path: root/metapost/context/base/mp-core.mpiv

%D \module
%D   [       file=mp-core.mp,
%D        version=1999.08.01, % anchoring
%D          title=\CONTEXT\ \METAPOST\ graphics,
%D       subtitle=background macros,
%D         author=Hans Hagen,
%D           date=\currentdate,
%D      copyright={PRAGMA / Hans Hagen \& Ton Otten}]
%C
%C This module is part of the \CONTEXT\ macro||package and is
%C therefore copyrighted by \PRAGMA. See mreadme.pdf for
%C details.

if known context_core : endinput ; fi ;

boolean context_core ; context_core := true ;

pair    lxy[], rxy[], cxy[], llxy[], lrxy[], ulxy[], urxy[] ;
path    pxy[] ;
numeric hxy[], wxy[], dxy[], nxy[] ;

def box_found (expr n,x,y,w,h,d) =
    not ((x=0) and (y=0) and (w=0) and (h=0) and (d=0))
enddef ;

def initialize_box_pos (expr pos,n,x,y,w,h,d) =
    pair lxy, rxy, cxy, llxy, lrxy, ulxy, urxy ;
    path pxy ; numeric hxy, wxy, dxy, nxy;
    lxy  := (x,y) ;
    llxy := (x,y-d) ;
    lrxy := (x+w,y-d) ;
    urxy := (x+w,y+h) ;
    ulxy := (x,y+h) ;
    wxy  := w ;
    hxy  := h ;
    dxy  := d ;
    rxy  := lxy shifted (wxy,0) ;
    pxy  := llxy--lrxy--urxy--ulxy--cycle ;
    cxy  := center pxy ;
    nxy  := n ;
    freeze_box(pos) ;
enddef ;

def freeze_box (expr pos) =
    lxy[pos]  := lxy  ;
    llxy[pos] := llxy ;
    lrxy[pos] := lrxy ;
    urxy[pos] := urxy ;
    ulxy[pos] := ulxy ;
    wxy[pos]  := wxy  ;
    hxy[pos]  := hxy  ;
    dxy[pos]  := dxy  ;
    rxy[pos]  := rxy  ;
    pxy[pos]  := pxy  ;
    cxy[pos]  := cxy  ;
    nxy[pos]  := nxy  ;
enddef ;

def initialize_box (expr n,x,y,w,h,d) =
    numeric bpos ; bpos := 0 ; initialize_box_pos(bpos,n,x,y,w,h,d) ;
enddef ;

def initialize_area (expr fn,fx,fy,fw,fh,fd,
                          tn,tx,ty,tw,th,td) =
    numeric fpos ; fpos := 1 ; initialize_box_pos(fpos,fn,fx,fy,fw,fh,fd) ;
    numeric tpos ; tpos := 2 ; initialize_box_pos(tpos,tn,tx,ty,tw,th,td) ;
    do_initialize_area (fpos, tpos) ;
enddef ;

def do_initialize_area (expr fpos, tpos) =
    lxy  := lxy[fpos] ;
    llxy := (xpart llxy[fpos], ypart llxy[tpos]) ;
    lrxy := lrxy[tpos] ;
    urxy := (xpart urxy[tpos], ypart urxy[fpos]) ;
    ulxy := ulxy[fpos] ;
    wxy  := xpart lrxy - xpart llxy ;
    hxy  := hxy[fpos] ;
    dxy  := dxy[tpos] ;
    rxy  := lxy shifted (wxy,0) ;
    pxy  := llxy--lrxy--urxy--ulxy--cycle ;
    cxy  := center pxy ;
enddef ;

def set_par_line_height (expr ph, pd) =
    par_strut_height := if ph>0 : ph elseif StrutHeight>0 : StrutHeight else : 8pt fi ;
    par_strut_depth  := if pd>0 : pd elseif StrutDepth >0 : StrutDepth  else : 3pt fi ;
    par_line_height  := par_strut_height + par_strut_depth ;
enddef ;

def initialize_par (expr fn,fx,fy,fw,fh,fd,
                         tn,tx,ty,tw,th,td,
                         mn,mx,my,mw,mh,md,
                         pn,px,py,pw,ph,pd,
                         rw,rl,rr,rh,ra,ri) =

    numeric fpos ; fpos := 1 ; initialize_box_pos(fpos,fn,fx,fy,fw,fh,fd) ;
    numeric tpos ; tpos := 2 ; initialize_box_pos(tpos,tn,tx,ty,tw,th,td) ;
    numeric mpos ; mpos := 3 ; initialize_box_pos(mpos,mn,mx,my,mw,mh,md) ;
    numeric ppos ; ppos := 4 ; initialize_box_pos(ppos,pn,px,py,pw,ph,pd) ;

    numeric par_strut_height, par_strut_depth, par_line_height ;

    set_par_line_height (ph, pd) ;

    do_initialize_area (fpos, tpos) ;
    do_initialize_par  (fpos, tpos, mpos, ppos, rw,rl,rr,rh,ra,ri) ;

enddef ;

def initialize_area_par (expr fn,fx,fy,fw,fh,fd,
                              tn,tx,ty,tw,th,td,
                              wn,wx,wy,ww,wh,wd) =

    numeric fpos ; fpos := 1 ; initialize_box_pos(fpos,fn,fx,fy,fw,fh,fd) ;
    numeric tpos ; tpos := 2 ; initialize_box_pos(tpos,tn,tx,ty,tw,th,td) ;
    numeric wpos ; wpos := 3 ; initialize_box_pos(wpos,wn,wx,wy,ww,wh,wd) ;

    numeric par_strut_height, par_strut_depth, par_line_height ;

    set_par_line_height (wh, wd) ;

    numeric ffpos ; ffpos := 4 ; initialize_box_pos(ffpos,wn,wx,fy,0,wh,wd) ;
    numeric ttpos ; ttpos := 5 ; initialize_box_pos(ttpos,wn,wx+ww,ty,0,wh,wd) ;

    do_initialize_area (ffpos, ttpos) ;

    numeric mpos ; mpos := 6 ; freeze_box(mpos) ;

    do_initialize_par  (fpos, tpos, mpos, ffpos, 0,0,0,0,0,0) ;

enddef ;

def do_initialize_par (expr fpos, tpos, mpos, ppos, rw,rl,rr,rh,ra,ri) =

    pair lref, rref, pref, lhref, rhref ;

    % clip the page area to the left and right skips

    llxy[mpos] := llxy[mpos] shifted (+rl,0) ;
    lrxy[mpos] := lrxy[mpos] shifted (-rr,0) ;
    urxy[mpos] := urxy[mpos] shifted (-rr,0) ;
    ulxy[mpos] := ulxy[mpos] shifted (+rl,0) ;

