Support OSC 4 Change Color Number (was: Vis editor)

[travankor]

I'm testing qterminal-git with QT5.14.2. The vis editor is broken on the default settings and shows a blue screen. Typing TERM=screen-256color vis fixes this issue.

I think this affects KDE's Konsole, too.

[travankor]

https://github.com/martanne/vis/wiki/FAQ#my-terminal-colors-are-messed-up-what-is-going-on

Some terminals (e.g. Apple's Terminal.app) incorrectly advertise the "can change color" ccc (seeterminfo(5)) capability, even though they are incapable of performing the requested change. As a result terminal colors end mixed up. Since we start replacing just after the initial 16 colors, this usually has the symptom of the editor appearing in dark blues and greens.

[travankor]

I don't think it's correct to set xterm-256color currently, when xterm handles this correctly.

I think either qterminal should set TERM as konsole-256color by default (or ship a custom terminfo) or correctly change color for curses.

[yan12125]

Thanks for the report. Yep with TERM=xterm-256color, ccc is advertised, but qtermwidget does not respond to Change Color Number (OSC 4) requests. I will try to add support for OSC 4. The long term goal is achieving xterm comaptibility.

[yan12125]

As a side note, after OSC 4, vis uses CSI 38;5 to use indexed color.