How to keep base-line based distance before (tikz) environment?

Question

I have an environment (tikzpicture) that tries to occupy a height equal to the multiple of the current line height / baselineskip (I need this to be pixel-perfect, so in a multicol-setup the baselines match up in all columns before/after the image).

The fixed tikz height itself seems to work, but the environment itself does not keep a correct baseline-based spacing to the preceding paragraph. If letters extend below the baseline (e.g. a 'g'), the gap to the previous baseline is different than without extending characters.

How can I make sure the environment keeps an automatic baseline-based distance to the previous paragraph? I have many many uses of this environment in my document, so I do not want to manually add fixes based on the preceding content.

MWE:

\documentclass[openany]{book}
\usepackage{tikz}
\begin{document}

Test g.

\begin{tikzpicture}[y=\baselineskip]
    \draw (0, 0) -- (0, 4);
\end{tikzpicture}

Test

\begin{tikzpicture}[y=\baselineskip]
    \draw (0, 0) -- (0, 4);
\end{tikzpicture}

Test

\end{document}

Answer 1

This is not related with tikz, but with how TeX make paragraphs. Latex use the rubber length \baselineskip to set the distance between lines (plus \parskip if it is the beginning of a paragraph). But if you add a tikzpicture, or other box that make the line higher, then, if the lines would be too close together, closer than \lineskiplimit, then TeX instead uses \lineskip as the interline glue (see here), and this interline glue takes into account the depth of the previous line.

An example:

\documentclass[openany]{book}
\usepackage{tikz}

\setlength{\fboxsep}{-0.5pt}
\setlength{\fboxrule}{0.5pt}
%\setlength{\lineskip}{0cm}
%\setlength{\parskip}{1pt}

\newcommand{\tikzmark}[1]{\tikz[overlay, remember picture, baseline={(#1.base)}] 
\node[inner sep=0pt, line width=0pt] (#1) {\phantom{Tg}};}

\begin{document}

\fbox{Test}\fbox{g} \tikzmark{A}

\fbox{%
\begin{tikzpicture}[y=\baselineskip]
    \draw (0, 0) -- (1, 4);
\end{tikzpicture}} \tikzmark{B}

\fbox{Test} \tikzmark{C}

\fbox{\begin{tikzpicture}[y=\baselineskip]
    \draw (0, 0) -- (1, 4);
\end{tikzpicture}}

\fbox{Test} \tikzmark{D}

\fbox{Test}\fbox{g} \tikzmark{D2}

\fbox{Test} \tikzmark{D3}

\fbox{Test}

\begin{tikzpicture}[overlay, remember picture, font=\tiny]
    \draw[red] (A.south) -- node[right] {lineskip} ++(down:\lineskip);
    \draw[red, transform canvas={xshift=-0.43cm}] (B.base) -- node[right] {baselineskip} ++(down:\baselineskip);
    \draw[red] (C.base) -- node[right] {lineskip} ++(down:\lineskip);
    \draw[red] (D.base) -- node[right] {baselineskip} ++(down:\baselineskip);
    \draw[red] (D2.base) -- node[right] {baselineskip} ++(down:\baselineskip);
    \draw[red] (D3.base) -- node[right] {baselineskip} ++(down:\baselineskip);
\end{tikzpicture}

\end{document}

You can try remove the depth from the previous line (see here):

\documentclass[openany]{book}
\usepackage{tikz}

\setlength{\fboxsep}{-0.5pt}
\setlength{\fboxrule}{0.5pt}
%\setlength{\lineskip}{0cm}
%\setlength{\parskip}{1pt}

\newcommand{\tikzmark}[1]{\tikz[overlay, remember picture, baseline={(#1.base)}] 
\node[inner sep=0pt, line width=0pt] (#1) {\phantom{Tg}};}
\newcommand{\zerodepth}[1]{\raisebox{0pt}[\height][0pt]{#1}} 

\begin{document}

\fbox{Test}\fbox{\zerodepth{g}}

\fbox{%
\begin{tikzpicture}[y=\baselineskip]
    \draw (0, 0) -- (1, 4);
\end{tikzpicture}} 

\fbox{Test} 

\fbox{\begin{tikzpicture}[y=\baselineskip]
    \draw (0, 0) -- (1, 4);
\end{tikzpicture}}

\end{document}

but this solution is not going to work with whole paragraphs.

EDIT: Another option is add a \strut at the end of the line of paragraph avobe the tikz picture.