    % fixate the leftskip, rightskip and hanging indentation

    lref := (xpart llxy[mpos],ypart ulxy[ppos]) ; lhref := lref shifted (rh,0) ;
    rref := (xpart lrxy[mpos],ypart urxy[ppos]) ; rhref := rref shifted (rh,0) ;

    pref := lxy[ppos] ;

    if nxy[tpos] > nxy[fpos] :
        if nxy[fpos] = nxy[mpos] :
            % first of multiple pages
            llxy[tpos] := llxy[mpos] ;
            lrxy[tpos] := lrxy[mpos] ;
            urxy[tpos] := lrxy[mpos] shifted (0,par_line_height) ;
            ulxy[tpos] := llxy[mpos] shifted (0,par_line_height) ;
            boxgriddirection := down ;
        elseif nxy[tpos] = nxy[mpos] :
            % last of multiple pages
            llxy[fpos] := ulxy[mpos] shifted (0,-par_line_height) ;
            lrxy[fpos] := urxy[mpos] shifted (0,-par_line_height) ;
            urxy[fpos] := urxy[mpos] ;
            ulxy[fpos] := ulxy[mpos] ;
            boxgriddirection := up ;
        else :
            % middle of multiple pages
            llxy[fpos] := ulxy[mpos] shifted (0,-par_line_height) ;
            lrxy[fpos] := urxy[mpos] shifted (0,-par_line_height) ;
            urxy[fpos] := urxy[mpos] ;
            ulxy[fpos] := ulxy[mpos] ;
            llxy[tpos] := llxy[mpos] ;
            lrxy[tpos] := lrxy[mpos] ;
            urxy[tpos] := lrxy[mpos] shifted (0,par_line_height) ;
            ulxy[tpos] := llxy[mpos] shifted (0,par_line_height) ;
            boxgriddirection := up ;
        fi ;
    else :
        % just one page
        boxgriddirection := up ;
    fi ;

    path txy, bxy, pxy, mxy ;

    txy := originpath ; % top
    bxy := originpath ; % bottom
    pxy := originpath ; % composed

    boolean lefthang, righthang, somehang ;

    % we only hang on the first of a multiple page background

    if nxy[mpos] > nxy[fpos] :
        lefthang := righthang := somehang := false ;
    else :
        lefthang := (rh>0) ; righthang := (rh<0) ; somehang := false ;
    fi ;

    if lefthang :
        mxy  := boundingbox (lref -- lref shifted (rh,ra*par_line_height)) ;
    elseif righthang :
        mxy  := boundingbox (rref -- rref shifted (rh,ra*par_line_height)) ;
    else :
        mxy  := originpath ;
    fi ;

    if round(ypart llxy[fpos]) = round(ypart llxy[tpos]) :

        % We have a one-liner. Watch how er use the bottom pos for
        % determining the height.

        llxy[fpos] := (xpart llxy[fpos], ypart llxy[tpos]) ;
        ulxy[fpos] := (xpart ulxy[fpos], ypart ulxy[tpos]) ;

    else :

        % We have a multi-liner. For convenience we now correct the
        % begin and end points for indentation.

        if lefthang and (round(ypart llxy[tpos]) >= round(ypart lrcorner mxy)) :
            llxy[tpos] := (xpart lhref, ypart llxy[tpos]) ;
            ulxy[tpos] := (xpart lhref, ypart ulxy[tpos]) ;
        else :
            llxy[tpos] := (xpart  lref, ypart llxy[tpos]) ;
            ulxy[tpos] := (xpart  lref, ypart ulxy[tpos]) ;
        fi ;

        if righthang and (round(ypart lrxy[fpos]) >= round(ypart llcorner mxy)) :
            lrxy[fpos] := (xpart rhref, ypart lrxy[fpos]) ;
            urxy[fpos] := (xpart rhref, ypart urxy[fpos]) ;
        else :
            lrxy[fpos] := (xpart  rref, ypart lrxy[fpos]) ;
            urxy[fpos] := (xpart  rref, ypart urxy[fpos]) ;
        fi ;

    fi ;

    somehang := (ypart ulxy[fpos]>ypart llcorner mxy) and
                (ypart llxy[tpos]<ypart llcorner mxy) ;

    if round(ypart llxy[fpos]) = round(ypart llxy[tpos]) :

        % A (short) one-liner goes into the top box.

        txy := llxy[fpos] -- lrxy[tpos] -- urxy[tpos] -- ulxy[fpos] -- cycle ;

    elseif (round(ypart llxy[fpos]) = round(ypart ulxy[tpos])) and
           (round(xpart lrxy[tpos]) < round(xpart llxy[fpos])) :

        % We have a sentence that spans two lines but with only end
        % of line and begin of line segments. We need to take care of
        % indentation.

        txy := llxy[fpos] -- lrxy[fpos] -- urxy[fpos] -- ulxy[fpos] -- cycle ;
        bxy := llxy[tpos] -- lrxy[tpos] -- urxy[tpos] -- ulxy[tpos] -- cycle ;

    elseif (round(ypart llxy[fpos]) = round(ypart ulxy[tpos])) :

        % We have a sentence that spans two lines but with overlap.

        pxy :=
            llxy[tpos] -- lrxy[tpos] -- urxy[tpos] -- lrxy[fpos] --
            urxy[fpos] -- ulxy[fpos] -- llxy[fpos] -- ulxy[tpos] -- cycle ;

    elseif lefthang and somehang :

        % We have a sentence that spans more than two lines with
        % left hanging indentation.

        pxy :=
            llxy[tpos] -- lrxy[tpos] -- urxy[tpos] --
            (xpart urxy[fpos],ypart urxy[tpos]) --
            urxy[fpos] -- ulxy[fpos] -- llxy[fpos] --
            if round(ypart urxy[tpos]) < round(ypart llcorner mxy) :
               (xpart lrcorner mxy,ypart llxy[fpos]) --
               lrcorner mxy --
               (xpart llxy[tpos],ypart llcorner mxy) --
            else :
               (xpart llxy[tpos],ypart llxy[fpos]) --
            fi
            cycle ;

    elseif righthang and somehang :

        % We have a sentence that spans more than two lines with
        % right hanging indentation.

        pxy :=
            llxy[tpos] -- lrxy[tpos] -- urxy[tpos] --
            if round(ypart urxy[tpos]) < round(ypart llcorner mxy) :
                (xpart lrcorner mxy,ypart urxy[tpos]) --
                lrcorner mxy -- llcorner mxy --
            else :
                (xpart urxy[fpos],ypart urxy[tpos]) --
            fi
            urxy[fpos] -- ulxy[fpos] -- llxy[fpos] --
            (xpart llxy[tpos],ypart llxy[fpos]) --
            cycle ;

    else :

