Mysterious blank page before \chapter using \chapterlinesformat in spite of openany/oneside (KOMA-script)

Question

Each time I produce a new chapter, I want to have a single page with the chapter title at the center of it. Following the KOMA-script documentation, and looking online, I've managed to do it by redefining \chapterlinesformat.

Here is what I don't understand:

• If I use my code to center some content inside the document, everything works fine
• If I use the same code to rewrite \chapterlinesformat, a blank page appears
• So clearly \chapterlinesformat do something just before it writes the chapter.

Online searches quickly told me that a blank page before chapter was usually because of odd/even numbered pages or such, and that a quick fix was to use openany/oneside option. I've tried to look at KOMA-script documentation to understand where this blank page came from, without success.

Here is my MWE:

\documentclass[oneside, openany]{scrbook}
\usepackage{xparse}
\usepackage{blindtext}

\DeclareDocumentCommand\chapterheadstartvskip {}{}
\DeclareDocumentCommand\chapterheadendvskip {}{}

\DeclareDocumentCommand\chapterlinesformat {mmm}
    {
    \clearpage %need to be removed for no blank page before \chapter, why?
    \topskip0pt
    \vspace*{\fill}
    \begin{center}
    #3
    \end{center}
    \vfill
    \clearpage
    }

\begin{document}

\blindtext

% DO NOT PRODUCE BLANK PAGE BEFORE Test
\clearpage
\topskip0pt
\vspace*{\fill}
\begin{center}
Test
\end{center}
\vfill
\clearpage

\blindtext
%BLANK PAGE before Chapter, why?
\chapter{Chapter}

\blindtext

\end{document}

Answer 1

There is no need to redefine \chapterlinesformat. You can simple redefine \chapterheadstartvskip, \chapterheadendvskip, \raggedchapter and \chapterformat to get

\documentclass[oneside]{scrbook}
\usepackage{blindtext}

\renewcommand*\chapterheadstartvskip{\vspace*{-\topskip}\vfill}
\renewcommand*\chapterheadendvskip{\vfill\clearpage}
\renewcommand*\raggedchapter{\centering}
\renewcommand*\chapterformat{}

\begin{document}
\clearpage
\vspace*{-\topskip}
\vfill
\begin{center}
Test
\end{center}
\vfill
\clearpage
\blindtext
\chapter{Chapter}
\blindtext
\end{document}

---

You can redefine \chapterformat to change the layout of the chapter number. Simple example:

\documentclass[oneside]{scrbook}
\usepackage{blindtext}

\usepackage{tikzpagenodes}

\renewcommand*\chapterheadstartvskip{\vspace*{-\topskip}\vfill}
\renewcommand*\chapterheadendvskip{\vfill\clearpage}

\renewcommand*\raggedchapter{\centering}
\renewcommand*\chapterformat{%
  \tikz[remember picture,overlay]
    \path(current page text area.center)node[scale=30,lightgray]{\thechapter};%
}

\begin{document}
\clearpage
\vspace*{-\topskip}
\vfill
\begin{center}
Test
\end{center}
\vfill
\clearpage
\blindtext

\chapter{Chapter}
\blindtext
\end{document}

Result:

Answer 2

The answer to my question is simply that \chapter issues a \clearpage or \cleardoublepage, so since there is already one \clearpage at the beginning in the command I created with \chapterlinesformat, this creates a blank page when I call \chapter

Thanks to campa for the answer.