How to Test for Page Style Inside eso-pic

Question

I'm having trouble implementing this solution inside eso-pic: If pagestyle equal to... -- How should I ask it? It looks like \thepagestyle is coming out equal to "fancy" on every page, including obviously and explicitly "plain" pages.

\documentclass[12pt,twoside]{book}
\usepackage[paperwidth=4in,paperheight=2in,left=0.5in,top=0.25in,%
  right=0.25in,bottom=0.25in]{geometry}
\usepackage{fancyhdr}
\usepackage{etoolbox}
\usepackage{eso-pic}
\makeatletter
\pretocmd{\pagestyle}{%
  \gdef\@regularpagestyle{#1}%
  \gdef\thepagestyle{\if@specialpage\@specialstyle\else\@regularpagestyle\fi}
  }
{\message{(patching of \string\pagestyle\ succeeded)}}
{\message{(patching of \string\pagestyle\ failed)}}
\makeatother
\pagestyle{fancy}
\begin{document}
\AddToShipoutPicture{%
    \fontsize{24.88pt}{24.88pt}\selectfont%
    \ifdef{\thepagestyle}{%
      The page style is `\thepagestyle'.%
    }{%
      There is no page style declared.%
}}
\thispagestyle{plain}
\ifdef{\thepagestyle}{
  The page style is `\thepagestyle'.%
}{%
  There is no page style declared.
}
\end{document}

My goal is to set different background images for each page style. I can either set a continuing default (using \AddToShipoutPicture), or a single page (using \AddToShipoutPicture*), but not both.

Using them concurrently gives terrible results. Clearing the default for a single page leaves no way to set the default again, unless I know exact page boundaries.

The solution here would be a terrible cop-out imho: How to clear the background of just the current page? It would result in a bloated filesize and low quality internal data.

Right now I'm trying to put all the logic in a single call to \AddToShipoutPicture (in my custom command \PageDecor):

\documentclass[10pt,twoside]{book}
\usepackage[paperwidth=6in,paperheight=9in,left=1in,top=1in,right=0.75in,bottom=1in]{geometry}
\usepackage{fancyhdr}
\renewcommand{\headrulewidth}{0pt}
\usepackage{graphicx}
\usepackage{etoolbox}
\usepackage{ifthen}


\makeatletter
\pretocmd{\pagestyle}{
  \gdef\@regularpagestyle{#1}
  \gdef\thepagestyle{\if@specialpage\@specialstyle\else\@regularpagestyle\fi}
  }
{\message{(patching of \string\pagestyle\ succeeded)}}
{\message{(patching of \string\pagestyle\ failed)}}
\makeatother


\usepackage{eso-pic}
\newcommand{\PageDecor}{\AddToShipoutPicture{%
    \ifodd\value{page}%
        \ifthenelse{\equal{\thepagestyle}{fancy}}{%
            \includegraphics[width=6in]{decor-6x9-right-fancy.pdf}%
        }{%
            \includegraphics[width=6in]{decor-6x9-right-plain.pdf}%
        }%
    \else%
        \ifthenelse{\equal{\thepagestyle}{fancy}}{%
            \includegraphics[width=6in]{decor-6x9-left-fancy.pdf}%
        }{%
            \includegraphics[width=6in]{decor-6x9-left-plain.pdf}%
        }%
    \fi%
}}
\newcommand{\PageDecorFancyOnce}{\AddToShipoutPicture*{%
    \ifodd\value{page}%
        \includegraphics[width=6in]{decor-6x9-right-fancy.pdf}%
    \else%
        \includegraphics[width=6in]{decor-6x9-left-fancy.pdf}%
    \fi%
}}
\newcommand{\PageDecorPlainOnce}{\AddToShipoutPicture*{%
    \ifodd\value{page}%
        \includegraphics[width=6in]{decor-6x9-right-plain.pdf}%
    \else%
        \includegraphics[width=6in]{decor-6x9-left-plain.pdf}%
    \fi%
}}
\begin{document}

