Re: [NTG-context] MetaFun - "remove the paths of text" from a rectangle to let the background visible

23 Dec 2020

      Thanks Taco,

I made some progress :
https://wiki.contextgarden.net/Talk:Cover_Pages

I now have two additional questions ... ;-)

- How can I deal with "space" characters (because current solution
   requires to explicitly add the ~ character)

- What would be the work to do in order to make this mechanism directly
   usable in metapost / metafun, within \startMPpage \stopMPpage,
   - to avoid switching between \start\stopMPdrawing and TeX
   - to have something like "draw followtext" in mp-blob.mpiv ?

%------------------------------------------------------------------------------

\setuppapersize  [A4]

%------------------------------------------------------------------------------

\def\MyFont{\definedfont[name:%
texgyrepagellabold%
%exo2black%
%agaramondprobold%
*default at 55pt]}

%------------------------------------------------------------------------------

\startluacode

function document.outlinepaths(character)
     local chardata  = fonts.hashes.characters[true] -- by unicode
     local shapedata = fonts.hashes.shapes[true] -- by index
     local c         = chardata[character]
     if c and c.index and shapedata then
         local shapeglyphs = shapedata.glyphs or { }
         local glyph       = shapeglyphs[c.index]
         if glyph and (glyph.segments or glyph.sequence) then
             local units  = shapedata.units or 1000
             local factor = 100/units
             return fonts.metapost.paths(glyph,factor)
         end
     end
     return { }
end

function document.defineoutline(char,target)
     local outlines = document.outlinepaths(char)
     local nofpaths = #outlines
     context("\\startMPdrawing")                             -- ADDED by 
garulfo
     context("path %s[] ;",target)
     context("numeric %sn ; %sn := %s ;",target,target,nofpaths)
     for i=1,nofpaths do
         context("%s[%i] := %s ; ",target,i,outlines[i])
     end
     context("\\stopMPdrawing")                              -- ADDED by 
garulfo
end

\stopluacode

%------------------------------------------------------------------------------

\def\mpdefineoutlines#1#2{\ctxlua{document.defineoutline(\number`#1,"#2")}}

%------------------------------------------------------------------------------

\def\EmptyLetters#1%
{%
\resetMPdrawing
\MPtoks={}
%
\startMPdrawing
   picture pic[], pictA ;
   numeric wid[], len[], pos[], n ;
   wid[0] := len[0] := pos[0] := n := 0 ;
   numeric scaling;
   path pictB , frame ;
   pair shiftB ;
   picture monImageA; monImageA := nullpicture;
   picture monImageB; monImageB := nullpicture;
   color colorframe;  colorframe := 0.6white;
%
\stopMPdrawing
%
\MyFont\handletokens#1\with\whatever
%
\startMPdrawing
   frame :=  unitsquare
           xscaled ( (xpart urcorner monImageB - xpart llcorner 
monImageB) + 5mm )
           yscaled ( (ypart urcorner monImageB - ypart llcorner 
monImageB) + 5mm );
   frame := frame shifted (center monImageB - center frame);
   addto monImageB contour
         frame
         withpostscript "evenodd"
         withcolor transparent (1,1.,colorframe);
   draw monImageB ;
   draw monImageA ;
\stopMPdrawing
%
\MPdrawingdonetrue
\getMPdrawing}

%------------------------------------------------------------------------------

\def\whatever#1%
   {\appendtoks#1\to\MPtoks
    \setbox\MPbox=\hbox{\MyFont\the\MPtoks}%
    %
    \startMPdrawing
      n := n + 1 ; len[n] := \the\wd\MPbox ;
    \stopMPdrawing
    %
    \mpdefineoutlines{M}{MaLettre}
    %
    \startMPdrawing
    pictA := textext.drt("\MyFont M") ;
    pictB := MaLettre[1];
    scaling := bbheight pictA / bbheight pictB;
    \stopMPdrawing
    %
    \doifinstringelse{~}{#1}{}{%                HOW TO PROPERLY COPE 
WITH SPACES ?
    \mpdefineoutlines{#1}{MyGlyph}
    %
    \startMPdrawing
      string sb; sb := "i";
      pic[n] := textext.drt("\MyFont\setstrut\strut#1") ;
      %
      shiftB := - llcorner pic[n];
      pic[n] := pic[n] shifted shiftB ;
      %
      wid[n] := abs(xpart urcorner pic[n] - xpart llcorner pic[n]) ;
      pos[n] := len[n]-wid[n] ;
      %
      addto monImageB contour
            ((MyGlyph[1] scaled scaling)
            shifted ( (pos[n],0) +  shiftB))
            withpostscript "collect";
      %
      if MyGlyphn > 1 :
         for ind=2 upto MyGlyphn :
             if (((xpart llcorner MyGlyph[ind]) > (xpart llcorner 
MyGlyph[1])) and
                 ((ypart llcorner MyGlyph[ind]) > (ypart llcorner 
MyGlyph[1])) and
                 ((xpart urcorner MyGlyph[ind]) < (xpart urcorner 
MyGlyph[1])) and
                 ((ypart urcorner MyGlyph[ind]) < (ypart urcorner 
MyGlyph[1]))) :
                 %
                 addto monImageA contour
                       (MyGlyph[ind] scaled scaling)
                       shifted ( (pos[n],0) +  shiftB)
                       withcolor transparent (1,1.,colorframe);
             else :
                 addto monImageB contour
                       (MyGlyph[ind] scaled scaling)
                       shifted ( (pos[n],0) +  shiftB)
                       withpostscript "collect";
             fi;
          endfor;
       fi;
    \stopMPdrawing}}

%==============================================================================
%==============================================================================

