[NTG-context] help with facing page image

[jbf]

Special thanks to Sreeram, Wolfgang, Bruce, Hraban for help with this 
issue, ranging from the simplest 'manual' approach (Bruce) to one that I 
must confess I could never have thought of using: definepageinjection 
(Wolfgang). Needless to say, all contributions work, with a bit of 
adjustment in each case for my particular situation.

The one common factor in all four contributions is the use of setups, so 
a light has begun flashing for me: setups are such an important feature 
of ConTeXt for solving many problems!

Thanks to all,

Julian

On 7/3/22 18:01, śrīrāma wrote:
> On Monday, March 7, 2022 11:50 AM jbf wrote:
>> All ten images are different, though, in my case (Chapter1.jpg,
>> Chapter2.jpg... Chapter10.jpg all in a pics directory, so I'd point
>> \setupexternalfigures to that). I wonder if there is a way to list them
>> so that they get called in order as chapters proceed. A kind of "if such
>> and such then \setlayer 1,2,3...."
> I think that should be easy. Suppose you have images
> {chap-cover-1.jpg, chap-cover-2.jpg,  ... chap-cover-10.jpg}
> each of which appear at the ends of their respective chapters, then the following achieves what you want (once you point ConTeXt to the right directory for figures of course):
>
> % kate: hl ctx
> %%% SOF
>    \setuppagenumbering[alternative=doublesided]
>
>    \definelayer
>      [chapCover]
>      [x=0mm,
>       y=0mm,
>       width=\paperwidth,
>       height=\paperheight,repeat=yes]
>
>    \startsetups chapter:before
>    \doifoddpageelse{}
>      {\pushbackground[page]
>       \resetlayer[chapCover]
>       \setlayer
>       [chapCover]
>       {\determineheadnumber[chapter]
>        \externalfigure
>          [chap-cover-\currentheadnumber]
>          [width=\paperwidth]}
>        \setupbackgrounds[page][background=chapCover]
>        \page[empty]
>        \popbackground}
>    \stopsetups
>
>    \startsetups chapter:after
>    \doifoddpageelse{}
>      {\page[empty]}
>    \stopsetups
>
>    \setuphead
>      [chapter]
>      [page=yes,
>       before=\directsetup{chapter:before},
>       aftersection=\directsetup{chapter:after}]
>
>    \starttext
>    \dorecurse{10}{
>      \startchapter[title={Chapter \convertnumber{word}{\recurselevel}}]
>        \input knuth
>        \ifnum\headnumber[chapter]=5
>        {\bfd five}
>        \fi
>        \blank
>        \input tufte
>        \blank
>        \input ward
>        \blank
>        \ifnum\recurselevel=5
>          \page
>          \input zapf
>          \input zapf
>        \fi
>      \stopchapter
>    }
>    \stoptext
> %%% EOF
>
> So we figure out which chapter we are in and then set the layer to the corresponding picture. Personally, I much prefer to collect all the images into a separate PDF with:
>
> %%% chap-covers.tex
>      \starttext
>      \dorecurse{10}{\startTEXpage
>      \externalfigure[chap-cover-\recurselevel]
>      \stopTEXpage}
>      \stoptext
> %%% EOF
>
> [and get 'chap-covers.pdf' from context]
>
> ... and then modify the 'before' setup to read as below
>
> %%%
>    \startsetups chapter:before
>    \doifoddpageelse{}
>      {\pushbackground[page]
>       \resetlayer[chapCover]
>       \setlayer
>       [chapCover]
>       {\determineheadnumber[chapter]
>        \externalfigure
>          [chap-covers]
>          [page=\currentheadnumber,width=\paperwidth]}
>        \setupbackgrounds[page][background=chapCover]
>        \page[empty]
>        \popbackground}
>    \stopsetups
> %%%
>
> Sreeram
>
>