%D \module
%D   [       file=mp-blob.mpiv,
%D        version=2018.04.08,
%D          title=\CONTEXT\ \METAPOST\ graphics,
%D       subtitle=Blobs,
%D         author=Hans Hagen,
%D           date=\currentdate,
%D      copyright={PRAGMA ADE \& \CONTEXT\ Development Team}]
%C
%C This module is part of the \CONTEXT\ macro||package and is
%C therefore copyrighted by \PRAGMA. See mreadme.pdf for
%C details.

%D This is a follow up on good old \type {meta-imp-txt}.

if known metafun_loaded_blob : endinput ; fi ;

newinternal boolean metafun_loaded_blob ; metafun_loaded_blob := true ; immutable metafun_loaded_blob ;

numeric mfun_blob_n ; mfun_blob_n := 0 ;
picture mfun_blob_c ;
color   mfun_blob_b ;

def mfun_reset_tex_blobs =
    mfun_blob_n := 0 ;
    mfun_blob_c := nullpicture ;
enddef ;

extra_endfig := extra_endfig & "mfun_reset_tex_blobs ; " ;

vardef mfun_inject_blob(expr n) =
    mfun_blob_c := nullpicture ;
    mfun_blob_b := lua.mp.mf_blob_dimensions(mfun_blob_n,n) ;
    addto mfun_blob_c doublepath unitsquare
        xscaled redpart mfun_blob_b
        yscaled (greenpart mfun_blob_b + bluepart mfun_blob_b)
        shifted (0,- bluepart mfun_blob_b)
        withprescript "mf_object=texblob"
        withprescript "tb_blob=" & decimal lua.mp.mf_blob_index(mfun_blob_n,n) ;
    mfun_blob_c
enddef ;

% An example of usage:

newinternal followtextalternative   ; followtextalternative   := 1 ;
newinternal tracingfollowtext       ; tracingfollowtext       := 0 ;
newinternal autoscaleupfollowtext   ; autoscaleupfollowtext   := 2 ;
newinternal autoscaledownfollowtext ; autoscaledownfollowtext := 0 ;

permanent tracingfollowtext ;

vardef followtext(expr pth, txt) =
    image (
        mfun_blob_n := mfun_blob_n + 1 ;
        lua.mp.mf_inject_blob(mfun_blob_n,txt);
        save pat, al, at, pl, pc, wid, pos, ap, ad, pic, len, n, b, sc, sb ;
        path pat, b ; pat := pth ;
        numeric al, at, pl, pc, wid, pos, len[], n, sc, sb ;
        pair ap, ad ;
        picture pic[] ;
        len[0] := 0 ;
        n := lua.mp.mf_blob_size(mfun_blob_n) ;
        sc := 0 ;
        sb := .25pt;
        for i=1 upto n :
            pic[i] := mfun_inject_blob(i) ;
            pic[i] := pic[i] shifted - llcorner pic[i] ;
            len[i] := len[i-1] + lua.mp.mf_blob_width(mfun_blob_n,i) ;
        endfor ;
        al := arclength pth ;
        if al = 0 :
            al := len[n] ;
            pat := origin -- (al,0) ;
        fi ;
        if ((al < len[n]) and (autoscaleupfollowtext   > 0)) or
           ((al > len[n]) and (autoscaledownfollowtext > 0)) :
            sc := len[n] /al ;
            pat := pat scaled sc ;
            al := arclength pat ;
        fi ;
        if followtextalternative = 1 :
            pl := (al-len[n])/(if n>1 : (n-1) else : 1 fi) ;
            pc := 0 ;
        else : % centered / MP
            pl := 0 ;
            pc := arclength pat/2 - len[n]/2 ;
        fi ;
        if tracingfollowtext = 1 :
            draw pat withpen pencircle scaled 1pt withcolor blue ;
        fi ;
        for i=1 upto n :
            wid := lua.mp.mf_blob_width(mfun_blob_n,i) ;
            pos := len[i]-wid/2 + (i-1)*pl + pc ;
            at := arctime   pos of pat ;
            ap := point     at  of pat ;
            ad := direction at  of pat ;
            pic[i] := pic[i]
                shifted (-wid/2,0)
                if ad <> origin : rotated(angle(ad)) fi
                shifted ap ;
            draw pic[i] ;
            if tracingfollowtext = 1 :
                draw boundingbox pic[i] withpen pencircle scaled .25pt withcolor red ;
                draw ap withpen pencircle scaled .50pt withcolor green ;
            fi ;
        endfor ;
        if ((autoscaleupfollowtext = 2) or (autoscaledownfollowtext = 2)) and (sc <> 0) and (sc <> 1):
            currentpicture := currentpicture scaled (1/sc) ;
            sb := 2 * sb / sc ;
        fi ;
        b := boundingbox currentpicture ;
        if tracingfollowtext = 1 :
            draw b withpen pencircle scaled sb withcolor blue ;
        fi ;
        draw fullcircle scaled 100bp
            withprescript "mf_object=followtext"
            withprescript "ft_category=" & decimal mfun_blob_n ;
        setbounds currentpicture to b ;
    )
enddef ;
