Re: [NTG-context] help with facing page image

8 Mar 2022

      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