        % We have a sentence that spans more than two lines with
        % no hanging indentation.

        pxy :=
            llxy[tpos] -- lrxy[tpos] -- urxy[tpos] --
            (xpart urxy[fpos],ypart urxy[tpos]) --
            urxy[fpos] -- ulxy[fpos] -- llxy[fpos] --
            (xpart llxy[tpos],ypart llxy[fpos]) --
            cycle ;

    fi ;

    pxy := simplified pxy ;
    pxy := unspiked   pxy ;

enddef ;

TopSkip     := 0 ; % will move
StrutHeight := 0 ; % will move

pair last_multi_par_shift ; last_multi_par_shift := origin ;

def relocate_multipars (expr xy) =
    last_multi_par_shift := xy ;
    for i=1 upto nofmultipars :
        multipars[i] := multipars[i] shifted last_multi_par_shift ;
    endfor ;
enddef ;

boolean compensate_multi_par_topskip ;
boolean span_multi_column_pars ;
boolean auto_multi_par_hsize ;
boolean enable_multi_par_fallback ;

compensate_multi_par_topskip := true ;
span_multi_column_pars       := false ;
auto_multi_par_hsize         := false ; % true ;
enable_multi_par_fallback    := true ;

vardef multi_par_at_top (expr i) =
  (round (ypart ulcorner multipars[i]) = round (ypart ulcorner (TextAreas[multirefs[i]] shifted last_multi_par_shift)))
enddef ;

numeric nofmultipars ; nofmultipars := 0 ;

boolean obey_multi_par_hang    ; obey_multi_par_hang    := true  ;
boolean obey_multi_par_more    ; obey_multi_par_more    := true  ;
boolean snap_multi_par_tops    ; snap_multi_par_tops    := true  ;
boolean local_multi_par_area   ; local_multi_par_area   := false ;
boolean ignore_multi_par_page  ; ignore_multi_par_page  := false ;
boolean force_multi_par_chain  ; force_multi_par_chain  := true  ;
boolean one_piece_multi_par    ; one_piece_multi_par    := false ;
boolean check_multi_par_chain  ; check_multi_par_chain  := true  ; % extra page check

boolean multi_column_first_page_hack; multi_column_first_page_hack := true ; % seems to work ok

def simplify_multi_pars = % boundingbox ipv shape als optie
    for i := 1 upto nofmultipars :
        multipars[i] := boundingbox multipars[i] ;
    endfor ;
enddef ;

def save_multipar (expr i, l, p) =
    nofmultipars := nofmultipars + 1 ;
    multirefs[nofmultipars] := i ;
    multilocs[nofmultipars] := l ;
    multipars[nofmultipars] := unspiked (simplified p) ;
enddef ;

def prepare_multi_pars (expr fn,fx,fy,fw,fh,fd,
                             tn,tx,ty,tw,th,td,
                             wn,wx,wy,ww,wh,wd,
                             pn,px,py,pw,ph,pd,
                             rw,rl,rr,rh,ra,ri) =

    if span_multi_column_pars :
        begingroup ;
        save TextAreas ; path TextAreas[] ;
        save NOfTextAreas ; numeric NOfTextAreas ;
        for i=1 upto NOfTextColumns :
            TextAreas[i] := TextColumns[i] ;
        endfor ;
        NOfTextAreas := NOfTextColumns ;
    fi ;

    last_multi_par_shift := origin ;

    numeric fpos ; fpos := 1 ; initialize_box_pos(fpos,fn,fx,fy,fw,fh,fd) ;
    numeric tpos ; tpos := 2 ; initialize_box_pos(tpos,tn,tx,ty,tw,th,td) ;
    numeric wpos ; wpos := 3 ; initialize_box_pos(wpos,wn,wx,wy,ww,wh,wd) ;
    numeric ppos ; ppos := 4 ; initialize_box_pos(ppos,pn,px,py,pw,ph,pd) ;

    if local_multi_par_area :
        RealPageNumber := fn ;
        NOfTextAreas := 1 ;
        NOfSavedTextAreas := 0 ;
        TextAreas[1] := TextAreas[0] ;
        TextColumns[1] := TextColumns[0] ;
        nxy[fpos] := nxy[tpos] := nxy[wpos] := nxy[ppos] := RealPageNumber ;
    elseif ignore_multi_par_page :
        RealPageNumber := fn ;
        nxy[fpos] := nxy[tpos] := nxy[wpos] := nxy[ppos] := RealPageNumber ;
    fi ;

    numeric par_strut_height, par_strut_depth, par_line_height ;

    set_par_line_height (ph, pd) ;

    numeric par_hang_indent, par_hang_after, par_indent, par_left_skip, par_right_skip ;

    par_hang_indent  := rh ;
    par_hang_after   := ra ;
    par_indent       := ri ;
    par_left_skip    := rl ;
    par_right_skip   := rr ;

    pair par_start_pos ;
    pair par_stop_pos ;

    par_start_pos := llxy[fpos]
        if par_indent   <0: shifted (-par_indent,   0) fi
        if par_left_skip<0: shifted (-par_left_skip,0) fi ;

    par_stop_pos := lrxy[tpos]
        if par_right_skip<0: shifted (par_right_skip,0) fi ; % nasty as the endpos can be shifted by rightskip

    if wxy[wpos]>0 :
        left_skip  := rl + xpart llxy[wpos] - xpart llxy[ppos] ;
        right_skip := rw - left_skip - ww ;
    else :
        left_skip  := rl ;
        right_skip := rr ;
    fi ;

    path    multipar, multipars[] ;
    numeric multiref, multirefs[] ;
    numeric multiloc, multilocs[] ; % 1=begin 2=between 3=end

    numeric multi_par_pages ; multi_par_pages := nxy[tpos]-nxy[fpos]+1 ;

    % locals .. why can't i move these outside?

