Change chapters heading (#173)

* Implement kaobook style chapter headings

Now supports several style of chapters
- plain (default koma)
- bar adds a gray bar
- lines (a box around it)
- kao

This is totally _inspired_ by the kaobook template:
https://github.com/fmarotta/kaobook/

* Use lines style for chapter by default

As Hendrik indicated...

book/sourdough.sty

@@ -10,6 +10,7 @@
 \usepackage{makecell}
 \usepackage[mode=match, reset-text-family=false]{siunitx}
 \usepackage{fontspec}
+\usepackage{calc}
 
 \renewcommand\theadfont{\bfseries}
 
@@ -75,5 +76,178 @@
 \usepackage{caption}
 \captionsetup[figure]{font=footnotesize}
 
-
 \DeclareSIUnit\degF{\text{°}F}
+
+%-----------------------------------------------------------------------------
+%    KAO CHAPTER HEADING STYLES
+%-----------------------------------------------------------------------------
+
+\newlength{\hscale}
+\newlength{\vscale}
+\newlength{\mtocshift}
+
+% By default, the scales are set to work for a4paper
+\setlength{\hscale}{1mm}
+\setlength{\vscale}{1mm}
+
+\newif\ifwidelayout%
+\def\IfWideLayout{%
+    \ifwidelayout%
+        \expandafter\@firstoftwo%
+    \else%
+        \expandafter\@secondoftwo%
+    \fi%
+}
+
+% Command to easily switch between chapter styles
+\DeclareDocumentCommand{\setchapterstyle}{m}{%
+    \ifthenelse{\equal{plain}{#1}}{\chapterstyleplain}{}
+    \ifthenelse{\equal{bar}{#1}}{\chapterstylebar}{}
+    \ifthenelse{\equal{lines}{#1}}{\chapterstylelines}{}
+    \ifthenelse{\equal{kao}{#1}}{\chapterstylekao}{}
+}
+
+% The default definition in KOMA script
+\DeclareDocumentCommand{\chapterstyleplain}{}{%
+    \renewcommand{\chapterlinesformat}[3]{%
+        \@hangfrom{##2}{##3}}
+    \renewcommand*{\chapterformat}{%
+        \mbox{\chapappifchapterprefix{\nobreakspace}\thechapter%
+        \autodot\IfUsePrefixLine{}{\enskip}}}
+    \RedeclareSectionCommand[beforeskip=0cm,afterskip=10\vscale]{chapter}
+    \setlength{\mtocshift}{-1\vscale}
+}
+
+% Gray bar
+\DeclareDocumentCommand{\chapterstylebar}{}{%
+    \renewcommand*{\chapterformat}{%
+        \mbox{\chapappifchapterprefix{\nobreakspace}\thechapter%
+        \autodot\IfUsePrefixLine{}{\enskip}}%
+    }
+    \renewcommand{\chapterlinesformat}[3]{%
+        \begin{tikzpicture}[remember picture, overlay]
+            \node[
+                anchor=south west,
+                xshift=\dimexpr - \hoffset - \oddsidemargin - 1in -1mm,%-30\hscale,
+                yshift=4.3mm,
+                rectangle,
+                fill=gray!20!white,
+                fill opacity=0.8,
+                inner ysep=5\vscale,
+                inner xsep=\dimexpr \hoffset + \oddsidemargin + 1in,%30\hscale,
+                text opacity=1,
+                text width=\paperwidth-40\hscale,
+            ]{\@hangfrom{##2}{##3}};
+        \end{tikzpicture}
+    }
+    \RedeclareSectionCommand[beforeskip=-55\vscale,afterskip=6\vscale]{chapter}
+    \setlength{\mtocshift}{-1\vscale}
+}
+
+% Lines
+\renewcommand{\hrulefill}[1][0.4pt]{%
+    \leavevmode\leaders\hrule height #1\hfill\kern\z@%
+}
+
+\DeclareDocumentCommand{\chapterstylelines}{}{%
+    \renewcommand*{\chapterformat}{%
+        \chapappifchapterprefix{\nobreakspace}\scalebox{3.5}{\thechapter\autodot}%
+    }%
+    \renewcommand\chapterlinesformat[3]{%
+        %\vspace*{-1cm}%
+        \leavevmode%
+        \makebox[0pt][l]{%
+        \makebox[\textwidth][l]{\hrulefill[1pt]##2}%\hfill%\par%\bigskip
+        \makebox[\marginparsep][l]{}%
+        \makebox[\marginparwidth][l]{}%
+        }\\
+        %\vspace{.5cm}
+        \makebox[0pt][l]{%
+        \makebox[\textwidth][l]{##3}%
+        \makebox[\marginparsep][l]{}%
