I've updated the KDE3 kvkbd build to include further patches developed for the TDE version. The URL is the same as for the Nov '20 posting - https://ray-v.github.io/KDE3-kvkbd-patches.tar.xz.
Enhancements include: Added ColorDialog for user setting keyboard and key colours Tooltips I18n support Added levels 3 & 4 [AltGr AltGr+Shift] characters display
On most physical keyboards there is a very limited number of level 3 & 4 characters shown [on the right of the key]. Kvkbd shows all the characters available when AltGr or AltGr+Shift is clicked. Keyboard selection is immediate using either the KDE keyboard tool or setxkbmap and can therefore be toggled to any other layout to insert any other character from an alternative layout.
Alternatively, create your own symbols file with the characters you would want in the level 3 & 4 positions. This has been done with this mathematical symbols file which is the us [basic] layout with mathematical characters and level3(ralt_switch) added: https://github.com/CaptchaSamurai/Math-Unicode-keyboard-overlay-Linux-XKB/ra...
Loading this [mth] with the KDE keyboard tool or setxkbmap will enable the mathematical symbols to be seen by clicking on AltGR or AltGr+Shift, rather than having to know where they are on a physical keyboard. Kvkdb works with the physical keyboard, so the character can be printed from either.
The patches have been mostly left as they developed and are commented so can be included or not for any particular feature.