    vardef _pmp_set_multipar_ (expr i) =
        ( (TextAreas[i] leftenlarged -left_skip) rightenlarged (-right_skip
        if auto_multi_par_hsize : + rw - bbwidth(TextAreas[i]) fi) )
    enddef ;

    vardef _pmp_snapped_multi_pos_ (expr p) =
        if snap_multi_par_tops :
            if abs(ypart p - ypart ulcorner multipar) < par_line_height :
                (xpart p,ypart ulcorner multipar)
            else :
                p
            fi
        else :
            p
        fi
    enddef ;

    vardef _pmp_estimated_par_lines_ (expr h) =
        round(h/par_line_height)
    enddef ;

    vardef _pmp_top_multi_par_(expr p) =
        (round(_pmp_estimated_par_lines_(bbheight(p)*par_line_height))=round(bbheight(p)))
    enddef ;

    vardef _pmp_multi_par_tsc_(expr p) =
        if _pmp_top_multi_par_(p) : TopSkipCorrection else : 0 fi
    enddef ;

    vardef _pmp_estimated_multi_par_height_ (expr n, t) =
        if round(par_line_height)=0 :
            0
        else :
            save ok, h ; boolean ok ;
            numeric h ; h := 0 ;
            ok := false ;
            if (nxy[fpos]=RealPageNumber-1) :
                for i := 1 upto NOfSavedTextAreas :
                    if (InsideSavedTextArea(i,par_start_pos)) :
                        ok := true ;
                        h := h + _pmp_estimated_par_lines_(ypart ulxy[fpos] - ypart llcorner SavedTextAreas[i]) ;
                    elseif ok :
                        h := h + _pmp_estimated_par_lines_(bbheight(SavedTextAreas[i])) ;
                    fi ;
                endfor ;
            fi ;
            if ok :
                for i := 1 upto n-1 :
                    h := h + _pmp_estimated_par_lines_(bbheight(TextAreas[i])) ;
                endfor ;
            else :
                % already: ok := false ;
                for i := 1 upto n-1 :
                    if (InsideTextArea(i,par_start_pos)) :
                        ok := true ;
                        h := h + _pmp_estimated_par_lines_(ypart ulxy[fpos] - ypart llcorner TextAreas[i]) ;
                    elseif ok :
                        h := h + _pmp_estimated_par_lines_(bbheight(TextAreas[i])) ;
                    fi ;
                endfor ;
            fi ;
            h
        fi
    enddef ;

    vardef _pmp_left_top_hang_ (expr same_area) =

        par_hang_after := ra + _pmp_estimated_par_lines_(py-fy) ;

        if (par_hang_indent>0) and (par_hang_after<0) and obey_multi_par_hang :
            pair _ul_ ; _ul_ := (xpart ulcorner multipar, ypart _pmp_snapped_multi_pos_(ulxy[fpos]));
            pair _pa_ ; _pa_ := _ul_ shifted (0,par_hang_after*par_line_height) ;
            _pa_ := (xpart _pa_,max(ypart _pa_ -TopSkipCorrection,ypart llcorner multipar)) ;
            if same_area :
                _pa_ := (xpart _pa_,max(ypart _pa_ -TopSkipCorrection,ypart llxy[tpos])) ;
            fi ;
            if obey_multi_par_more and (round(par_line_height)>0) :
                par_hang_after := min(0,round(par_hang_after + (ypart urxy[fpos]-ypart _pa_)/par_line_height)) ;
            fi ;
            (xpart _ul_ + par_hang_indent, ypart lrxy[fpos]) --
            (xpart _ul_ + par_hang_indent, ypart _pa_) --
            (xpart ulcorner multipar, ypart _pa_)
        else :
            (xpart ulcorner multipar, ypart lrxy[fpos])
        fi
    enddef ;

    vardef _pmp_right_top_hang_ (expr same_area) =

        par_hang_after := ra + _pmp_estimated_par_lines_(py-fy) ;

        if (par_hang_indent<0) and (par_hang_after<0) and obey_multi_par_hang :
            pair _ur_ ; _ur_ := (xpart urcorner multipar, ypart _pmp_snapped_multi_pos_(urxy[fpos])) ;
            pair _pa_ ; _pa_ := _ur_ shifted (0,par_hang_after*par_line_height) ;
            _pa_ := (xpart _pa_,max(ypart _pa_ -TopSkipCorrection,ypart llcorner multipar)) ;
            if same_area :
                _pa_ := (xpart _pa_,max(ypart _pa_ -TopSkipCorrection,ypart _pmp_snapped_multi_pos_(ulxy[tpos]))) ;
            fi ;
            if obey_multi_par_more and (round(par_line_height)>0) :
                par_hang_after := min(0,round(par_hang_after + (ypart urxy[fpos]-ypart _pa_)/par_line_height)) ;
            fi ;
            (xpart urcorner multipar, ypart _pa_) --
            (xpart _ur_ + par_hang_indent, ypart _pa_) --
            (xpart _ur_ + par_hang_indent, ypart _pmp_snapped_multi_pos_(urxy[fpos]))
        else :
            (xpart urcorner multipar, ypart _pmp_snapped_multi_pos_(urxy[fpos]))
        fi
    enddef ;

    vardef _pmp_x_left_top_hang_ (expr i, t) =
        par_hang_after := min(0,ra + _pmp_estimated_multi_par_height_(i,t)) ;
        if (par_hang_indent>0) and (par_hang_after<0) :
            pair _ul_ ; _ul_ := ulcorner multipar ;
            pair _pa_ ; _pa_ := _ul_ shifted (0,par_hang_after*par_line_height) ;
            _pa_ := (xpart _pa_,max(ypart _pa_,ypart llcorner multipar)) ;
            if t :
                _pa_ := (xpart _pa_,max(ypart _pa_,ypart llxy[tpos]));
            fi ;
            if abs(ypart _pa_-ypart llxy[tpos])<par_line_height :
                _pa_ := (xpart _pa_,ypart llxy[tpos]);
            fi ;
            if abs(ypart _pa_-ypart llcorner multipar)<par_line_height :
                _pa_ := (xpart _pa_,ypart llcorner multipar);
            fi ;
            (xpart _ul_, ypart _pa_) --
            (xpart _ul_ + par_hang_indent, ypart _pa_) --
            (xpart _ul_ + par_hang_indent, ypart _ul_)
        else :
            ulcorner multipar
        fi
    enddef ;

    vardef _pmp_x_right_top_hang_ (expr i, t) =
        par_hang_after := min(0,ra + _pmp_estimated_multi_par_height_(i,t)) ;
        if (par_hang_indent<0) and (par_hang_after<0) :
            pair _ur_ ; _ur_ := urcorner multipar ;
            pair _pa_ ; _pa_ := _ur_ shifted (0,par_hang_after*par_line_height) ;
            _pa_ := (xpart _pa_,max(ypart _pa_,ypart lrcorner multipar)) ;
            if t :
                _pa_ := (xpart _pa_,max(ypart _pa_,ypart _pmp_snapped_multi_pos_(urxy[tpos]))) ;
            fi ;
            (xpart _ur_ + par_hang_indent, ypart _ur_) --
            (xpart _ur_ + par_hang_indent, ypart _pa_) --
            (xpart _ur_, ypart _pa_)
        else :
            urcorner multipar
        fi
    enddef ;

