Add vertical spacing into list of figures for each section (scrartcl)

Question

I have found several posts and questions from people wanting to remove the vertical spacing automatically added to the list of figures, but my problem is (exactly) the opposite:

I'm using the scrartcl document class with sections as the highest level seperator. In my list of figures there is no separation between the figures of different sections.

How can I add such a visual separation?

See the following minimal working example and the output below:

\documentclass[11pt,a4paper]{scrartcl}

\usepackage{amsmath}

\numberwithin{figure}{section}

\begin{document}

\listoffigures

\section{Section}

\begin{figure}[ht]\caption{Figure}\end{figure}
\begin{figure}[ht]\caption{Figure}\end{figure}

\section{Section}

\begin{figure}[ht]\caption{Figure}\end{figure}

\end{document}

Answer 1

You need to patch the \@startsection command; patching \section is also possible, but it would add a spacing command also for \section*. Not a big deal, but if it's possible to avoid it, the better.

\documentclass[11pt,a4paper]{scrartcl}

\usepackage{amsmath}
\usepackage{etoolbox}

\makeatletter
\patchcmd{\@startsection}
  {\@dblarg}
  {\artemis@space@loft{#2}\@dblarg}
  {}{}
\newcommand{\artemis@space@loft}[1]{%
  \ifnum#1=\sectionnumdepth
    \doforeachtocfile[float]{%
      \addtocontents{\@currext}{\protect\addvspace{\@sectionlistsgap}}%
    }%
  \fi
}
\newcommand{\@sectionlistsgap}{5pt} % <-- change here the desired gap
\makeatother

\numberwithin{figure}{section}

\begin{document}

\listoffigures

\section{Section}

\begin{figure}[ht]\caption{Figure}\end{figure}
\begin{figure}[ht]\caption{Figure}\end{figure}

\section{Section}

\subsection{SUB}

\begin{figure}[ht]\caption{Figure}\end{figure}

\end{document}

Explanation: \@dblarg is executed only when we have \section without *; so, before TeX executes it, we add \artemis@space@loft, that adds a vertical space annotation in the .lof and .lot files. This is the same as the book class does for \chapter (10pt is used there, in an article a smaller space seems more appropriate). It uses a technique suggested by Johannes_B that exploits a feature of Koma-Script; in this way also newly defined float types will get the same treatment.

Parameter #2 to \@startsection is the section level, so we check it's the same as \sectionnumdepth. For article one should use \@ne instead of \sectionnumdepth in the body of \artemis@space@loft.

I added \subsection in order to check that the spacing is added only for sections (and it is).

Important update for KoMaScript version 3.14

When the newly released version 3.14 of KoMaScript classes and packages has been installed, the above patch doesn't work any more.

For this version one has to change

\patchcmd{\@startsection}
  {\@dblarg}
  {\artemis@space@loft{#2}\@dblarg}
  {}{}

into

\patchcmd{\scr@startsection}
  {\scr@section@dblarg}
  {\artemis@space@loft{#2}\scr@section@dblarg}
  {}{}

Thanks to Johannes_B for having noticed it so early (the new version was uploaded in TeX Live on December 8, 2014).

If both patches are necessary for a cooperative job when one of the parties has not yet updated KoMaScript, then

\makeatletter
\ifdefined\scr@startsection
  \patchcmd{\scr@startsection}
    {\scr@section@dblarg}
    {\artemis@space@loft{#2}\scr@section@dblarg}
    {}{}
\else
  \patchcmd{\@startsection}
    {\@dblarg}
    {\artemis@space@loft{#2}\@dblarg}
    {}{}
\fi
\newcommand{\artemis@space@loft}[1]{%
...

should do.