[NTG-context] help with facing page image

[śrīrāma]

On Thursday, March 10, 2022 3:32 AM jbf via ntg-context wrote:
> Am endeavouring to explore Wolfgang's very 'elegant' solution to this 
> facing page challenge. The exploration has included a look at 
> base/mkxl/page-inj.mklx (thanks Sreeram for reminding me of this) where 
> I see immediately that the approach is experimental and where it says 
> also that 'probably more alternatives will be added'. I wonder if that 
> last phrase also includes the ability to manipulate the image(s) either 
> generally or in individual cases?
> 

The following example is based on Wolfgang's solution using injections: I have modified the setup slightly to hook into \externalfigure's {width, height, orientation} using user-variables. With this I think you can place any kind of image (portrait or landscape) correctly by using width, height, and rotation.

I picked up some images of cows, 'spider', 'hacker' and 'mill' and have them renamed as {chap-cover-1, ... chap-cover-6} for a total of 6 chapter images.

%%% start example
   \definepageinjectionalternative
   [chapter:image]
   [renderingsetup=pageinjection:chapter:image]

   \startsetups [pageinjection:chapter:image]
   \clip
      [width=\framedwidth,height=\framedheight]
      {\centerbox{%
         \externalfigure
            [\dummyparameter{name}]
            [%factor=,
             width=\structureuservariable{width},
             height=\structureuservariable{height},
             orientation=\structureuservariable{rotation}]%
      }}
   \stopsetups

   \definepageinjection
   [chapter:start]
   [empty]
   [page=left]

   \definepageinjection
   [chapter:insert]
   [previouspage]
   [alternative=chapter:image,
      pagestate=stop]

   \setuphead
   [chapter]
   [beforesection={\pageinjection[chapter:start]},
      insidesection={\pageinjection[chapter:insert][name=\structureuservariable{image}]}]

   \setuphead
   [chapter]
   [beforesection={\pageinjection[chapter:start]},
      insidesection={\pageinjection[chapter:insert][name={chap-cover-\namedheadnumber{chapter}}]}]


   \setuppagenumbering
   [alternative=doublesided]

   \setupexternalfigures
   [location=default]

   \starttext
      \startchapter [title={Mill}] [rotation=90,width=\paperheight]
      \dorecurse{7}{\samplefile{lorem}}
      \stopchapter

      \startchapter [title={Mill}] [rotation=-90,width=\paperheight]
      \dorecurse{11}{\samplefile{lorem}}
      \stopchapter

      \startchapter [title={Mill}] [rotation=-90,width=\paperheight]
      \dorecurse{7}{\samplefile{lorem}}
      \stopchapter

      \startchapter [title={Mill}] [rotation=90,width=\paperheight]
      \dorecurse{7}{\samplefile{lorem}}
      \stopchapter

      \startchapter [title={Mill}] [rotation=-45,width=\paperwidth]
      \dorecurse{11}{\samplefile{lorem}}
      \stopchapter

      \startchapter [title={Mill}] [height=\paperheight]
      \dorecurse{7}{\samplefile{lorem}}
      \stopchapter
   \stoptext
%%% end example

Sreeram