    vardef _pmp_left_bottom_hang_ (expr same_area) =
        pair _ll_, _sa_, _pa_ ;
        _sa_ := if same_area : llxy[tpos] else : lrcorner multipar fi ;
        if (par_hang_indent>0) and (par_hang_after>0) and obey_multi_par_hang :
            _ll_ := (xpart ulcorner multipar, ypart _pmp_snapped_multi_pos_(ulxy[fpos])) ;
            _pa_ := _ll_ shifted (0,-par_hang_after*par_line_height) ;
            _pa_ := (xpart _pa_,max(ypart _pa_,ypart llcorner multipar)) ;
            if same_area :
                _pa_ := (xpart _pa_,max(ypart _pa_,ypart _sa_)) ;
            fi ;
            if obey_multi_par_more and (round(par_line_height)>0) :
                par_hang_after := max(0,round(par_hang_after - (ypart urxy[fpos]-ypart _pa_)/par_line_height)) ;
            fi ;
            _pa_ --
            (xpart _pa_ + par_hang_indent,ypart _pa_) --
            (xpart _pa_ + par_hang_indent,ypart _sa_)
        else :
            (xpart llcorner multipar, ypart _sa_)
        fi
    enddef ;

    vardef _pmp_right_bottom_hang_ (expr same_area) =
        pair _lr_, _sa_, _pa_ ;
        _sa_ := if same_area : _pmp_snapped_multi_pos_(ulxy[tpos]) else : lrcorner multipar fi ;
        if (par_hang_indent<0) and (par_hang_after>0) and obey_multi_par_hang :
            _lr_ := (xpart urcorner multipar, ypart _pmp_snapped_multi_pos_(urxy[fpos])) ;
            _pa_ := _lr_ shifted (0,-par_hang_after*par_line_height) ;
            _pa_ := (xpart _pa_,max(ypart _pa_,ypart lrcorner multipar)) ;
            if same_area :
                _pa_ := (xpart _pa_,max(ypart _pa_,ypart _pmp_snapped_multi_pos_(ulxy[tpos]))) ;
            fi ;
            if obey_multi_par_more and (round(par_line_height)>0) :
                par_hang_after := max(0,round(par_hang_after - (ypart urxy[fpos]-ypart _pa_)/par_line_height)) ;
            fi ;
            (xpart _pa_ + par_hang_indent,ypart _sa_) --
            (xpart _pa_ + par_hang_indent,ypart _pa_) --
            _pa_
        else :
        (xpart lrcorner multipar, ypart _sa_)
        fi
    enddef ;

    vardef _pmp_x_left_bottom_hang_ (expr i, t) =
        pair _ll_, _sa_, _pa_ ;
        _sa_ := if t : llxy[tpos] else : llcorner multipar fi ;
        if (par_hang_indent>0) and (ra>0) :
            par_hang_after := max(0,ra - _pmp_estimated_multi_par_height_(i,t)) ;
            _ll_ := ulcorner multipar ;
            _pa_ := _ll_ shifted (0,-par_hang_after*par_line_height) ;
            _pa_ := (xpart _pa_,max(ypart _pa_,ypart llcorner multipar)) ;
            _pa_ := (xpart _pa_,max(ypart _pa_,ypart _sa_)) ;
            % we need to compensate for topskip enlarged areas
            if abs(ypart _pa_ - ypart _sa_) > par_line_height :
                (xpart _pa_ + par_hang_indent,ypart _sa_) --
                (xpart _pa_ + par_hang_indent,ypart _pa_) --
            fi
            _pa_
        else :
            (xpart llcorner multipar, ypart _sa_)
        fi
    enddef ;

    vardef _pmp_x_right_bottom_hang_ (expr i, t) =
        pair _lr_, _sa_, _pa_ ;
        _sa_ := if t : _pmp_snapped_multi_pos_(ulxy[tpos]) else : llcorner multipar fi ;
        if (par_hang_indent<0) and (ra>0) :
            par_hang_after := max(0,ra - _pmp_estimated_multi_par_height_(i, t)) ;
            _lr_ := urcorner multipar ;
            _pa_ := _lr_ shifted (0,-par_hang_after*par_line_height) ;
            _pa_ := (xpart _pa_,max(ypart _pa_,ypart lrcorner multipar)) ;
            _pa_ := (xpart _pa_,max(ypart _pa_,ypart _sa_)) ;
            % we need to compensate for topskip enlarged areas
            _pa_
            if abs(ypart _pa_ - ypart _sa_) > par_line_height :
                -- (xpart _pa_ + par_hang_indent,ypart _pa_)
                -- (xpart _pa_ + par_hang_indent,ypart _sa_)
            fi
        else :
            (xpart lrcorner multipar, ypart _sa_)
        fi
    enddef ;

    % def _pmp_test_multipar_ =
    %     multipar := boundingbox multipar ;
    % enddef ;

    % first loop

    ii := 0 ; nn := NOfTextAreas+1 ; nofmultipars := 0 ;

    if enable_multi_par_fallback  and (nxy[fpos]=RealPageNumber)
        and (nxy[tpos]=RealPageNumber) and not (InsideSomeTextArea(lxy[fpos]) and InsideSomeTextArea(rxy[tpos])) :

        % fallback

        % multipar :=
        %     llxy[fpos] --
        %     lrxy[tpos] --
        %     urxy[tpos] --
        %     ulxy[fpos] -- cycle ;
        %
        % save_multipar (1,1,multipar) ;

        % we need to take the boundingbox because there can be
        % more lines and we want a proper rectange

        multipar :=
            ulxy[fpos] --
            urxy[tpos] --
            lrxy[fpos] --
            llxy[tpos] -- cycle ;

        save_multipar (1,1,boundingbox(multipar)) ;

    else :

        % normal

        for i=1 upto NOfTextAreas :

            TopSkipCorrection := 0 ;

            multipar := _pmp_set_multipar_(i) ;

            % watch how we compensate for negative indentation

            if (nxy[fpos]=RealPageNumber) and (InsideTextArea(i,par_start_pos)) :

                % first one in chain

                ii := i ;

                if (nxy[tpos]=RealPageNumber) and (InsideTextArea(i,par_stop_pos)) :

                    % in same area

                    nn := i ;

                    if compensate_multi_par_topskip and (round(LineHeight-ph-pd)=0) :

                        TopSkipCorrection := TopSkip - StrutHeight ;

