Document layout and layers/Layers/Alternating backgrounds and repeating layers

I was in need of adding a watermark to the background of a book. Left and right pages needed a different watermark. I also needed the ability to position the watermark anywhere on the page. Through a nice discussion on mailing list Hans was able to make clear how to go about this.

In my final usage of the code below, I changed the preset to bottomleft/bottomright and added hoffset/voffset values to position the text where I wanted it. The solution below would also allow for placing images in the background instead of text.

• \definepapersize[sheet][width=156mm,height=74mm]
  \setuppapersize[A8][sheet]
  \setuppaper[nx=3,ny=1]
  \setuparranging[XY]
  \showframe[edge]
  \setuppagenumbering
   [alternative=doublesided]
  
  \setupcolors
   [state=start]
  
  \setupbackgrounds
   [leftpage]
   [background=Watermark-Left]
  
  \setupbackgrounds
   [rightpage]
   [background=Watermark-Right]
  
  \definelayer
   [Watermark-Left]
   [repeat=yes,
    width=\paperwidth,
    height=\paperheight]
  
  \definelayer
   [Watermark-Right]
   [repeat=yes,
    width=\paperwidth,
    height=\paperheight]
  
  \setlayerframed
   [Watermark-Left]
   [preset=middle]
   [foregroundcolor=middlemagenta,
    frame==off]
   {\scale[sx=2,sy=2]{\rotate[rotation=20.0]{left page watermark}}}
  
  \setlayerframed
   [Watermark-Right]
   [preset=middle]
   [foregroundcolor=middlemagenta,
    frame==off]
   {\scale[sx=2,sy=2]{\rotate[rotation=-20.0]{right page watermark}}}
  
  \starttext
     \chapter{first}  \dorecurse{30}{\input tufte  }
  \stoptext
  

• 

For a somewhat different example, see Draft Watermark