+        \makebox[\marginparwidth][l]{}%
+        }\\
+        \makebox[0pt][l]{%
+        \makebox[\textwidth+\marginparsep+\marginparwidth][l]{\hrulefill[1.1pt]}%
+    }%
+    \RedeclareSectionCommand[beforeskip=0cm,afterskip=10\vscale]{chapter}
+    \setlength{\mtocshift}{-1\vscale}%
+}
+}
+% The Kao style
+\DeclareDocumentCommand{\chapterstylekao}{}{%
+    \IfWideLayout{%
+        \renewcommand*{\chapterformat}{%
+            \mbox{\chapappifchapterprefix{\nobreakspace}\scalebox{2.85}{\thechapter\autodot}}%
+        }%
+        \renewcommand\chapterlinesformat[3]{%
+            \vspace{3.5\vscale}%
+            \if@twoside%
+                \Ifthispageodd{%
+                    \smash{\makebox[0pt][l]{%
+                        \parbox[b]{\textwidth - 6.2\hscale}{\flushright{##3}}%
+                        \makebox[6.2\hscale][c]{\rule[-2\vscale]{1pt}{27.4\vscale+\f@size mm}}%
+                        \parbox[b]{\marginparwidth}{##2}%
+                    }}%
+                }{
+                    \smash{\makebox[\textwidth + 6.2\hscale][r]{%
+                        \parbox[b]{47.7\hscale + 6.2\hscale}{\flushright{##2}}%
+                        \makebox[6.2\hscale][c]{\rule[-2\vscale]{1pt}{27.4\vscale+\f@size mm}}%
+                        \parbox[b]{\textwidth}{\flushleft{##3}}%
+                    }}%
+                }
+            \else%
+                \smash{\makebox[0pt][l]{%
+                    \parbox[b]{\textwidth - 6.2\hscale}{\flushright{##3}}%
+                    \makebox[6.2\hscale][c]{\rule[-2\vscale]{1pt}{27.4\vscale+\f@size mm}}%
+                    \parbox[b]{\marginparwidth}{##2}%
+                }}%
+            \fi%
+        }%
+    }{%
+        \renewcommand*{\chapterformat}{%
+            \mbox{\chapappifchapterprefix{\nobreakspace}\scalebox{2.85}{\thechapter\autodot}}%
+        }%
+        \renewcommand\chapterlinesformat[3]{%
+            \vspace{3.5\vscale}%
+            \if@twoside%
+                \Ifthispageodd{%
+                    \smash{\makebox[0pt][l]{%
+                        \parbox[b]{\textwidth}{\flushright{##3}}%
+                        \makebox[\marginparsep][c]{\rule[-2\vscale]{1pt}{27.4\vscale+\f@size mm}}%
+                        \parbox[b]{\marginparwidth}{##2}%
+                    }}%
+                }{
+                    \smash{\makebox[\textwidth][r]{%
+                        \parbox[b]{\marginparwidth}{\flushright{##2}}%
+                        \makebox[\marginparsep][c]{\rule[-2\vscale]{1pt}{27.4\vscale+\f@size mm}}%
+                        \parbox[b]{\textwidth}{\flushleft{##3}}%
+                    }}%
+                }
+            \else%
+                \smash{\makebox[0pt][l]{%
+                    \parbox[b]{\textwidth}{\flushright{##3}}%
+                    \makebox[\marginparsep][c]{\rule[-2\vscale]{1pt}{27.4\vscale+\f@size mm}}%
+                    \parbox[b]{\marginparwidth}{##2}%
+                }}%
+            \fi%
+        }%
+    }%
+    \RedeclareSectionCommand[beforeskip=0cm,afterskip=10\vscale]{chapter}%
+    \setlength{\mtocshift}{-3.5\vscale}%
+}
+
+% Takes as input the image path and optionally the "beforeskip"
+\DeclareDocumentCommand{\setchapterimage}{O{55\vscale} m}{%
+    \setchapterpreamble[o]{%
+        \vspace*{-27\vscale}\hspace*{\dimexpr - \hoffset - \oddsidemargin - 1in}%
+        \includegraphics[width=\paperwidth,height=#1+27\vscale,keepaspectratio=false]{#2}%
+    }%
+    \chapterstylebar%
+    % beforeskip=-(figure_height-top_margin)
+    \RedeclareSectionCommand[beforeskip=-#1, afterskip=6\vscale]{chapter}%
+    \setlength{\mtocshift}{0cm}%
+}
+
+% By default start with the kao style
+\setchapterstyle{lines}