                        if round(ypart ulxy[fpos] + TopSkipCorrection) = round(ypart ulcorner TextAreas[i]) :
                            ulxy[fpos] := ulxy[fpos] shifted (0,TopSkipCorrection) ;
                            urxy[fpos] := urxy[fpos] shifted (0,TopSkipCorrection) ;
                        else :
                            TopSkipCorrection := 0 ;
                        fi ;

                    fi ;

                    if ypart llxy[fpos] = ypart llxy[tpos] :

                        multipar :=
                            llxy[fpos] --
                            lrxy[tpos] --
                            _pmp_snapped_multi_pos_(urxy[tpos]) --
                            _pmp_snapped_multi_pos_(ulxy[fpos]) --
                            cycle ;

                        save_multipar (i,1,multipar) ;

                    elseif (ypart llxy[fpos] = ypart ulxy[tpos]) and (xpart llxy[tpos] < xpart llxy[fpos]) :

                        % two loners

                        multipar := if obey_multi_par_hang :

                            _pmp_right_bottom_hang_(true) --
                            _pmp_right_top_hang_(true) --
                            _pmp_snapped_multi_pos_(urxy[fpos]) --
                            lrxy[fpos] --

                        else :

                            llxy[fpos] --
                            (xpart urcorner multipar, ypart llxy[fpos]) --
                            (xpart urcorner multipar, ypart ulxy[fpos]) --
                            _pmp_snapped_multi_pos_(ulxy[fpos]) --

                        fi cycle ;

                        save_multipar (i,1,multipar) ;

                        multipar := _pmp_set_multipar_(i) ;

                        multipar := if obey_multi_par_hang :

                            _pmp_left_bottom_hang_(true) --
                            llxy[tpos] --
                            _pmp_snapped_multi_pos_(ulxy[tpos]) --
                            _pmp_left_top_hang_(true) --

                        else :

                            (xpart llcorner multipar, ypart llxy[tpos]) --
                            llxy[tpos] --
                            _pmp_snapped_multi_pos_(ulxy[tpos]) --
                            (xpart llcorner multipar, ypart ulxy[tpos]) --

                        fi cycle ;

                        save_multipar (i,1,multipar) ;

                    else :

                        multipar := if obey_multi_par_hang :

                            _pmp_left_bottom_hang_(true) --
                            llxy[tpos] --
                            _pmp_snapped_multi_pos_(ulxy[tpos]) --
                            _pmp_right_bottom_hang_(true) --
                            _pmp_right_top_hang_(true) --
                            _pmp_snapped_multi_pos_(urxy[fpos]) --
                            lrxy[fpos] --
                            _pmp_left_top_hang_(true) --

                        else :

                            (xpart llcorner multipar, ypart llxy[tpos]) --
                            llxy[tpos] --
                            _pmp_snapped_multi_pos_(ulxy[tpos]) --
                            (xpart lrcorner multipar, ypart ulxy[tpos]) --
                            (xpart urcorner multipar, ypart urxy[fpos]) --
                            _pmp_snapped_multi_pos_(urxy[fpos]) --
                            lrxy[fpos] --
                            (xpart ulcorner multipar, ypart lrxy[fpos]) --

                        fi cycle  ;

                        save_multipar (i,1,multipar) ;

                    fi ;

                else :

                    multipar := if obey_multi_par_hang :

                        _pmp_left_bottom_hang_(false) --
                        _pmp_right_bottom_hang_(false) --
                        _pmp_right_top_hang_(false) --
                        _pmp_snapped_multi_pos_(urxy[fpos]) --
                        lrxy[fpos] --
                        _pmp_left_top_hang_(false) --

                    else :

                        llcorner multipar --
                        lrcorner multipar --
                        (xpart urcorner multipar, ypart urxy[fpos]) --
                        _pmp_snapped_multi_pos_(urxy[fpos]) --
                        lrxy[fpos] --
                        (xpart ulcorner multipar, ypart lrxy[fpos]) --

                    fi cycle ;

                    save_multipar (i,1,multipar) ;

                fi ;

            elseif (nxy[tpos]=RealPageNumber) and (InsideTextArea(i,par_stop_pos)) :

                % last one in chain

                nn := i ;

                if obey_multi_par_hang and obey_multi_par_more :

                    multipar :=
                        _pmp_x_left_top_hang_(i,true) --
                        _pmp_x_right_top_hang_(i,true) --
                        _pmp_x_right_bottom_hang_(i,true) --
                        _pmp_snapped_multi_pos_(ulxy[tpos]) --
                        llxy[tpos] --
                        _pmp_x_left_bottom_hang_(i,true) --
                        cycle ;

                else :

                    multipar :=
                        ulcorner multipar --
                        urcorner multipar --
                        (xpart lrcorner multipar, ypart urxy[tpos]) --
                        _pmp_snapped_multi_pos_(ulxy[tpos]) --
                        llxy[tpos] --
                        (xpart llcorner multipar, ypart llxy[tpos]) --
                        cycle ;

                fi ;

                save_multipar (i,3,multipar) ;

            elseif multi_column_first_page_hack and ((nxy[fpos]=RealPageNumber) and (nxy[tpos]>=RealPageNumber) and (NOfTextColumns>1)) :

                save_multipar (i,2,multipar) ;

            else :
                % handled later
            fi ;

        endfor ;


        % second loop

        if force_multi_par_chain or (ii > 1) :

            for i=ii+1 upto nn-1 :

                % rest of chain / todo : hang

                % hm, the second+ column in column sets now gets lost in a NOfTextColumns

                if (not check_multi_par_chain) or ((nxy[fpos]<RealPageNumber) and (nxy[tpos]>RealPageNumber)) :

                    multipar := _pmp_set_multipar_(i) ;

                    if obey_multi_par_hang and obey_multi_par_more :

                        multipar :=
                            _pmp_x_left_top_hang_(i,false) --
                            _pmp_x_right_top_hang_(i,false) --
                            _pmp_x_right_bottom_hang_(i,false) --
                            _pmp_x_left_bottom_hang_(i,false) --
                            cycle ;

                    fi ;

                    save_multipar(i,2,multipar) ;

                fi ;

            endfor ;

        fi ;

        % end of normal/fallback

    fi ;

    if span_multi_column_pars :
        endgroup ;
    fi ;

    % potential safeguard:

    % for i=1 upto nofmultipars :
    %     if length p <= 4 :
    %         multipars[i] := boundingbox(multipars[i]) ;
    %     fi ;
    % end ;

