White lines between colored cells when using partial vline or hline

[jtl5770]

Using texlive 2021, and tabularray 2022A.

My MWE

\documentclass[11pt]{article}
\usepackage{xcolor}
\usepackage{tabularray}

\definecolor{colA}{rgb}{0.8,0.9,0.8}
\definecolor{colB}{rgb}{0.5,0.7,0.5}
\definecolor{colC}{rgb}{0.95,0.85,0.6}
\definecolor{colD}{rgb}{0.9,0.5,0.5}

\begin{document}
\begin{tblr}{
    column{1} = {colA}, column{2} = {colB}, column{3} = {colC},
    cell{1}{1,3} = {colD}, cell{2}{3} = {colD}, cell{3}{2} = {colD},
    hline{1} = {1,3}{solid}, hline{2} = {1}{solid}, hline{3,4} = {2}{solid}, hline{3} = {3}{solid},
    vline{1,2} = {1}{solid}, vline{4} = {1,2}{solid}, vline{2} = {3}{solid}, vline{3}, 
    %%%%%%%% Note the ugly white lines.
    %%%%%%%% I would like to NOT have to do the following to fix this (but instead it being "right" automatically):
    % hline{2} = {2}{colB, leftpos=0, rightpos=0}, hline{2} = {3}{colD, leftpos=0, rightpos=0}, hline{3} = {1}{colA},
    % vline{2} = {2}{colB},
  }
  Alpha & Beta & Gamma \\
  One   & Two  & Three \\
  Tic   & Tac  & Toe
\end{tblr}
\end{document}

This yields the following result.

See the comments in the MWE what I do to fix this - basically it boils down to having to insert rules colored like the background of the cells and inserting leftpos/rightpos=0 in strategic places. So it is possible, but it seems incredibly awkward having to do this in the first place. Ideally this would be handled in a way that these white lines are not created in the first place.

How could this be done? I have no idea how to do it in a current model where the vline/hline takes up space on its own next to the cells. But - could we implement vlines/hlines (maybe with their own new name and semantic) that actually don't take up space, but are rather printed on top? Half of the width of the rule would then be added to the cell right (or top in the case of a hline) and half of it to the cell left (or bottom), so the visible part of the cell would still be exactly the same as it would be without the rule in place. This would ensure that the cells are always directly stacked next to each other and the background wouldn't have any discontinuities.

[lvjr]

In the future there will be a tikz library (see #29) and you can draw borders on the cells with tikz commands.

[jtl5770]

Using tikz seems like the obvious answer, but isn't it a bit like cheating :-) ?
For the second half of my suggestion (the automatic enlargement of the cell with padding) - could this be implemented in the tikz case at all?

[jtl5770]

Actually, for vertical lines I wonder if it would be ok to just use something like \clap to make them take up no space... but I didn't find a way to insert it for vlines. And I have no idea if something similar exists to smash vertical space, too. Sorry, but my TeX knowledge is very basic, so I don't think I can implement this myself without help :-)

[lvjr]

I haven't decided how and when to handle this. But at lease I don't think enlarging cell sizes is a good idea. It will probably break other things.

[jtl5770]

Yes, I understand that. If needed, I assume this can be easily done manually, by choosing e.g. rowsep accordingly.
This will be much less of a problem than having to hunt the white lines and filling them with colored v/hlines manually. I have a real-life use case with a complicated 12x13 table with non-continuous lines where the code to fix the white lines is around the same size as all the rest :-)
Well, anyway - as I won't be of any help in coding I can at least offer my help in beta testing anything you may come up with, whenever that may be.

[lvjr]

Actually, for vertical lines I wonder if it would be ok to just use something like \clap to make them take up no space... but I didn't find a way to insert it for vlines. And I have no idea if something similar exists to smash vertical space, too. Sorry, but my TeX knowledge is very basic, so I don't think I can implement this myself without help :-)

In general, it is doable to make hlines and vlines take up no space. But I think we only need to support single hline/vline, as double hlines/vlines look weird. Also don't expect the new feature will arrive soon.

Update: the new interface could be

rules={smash}

see also issues #102 and #172.

[jtl5770]

Is there any update on this topic? Something like the proposed rules={smash}? Although I still think - the current default behavior for partial v/hlines is practically never the intended outcome. Sure, as most use cases don't involve colored cell backgrounds, it also almost never is a problem for anybody, but as soon as you are forced to combine colored cells (or rows, columns) using partial rules is for sure producing something that you didn't want to see. Being forced then to change the whole behavior of rules from taking up space to NOT taking up space seems not satisfactory to me. Again - if the rule width is only the default, it will most probably not result in any problems, but if the rules are e.g. 5pt width, it will most certainly interfere with the contents of the cells, won't it? Essentially you would then need to add extra padding manually.

For me it would feel naturally if cells without a rule between them would never leave a gap between them automatically, while the minimum padding between cell borders and content would always be preserved, regardless of the fact of there being a rule or not (essentially increasing the padding for cells without rules if they are in the same row or column with cells having a partial rule)