\pagestyle{fancy}
\pagenumbering{arabic}
\setcounter{page}{1}
\fancypagestyle{plain}{\fancyhf{} \cfoot[\thepage]{\thepage}}
\fancyhf{}
\lhead[{\makebox[0.25in][l]{\hfill\thepage\hfill}}]{}
\rhead[]{{\makebox[0.25in][r]{\hfill\thepage\hfill}}}
\PageDecor

\thispagestyle{plain}
Testing testing 0123456789
\clearpage
\thispagestyle{plain}
Testing testing 0123456789
\clearpage
Testing testing 0123456789
\clearpage
Testing testing 0123456789

\end{document}

I can simulate my desired output here only because I know every page boundary:

%\PageDecor

\thispagestyle{plain}
\PageDecorPlainOnce
Testing testing 0123456789
\clearpage
\thispagestyle{plain}
\PageDecorPlainOnce
Testing testing 0123456789
\clearpage
\PageDecorFancyOnce
Testing testing 0123456789
\clearpage
\PageDecorFancyOnce
Testing testing 0123456789

I'm afraid I just don't understand Matthew Leingang's modifications well enough to troubleshoot them myself. I've searched for definitions to these symbols \if@specialpage, etc. to no avail. It remains entirely a black box for me.

Any help or insight would be appreciated.

Answer 1

The following provides an interface for page style-specific backgrounds:

\documentclass[twoside]{book}

\usepackage{fancyhdr,graphicx,afterpage,eso-pic}
\renewcommand{\headrulewidth}{0pt}

\let\oldpagestyle\pagestyle
\let\oldthispagestyle\thispagestyle
\renewcommand{\pagestyle}[1]{% Update \pagestyle{<style>}...
  \gdef\thepagestyle{#1}% ...to store <style> in \thepagestyle
  \oldpagestyle{#1}}
\renewcommand{\thispagestyle}[1]{% Update \thispagestyle{<style>}...
  \xdef\savepagestyle{\thepagestyle}% ...to store <style> in \thepagestyle ...
  \gdef\thepagestyle{#1}%
  \afterpage{\xdef\thepagestyle{\savepagestyle}}% ...and revert to original <style> after this page
  \oldthispagestyle{#1}}

\newcommand{\PageDecor}{\AddToShipoutPicture{%
  \ifodd\value{page} % Odd page
    \ifnum\pdfstrcmp{\thepagestyle}{fancy} = 0 % Page style is fancy
      \AtPageCenter{\makebox[0pt]{\raisebox{-.5\height}{\scalebox{10}{FO}}}}
    \else% \thepagestyle = \pagestyleplain (or another page style)
      \AtPageCenter{\makebox[0pt]{\raisebox{-.5\height}{\scalebox{10}{PO}}}}
    \fi
  \else% Even page
    \ifnum\pdfstrcmp{\thepagestyle}{fancy} = 0 % Page style is fancy
      \AtPageCenter{\makebox[0pt]{\raisebox{-.5\height}{\scalebox{10}{FE}}}}
    \else% \thepagestyle = \pagestyleplain (or another page style)
      \AtPageCenter{\makebox[0pt]{\raisebox{-.5\height}{\scalebox{10}{PE}}}}
    \fi
  \fi
}}

\fancyhf{}% Clear header/footer
\lhead[\thepage]{}% Odd left header
\rhead[]{\thepage}% Even right header
\fancypagestyle{plain}{%
  \fancyhf{}% Clear header/footer
  \cfoot[\thepage]{\thepage}% Center footer (odd & even)
  \gdef\thepagestyle{plain}}

\begin{document}

\pagestyle{fancy}

\PageDecor

\thispagestyle{plain}
Page 1 (plain page style)
\clearpage
Page 2 (fancy page style)
\clearpage
Page 3 (fancy page style)
\clearpage
\thispagestyle{plain}
Page 4 (plain page style)

\end{document}

We update \pagestyle and \thispagestyle to store the current page style in \thepagestyle and condition accordingly inside \AddToShipoutPicture using the eTeX \pdfstrcmp{<strA>}{<strB>} which returns 0 if <strA> = <strB>.