    % quick hack for gb:

    one_piece_multi_par := (nofmultipars=1) and (pn=tn) ;

enddef ;

def boxgridoptions = withcolor .8red   enddef ;
def boxlineoptions = withcolor .8blue  enddef ;
def boxfilloptions = withcolor .8white enddef ;

numeric boxgridtype      ; boxgridtype      := 0 ;
numeric boxlinetype      ; boxlinetype      := 1 ;
numeric boxfilltype      ; boxfilltype      := 1 ;
numeric boxdashtype      ; boxdashtype      := 0 ;
pair    boxgriddirection ; boxgriddirection := up ;
numeric boxgridwidth     ; boxgridwidth     := 1pt ;
numeric boxlinewidth     ; boxlinewidth     := 1pt ;
numeric boxlineradius    ; boxlineradius    := 0pt ;
numeric boxfilloffset    ; boxfilloffset    := 0pt ;
numeric boxgriddistance  ; boxgriddistance  := .5cm ;
numeric boxgridshift     ; boxgridshift     := 0pt ;

def draw_box =
    draw pxy        boxlineoptions withpen pencircle scaled boxlinewidth ;
    draw lxy -- rxy boxlineoptions withpen pencircle scaled boxgridwidth ;
enddef ;

def draw_par  = % 1 2 3 11 12
    do_draw_par(pxy) ; do_draw_par(txy) ; do_draw_par(bxy) ;
    for i = pxy, txy, bxy :
        if boxgridtype = 1 :
            boxgriddirection := origin ;
            draw baseline_grid (i,boxgriddirection,true ) boxgridoptions ;
        elseif boxgridtype = 2 :
            boxgriddirection := origin ;
            draw baseline_grid (i,boxgriddirection,false) boxgridoptions ;
        elseif boxgridtype = 3 :
            boxgriddirection := origin ;
            draw baseline_grid (i,boxgriddirection,true ) boxgridoptions ;
            draw baseline_grid (i,boxgriddirection,true ) shifted (0,ExHeight) boxgridoptions ;
        elseif boxgridtype = 4 :
            boxgriddirection := origin ;
            draw baseline_grid (i,boxgriddirection,true ) shifted (0,ExHeight/2) boxgridoptions ;
        elseif boxgridtype = 11 :
            draw graphic_grid(i,boxgriddistance,boxgriddistance,boxgriddistance/2,boxgriddistance/2) ;
        elseif boxgridtype = 12 :
            draw graphic_grid(i,boxgriddistance,boxgriddistance,0,0) ;
        fi ;
    endfor ;
enddef ;

def do_show_par (expr p, r, c) =
    if length(p) > 2 :
        for i=0 upto length(p) :
            draw fullcircle scaled r shifted point i of p withpen pencircle scaled .5pt withcolor c ;
        endfor ;
    fi ;
    draw p withpen pencircle scaled .5pt withcolor c ;
enddef ;

def show_par  =
    if length(mxy) > 2 :
        draw mxy dashed evenly withpen pencircle scaled .5pt withcolor .5white ;
    fi ;
    do_show_par(txy, 4pt, .5green) ;
    do_show_par(bxy, 6pt, .5blue ) ;
    do_show_par(pxy, 8pt, .5red  ) ;
    draw pref withpen pencircle scaled 2pt ;
enddef ;

def sort_multi_pars =
    if nofmultipars>1 :
        begingroup ;
        save _p_, _n_ ; path _p_ ; numeric _n_ ;
        for i := 1 upto nofmultipars :
            if multilocs[i] = 3 :
                _p_ := multipars[nofmultipars] ;
                multipars[nofmultipars] := multipars[i] ;
                multipars[i] := _p_ ;
                _n_ := multirefs[nofmultipars] ;
                multirefs[nofmultipars] := multirefs[i] ;
                multirefs[i] := _n_ ;
                _n_ := multilocs[nofmultipars] ;
                multilocs[nofmultipars] := multilocs[i] ;
                multilocs[i] := _n_ ;
            fi ;
        endfor ;
        endgroup ;
    fi ;
enddef ;

def collapse_multi_pars =
    if nofmultipars>1 :
        begingroup ;
        save _nofmultipars_ ; numeric _nofmultipars_ ;
        _nofmultipars_ := 1 ;
        sort_multi_pars ; % block not in order: 1, 3, 2....
        for i:=1 upto nofmultipars-1 :
            if (round(xpart(llcorner multipars[i]-llcorner multipars[i+1]))=0) and
               (round(xpart(lrcorner multipars[i]-lrcorner multipars[i+1]))=0) :
                multilocs[_nofmultipars_] := multilocs[i+1] ;
                multirefs[_nofmultipars_] := multirefs[i+1] ;
                multipars[_nofmultipars_] :=
                    ulcorner multipars[_nofmultipars_] --
                    urcorner multipars[_nofmultipars_] --
                    lrcorner multipars[i+1] --
                    llcorner multipars[i+1] -- cycle ;
            else :
                _nofmultipars_ := _nofmultipars_ + 1 ;
                multipars[_nofmultipars_] := multipars[i+1] ;
                multilocs[_nofmultipars_] := multilocs[i+1] ;
                multirefs[_nofmultipars_] := multirefs[i+1] ;
            fi  ;
        endfor ;
        nofmultipars := _nofmultipars_ ;
        endgroup ;
    fi ;
enddef ;

def draw_multi_pars  =
    for i=1 upto nofmultipars :
        do_draw_par(multipars[i]) ;
        if boxgridtype= 1 :
            draw baseline_grid (multipars[i],if multilocs[i]=1: down else: up fi,true) ;
        elseif boxgridtype= 2 :
            draw baseline_grid (multipars[i],if multilocs[i]=1: down else: up fi,false) ;
        elseif boxgridtype= 3 :
            draw baseline_grid (multipars[i],if multilocs[i]=1: down else: up fi,true) ;
            draw baseline_grid (multipars[i],if multilocs[i]=1: down else: up fi,true) shifted (0,ExHeight) ;
        elseif boxgridtype= 4 :
            draw baseline_grid (multipars[i],if multilocs[i]=1: down else: up fi,true) shifted (0,ExHeight/2) ;
        elseif boxgridtype=11 :
            draw graphic_grid(multipars[i],boxgriddistance,boxgriddistance,boxgriddistance/2,boxgriddistance/2) ;
        elseif boxgridtype=12 :
            draw graphic_grid(multipars[i],boxgriddistance,boxgriddistance,0,0) ;
        fi ;
    endfor ;
enddef ;

def show_multi_pars  =
    for i=1 upto nofmultipars :
        do_show_par(multipars[i], 6pt, .5blue) ;
    endfor ;
enddef ;