\starttext

%------------------------------------------------------------------------------

\startuseMPgraphic{MyBackgroundGraphic}
   path pathbackground ;
   numeric dimA ; dimA := \the\paperwidth;
   numeric dimB ; dimB := \the\paperheight;
   pathbackground :=  unitsquare xscaled dimA yscaled dimB ;
   fill pathbackground
        withshademethod "linear"
        withshadedirection(0,1)
        withshadecolors (red,blue);
\stopuseMPgraphic

%------------------------------------------------------------------------------

\definelayer[MyBackgroundLayer]
\setlayer[MyBackgroundLayer]{\useMPgraphic{MyBackgroundGraphic}}
\setupbackgrounds[page][background={MyBackgroundLayer}]

%------------------------------------------------------------------------------

\EmptyLetters{MetaPost~is~fun!}
\EmptyLetters{ABCDEFGHIJ}
\EmptyLetters{KLMNOPQRST}
\EmptyLetters{UVWXYZ!?\&*}
\EmptyLetters{abcdefghij}
\EmptyLetters{klmnopqrst}
\EmptyLetters{uvwxyz<>;:@}
\EmptyLetters{0123456789}

%------------------------------------------------------------------------------

\stoptext

Le 21/12/2020 à 16:29, Taco Hoekwater a écrit :
...
...
On 21 Dec 2020, at 16:09, Garulfo  wrote:
Hi,
* I try to "remove the paths of text" from a metapost pictures to let
  the background visible.
* Using
  https://mailman.ntg.nl/pipermail/ntg-context/2018/thread.html#92725
* I was able to get the following with one glyph (MVE code below)
https://wiki.contextgarden.net/images/d/d2/test_extract_glyphs.pdf
2 questions:
1/ for some fonts (e.g. dejavu vs latin modern) the "encompassing" path
   of the B glyph can switch from B[1] to B[Bn]. Is there a trick to
   identify which id match with "the encompassing" path ?
What you get is the order of the paths as defined in the font, which is arbitrary, as you discovered.
A quick trick (that will not always work, but should work quite well for font variations of alphabetics) is to check the actual arclength of the paths. The longest one will typically be the outer one.
But much depends on the font, so a generic solution is likely quite complicated. Consider an outline font’s colon glyph ;)
...
2/ now, I would like to do the same, but for text... a kind of
   derivative of "textext" or "outlinetext".
   Would you please give me some guidelines ?
  does it already exist ?
  should I use something like \handletokens, \scantokens ?
  do you have examples where I can get inspiration ?
Thanks again for your help,
Garulfo
%==============================================================================
\starttext
%------------------------------------------------------------------------------
\startluacode
function document.outlinepaths(character)
    local chardata  = fonts.hashes.characters[true] -- by unicode
    local shapedata = fonts.hashes.shapes[true] -- by index
    local c         = chardata[character]
    if c and c.index and shapedata then
        local shapeglyphs = shapedata.glyphs or { }
        local glyph       = shapeglyphs[c.index]
        if glyph and (glyph.segments or glyph.sequence) then
            local units  = shapedata.units or 1000
            local factor = 100/units
            return fonts.metapost.paths(glyph,factor)
        end
    end
    return { }
end
function document.defineoutline(char,target)
    local outlines = document.outlinepaths(char)
    local nofpaths = #outlines
    context("path %s[] ;",target)
    context("numeric %sn ; %sn := %s ;",target,target,nofpaths)
    for i=1,nofpaths do
        context("%s[%i] := %s ; ",target,i,outlines[i])
    end
end
\stopluacode
%------------------------------------------------------------------------------
\def\mpdefineoutlines#1#2{\ctxlua{document.defineoutline(\number`#1,"#2")}}
%------------------------------------------------------------------------------
\startMPpage
numeric dimA ; dimA := 20cm;
path pathbackground ;
pathbackground :=  unitsquare scaled dimA ;
fill pathbackground withshademethod "linear" withshadedirection(0,1) withshadecolors (red,blue);
%--------------------------------------
\mpdefineoutlines{B}{B}
%--------------------------------------
numeric dimB  ; dimB := 2cm;
numeric vratio ; vratio := 2;
path frame ;
frame :=  unitsquare
          xscaled (dimA - 2 * dimB)
          yscaled (dimA / vratio)
          shifted (dimB , (dimA - (dimA / vratio))/2 );
%--------------------------------------
pair shift ; shift := center frame;
numeric scal ; scal := (0.9) * (10cm / (bbheight B[1])) ;
picture monImageB; monImageB := nullpicture;
addto monImageB contour
      (B[1] shifted (- center B[1]) scaled scal)
      shifted shift
      withpostscript "collect";
addto monImageB contour
      frame
      withpostscript "evenodd";
for i=2 upto Bn :
  addto monImageB contour
        (B[i] shifted (- center B[1]) scaled scal)
        shifted shift;
endfor ;
%--------------------------------------
draw monImageB withcolor white;
\stopMPpage
\stoptext
___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!
maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : http://www.pragma-ade.nl / http://context.aanhet.net
archive  : https://bitbucket.org/phg/context-mirror/commits/
wiki     : http://contextgarden.net
___________________________________________________________________________________
Taco Hoekwater
Elvenkind BV
___________________________________________________________________________________
If your question is of interest to others as well, please add an entry to the Wiki!
maillist : ntg-context@ntg.nl / http://www.ntg.nl/mailman/listinfo/ntg-context
webpage  : http://www.pragma-ade.nl / http://context.aanhet.net
archive  : https://bitbucket.org/phg/context-mirror/commits/
wiki     : http://contextgarden.net
___________________________________________________________________________________