Setting titles to be a multiple of \baselineskip fo grid typesetting

Question

I want to typeset my document on grid, so I use the following commands for titles:

\titleformat{\section}
{\fontsize{20}{2\baselineskip}\selectfont\bfseries\sffamily}{}{0em}{#1}
\titlespacing*{\section}{0pt}{0pt}{0pt}

But something fails

How can I fix this?

Full MWE:

\documentclass[10pt,twocolumn]{book}
\usepackage{calc}
\usepackage{geometry}
\usepackage{ragged2e}
\usepackage[explicit]{titlesec}
\usepackage{lipsum}

\usepackage{fontspec}
\setmainfont{Cambria}
\setsansfont{Calibri}

\pagestyle{empty}

\geometry{showframe}

\setlength{\parskip}{0pt}

\titleformat{\section}
{\fontsize{20}{2\baselineskip}\selectfont\bfseries\sffamily}{}{0em}{#1}
\titlespacing*{\section}{0pt}{0pt}{0pt}

\begin{document}

    \raggedbottom\RaggedRight

    \section{First section}

    \lipsum

\end{document}

Answer 1

The macro \inspace takes something that normally doesn't fit into an fixed number of lines and overlays it over a fixed number of lines. You can specify the number of lines, or it can compute them based on the size of the box. The options t/c/b align the tops/centers/bottoms of the box and the reserved space. (Anything except t and b is treated as c.)

It should be noted that the first \section was much larger than the second.

\documentclass[10pt,twocolumn]{book}
\usepackage{calc}
\usepackage{geometry}
%\usepackage{ragged2e}
\usepackage[explicit]{titlesec}
\usepackage{lipsum}

\usepackage{fontspec}
\setmainfont{Cambria}
\setsansfont{Calibri}

\usepackage{everypage}
\usepackage{tikzpagenodes} 
\AddEverypageHook{%
  \begin{tikzpicture}[overlay,remember picture]
    \draw[color=red,very thin]
      (current page text area.south west) grid[step=\normalbaselineskip] 
      (current page text area.north east);
  \end{tikzpicture}%
}

\pagestyle{empty}

\geometry{showframe}

\setlength{\parskip}{0pt}

\newcommand{\inspace}[3][c]% #1 = t/c/b (optional), #2 = number of lines (0=compute), #3 = contents
{\bgroup
  \setbox0=\vbox{#3}%
  \count1=#2\relax
  \def\test{#1}%
  \ifnum\count1<1
    \dimen0=\dimexpr \ht0+\dp0\relax
    \count1=\numexpr \dimen0/\baselineskip\relax
  \fi
  \dimen0=\baselineskip
  \multiply\dimen0 by \count1
  \ifvmode
    \noindent
    \let\terminate=\par
  \else
    \newline
    \let\terminate=\newline
  \fi
  \def\opt{t}% align to top
    \ifx\test\opt\relax
    \strut\rlap{\raisebox{\dimexpr \ht\strutbox-\ht0}[0pt][0pt]{\usebox0}}\terminate
  \else
    \def\opt{b}% align to bottom
    \ifx\test\opt\relax
      \strut\rlap{\raisebox{\dimexpr \ht\strutbox+\dp0-\dimen0}[0pt][0pt]{\usebox0}}\terminate
    \else% anything else is centered
      \strut\rlap{\raisebox{\dimexpr \ht\strutbox-0.5\ht0+0.5\dp0-0.5\dimen0}[0pt][0pt]{\usebox0}}\terminate
    \fi
  \fi
  \loop\ifnum\count1>1
    \advance\count1 by -1
    \strut\terminate
  \repeat
\egroup}


\begin{document}

    \raggedbottom%\raggedright

    \inspace[b]{3}{\section{First section}}

    \lipsum[1-4]

    \inspace[b]{3}{\section{Second section}}

    \lipsum[5-7]

\end{document}