%% 
%%  Ein Beispiel der DANTE-Edition
%%  
%%  1. Auflage
%% 
%% 
%%  Copyright (C) 2013 Herbert Voss
%% 
%%  It may be distributed and/or modified under the conditions
%%  of the LaTeX Project Public License, either version 1.3
%%  of this license or (at your option) any later version.
%% 
%%  See http://www.latex-project.org/lppl.txt for details.
%% 
%% 
%% ==== 
% Show page(s) 1
%% 
\input CTdefault.tex
%StartShownPreambleCommands
\startluacode
local format = string.format
local concat = table.concat
function document.TestBitmap(nx,ny)
  nx = math.round(nx/65536)
  ny = math.round(ny/65536)
  nx = 2 * math.round(nx/2)
  ny = 2 * math.round(ny/2)
  local r = { }
  local dx = 255/nx
  local dy = 255/ny
  for i=1,ny/2 do
    local n = i*dy
    local c = { }
    for j=1,nx/2 do    c[#c+1] = format("%02x",j*dx+n) end
    for j=nx/2,1,-1 do c[#c+1] = format("%02x",j*dx+n) end
    c = concat(c,"",1,nx)
    r[#r+1] = c
  end
  for i=ny/2,1,-1 do
    local n = i*dy
    local c = { }
    for j=1,nx/2 do    c[#c+1] = format("%02x",j*dx+n) end
    for j=nx/2,1,-1 do c[#c+1] = format("%02x",j*dx+n) end
            c = concat(c,"",1,nx)
    r[#r+1] = c
  end
  r = concat(r,"\r",1,ny)
  figures.bitmapimage {data=r,xresolution=nx,yresolution=ny}
end
\stopluacode
%StopShownPreambleCommands
\starttext
\defineoverlay[BitMess][{\scale[width=\dimexpr\overlaywidth+2ex,
                                height=\dimexpr\overlayheight+2ex]{\ctxlua{%
  document.TestBitmap(\number\dimexpr\overlaywidth,
                      \number\dimexpr\overlayheight)}}}]
\framed[width=10cm,height=10cm,frame=off,
        background={BitMess,color},backgroundcolor=white]{test}
\stoptext