen in the newly visible line show the default white background of gnome-terminal.

If I remove the bce capability from the Terminfo for that terminal type, the problem goes away. This workaround involves:
"infocmp xterm-256color > xt.ti" to get the Terminfo data in text format.
Editing xt.ti and removing "bce, " on the 3rd line
"tic xt.ti" to compile this text to Terminfo again. Without sudo that ends up in ~/.terminfo, overriding the system's entry, and with sudo it would overwrite the system's Terminfo entry for that terminal type.

Another workaround would be to use a different terminal type without bce, like TERM=screen, but removing bce is better because that leaves other capabilities intact.

ProblemType: Bug
DistroRelease: Ubuntu 16.10
Package: gnome-terminal 3.20.2-1ubuntu5
ProcVersionSignature: Ubuntu 4.8.0-45.48-generic 4.8.17
Uname: Linux 4.8.0-45-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia
ApportVersion: 2.20.3-0ubuntu8.2
Architecture: amd64
CurrentDesktop: XFCE
Date: Fri Mar 31 13:49:01 2017
SourcePackage: gnome-terminal
UpgradeStatus: Upgraded to yakkety on 2016-10-13 (169 days ago)

[Egmont Koblinger (egmont-gmail)]

This was broken intentionally in order to fix another bug which is not fixable and not even workaroundable otherwise. See https://bugzilla.gnome.org/show_bug.cgi?id=754596. Although, as discussed there, we are aware of problems that we introduced and we have a few ideas how to improve (that is, partially revert) the behavior.

In order to help move forward, could you please share your app (or better, a tiny proof of concept, just the necessary steps extracted that demo the problematic behavior)?

[Egmont Koblinger (egmont-gmail)]

Boris,

I've added a patch to the linked VTE bug. Could you please let me know if it fixes your problem?

The simplest way of testing: download VTE, patch and compile it, and run "./src/testvte".

[Boris Gjenero (boris-gjenero)]

I'm not able to reproduce this now in Zesty with gnome-terminal 3.20.2-1ubuntu8. Program that was causing problems before is DOSBox SVN with ncursesw output added, https://github.com/dreamlayers/em-dosbox/tree/contxt-only but that works fine now. infocmp $TERM shows I'm using /lib/terminfo/x/xterm-256color and bce is present there, so it seems bce now works.

[Egmont Koblinger (egmont-gmail)]

VTE's behavior definitely didn't change here since you reported the bug. If the issue disappeared, it could've been a change in dosbox or ncurses, or some other magic. Dunno.

[Boris Gjenero (boris-gjenero)]

I tried installing some old libraries and binaries from Yakkety but even with that I couldn't reproduce it in Ubuntu 17.04. I don't have any more Yakkety systems to test on. I also can't reproduce it in 16.04.2 LTS in Windows 10. I don't think any DOSBox changes could have changed this either. So I'm a bit mystified here. Sorry about wasting your time.

[Egmont Koblinger (egmont-gmail)]

You did not waste my time at all... in fact quite the opposite, you finally made me return to that issue with the "le" editor that I had introduced and hopefully fix that, so thanks! :)

[dino99 (9d9)]

This is an unsupported release now. Please think to install the next LTS 'Bionic 18.04'

http://cdimage.ubuntu.com/ubuntu-next/daily-live/current/
https://www.omgubuntu.co.uk/2018/02/ubuntu-18-04-minimal-install-option