vardef do_draw_par (expr p) =
    if (length p>2) and (bbwidth(p)>1) and (bbheight(p)>1) :
        save pp ; path pp ;
        if (boxlineradius>0) and (boxlinetype=2) :
            pp := p cornered boxlineradius ;
        else :
            pp := p ;
        fi ;
        if boxfilltype>0 :
            if boxfilloffset>0 :
                % temporary hack
                begingroup ;
                interim linejoin := mitered ;
                filldraw pp boxfilloptions withpen pencircle scaled (2*boxfilloffset) ;
                endgroup ;
            else :
                fill pp boxfilloptions ;
            fi ;
        fi ;
        if boxlinetype>0 :
            draw pp boxlineoptions withpen pencircle scaled boxlinewidth ;
        fi ;
    fi ;
enddef ;

vardef baseline_grid (expr pxy, pdir, at_baseline) =
    if (par_line_height>0) and (bbheight(pxy)>1) and (bbwidth(pxy)>1) and (boxgridwidth>0) :
        save i, grid, bb ; picture grid ; pair start ; path bb ;
        def _do_ (expr start) =
            % 1 = normal, 2 = with background (i.e. no shine-through)
            if boxdashtype = 2 :
                draw
                    start -- start shifted (bbwidth(pxy),0)
                        withpen pencircle scaled boxgridwidth
                        boxfilloptions ;
            fi ;
            draw start -- start shifted (bbwidth(pxy),0)
                if boxdashtype > 0 :
                    dashed evenly
                fi
                withpen pencircle scaled boxgridwidth
                boxgridoptions ;
        enddef ;
        grid := image ( %fails with inlinespace
            if pdir=up :
                for i = if at_baseline : par_strut_depth else : 0 fi step  par_line_height until max(bbheight(pxy),par_line_height) :
                    _do_ (llcorner pxy shifted (0,+i)) ;
                endfor ;
            else :
                for i = if at_baseline : par_strut_height else : 0 fi step  par_line_height until bbheight(pxy) :
                    _do_ (ulcorner pxy shifted (0,-i)) ;
                endfor ;
            fi ;
        ) ;
        clip grid to pxy ;
        bb := boundingbox grid ;
        grid := grid shifted (0,boxgridshift) ;
        setbounds grid to bb ;
        grid
    else :
        nullpicture
    fi
enddef ;

vardef graphic_grid (expr pxy, dx, dy, x, y) =
    if (bbheight(pxy)>dy) and (bbwidth(pxy)>dx) and (boxgridwidth>0) :
        save grid ; picture grid ;
        grid := image (
            for i = xpart llcorner pxy step dx until xpart lrcorner pxy :
                draw (i,ypart llcorner pxy) -- (i,ypart ulcorner pxy) withpen pencircle scaled boxgridwidth ;
            endfor ;
            for i = ypart llcorner pxy step dy until ypart ulcorner pxy :
                draw (xpart llcorner pxy,i) -- (xpart lrcorner pxy,i) withpen pencircle scaled boxgridwidth ;
            endfor
        ) shifted (x,y) ;
        clip grid to pxy ;
        grid
    else :
        nullpicture
    fi
enddef ;

def anchor_box (expr n,x,y,w,h,d) =
    currentpicture := currentpicture shifted (-x,-y) ;
enddef ;

let draw_area   = draw_box ;
let anchor_area = anchor_box ;
let anchor_par  = anchor_box ;

numeric sync_n[], sync_p[][], sync_w[][], sync_h[][], sync_d[][], sync_t[][] ;
pair sync_xy[][] ; color sync_c[][] ;

def ResetSyncTasks =
    path SyncPaths[] ; numeric SyncTasks[], NOfSyncPaths, CurrentSyncClass ;
    NOfSyncPaths := CurrentSyncClass := 0 ;
    if unknown SyncLeftOffset : numeric SyncLeftOffset ; SyncLeftOffset := 0          ; fi ;
    if unknown SyncWidth      : numeric SyncWidth      ; SyncWidth      := 0          ; fi ;
    if unknown SyncThreshold  : numeric SyncThreshold  ; SyncThreshold  := LineHeight ; fi ;
    if unknown SyncColor      : color   SyncColor      ; SyncColor      := .5white    ; fi ;
    if (SyncLeftOffset = 0) and (SyncWidth = 0) :
        SyncWidth := if known TextWidth : TextWidth else : -1cm fi ;
    fi ;
enddef ;

ResetSyncTasks ;

vardef SyncBox(expr n, i, leftoffset, width, topoffset, bottomoffset) =
    save o ; pair o ; o := (xpart llcorner PlainTextArea,ypart sync_xy[n][i]) ;
    o shifted (leftoffset,sync_h[n][i]+topoffset) --
    o shifted (width+leftoffset,sync_h[n][i]+topoffset) --
    o shifted (width+leftoffset,bottomoffset) --
    o shifted (leftoffset,bottomoffset) -- cycle
enddef ;

def SetSyncColor(expr n, i, c) =
    sync_c[n][i] := c ;
enddef ;

def SetSyncThreshold(expr n, i, th) =
    sync_th[n][i] := th ;
enddef ;

vardef TheSyncColor(expr n, i) =
    if known sync_c[n][i] : sync_c[n][i] else : SyncColor fi
enddef ;

vardef TheSyncThreshold(expr n, i) =
    if known sync_th[n][i] : sync_th[n][i] else : SyncThreshold fi
enddef ;

vardef PrepareSyncTasks(expr n, collapse, extendtop, prestartnext) =
    ResetSyncTasks ;
    if known sync_n[n] :
        CurrentSyncClass := n ;
        save ok, l, d ; boolean ok ; ok := false ; NOfSyncPaths := l := 0 ;
        for i=1 upto sync_n[n] :
            if RealPageNumber > sync_p[n][i] :
                l := i ;
            elseif RealPageNumber = sync_p[n][i] :
                NOfSyncPaths := NOfSyncPaths + 1 ;
                if not ok :
                    if i>1 :
                        if sync_t[n][i-1] = sync_t[n][i] :
                            SyncPaths[NOfSyncPaths] := SyncBox(n, i, SyncLeftOffset, SyncWidth, PaperHeight, -PaperHeight) ;
                            SyncTasks[NOfSyncPaths] := i ;
                        else :
                            SyncPaths[NOfSyncPaths] := SyncBox(n, i-1, SyncLeftOffset, SyncWidth, PaperHeight, -PaperHeight) ;
                            SyncTasks[NOfSyncPaths] := i-1 ;
                            NOfSyncPaths := NOfSyncPaths + 1 ;
                            SyncPaths[NOfSyncPaths] := SyncBox(n, i, SyncLeftOffset, SyncWidth, 0, -PaperHeight) ;
                            SyncTasks[NOfSyncPaths] := i ;
                        fi ;
                    else :
                        SyncPaths[NOfSyncPaths] := SyncBox(n, i, SyncLeftOffset, SyncWidth, 0, -PaperHeight) ;
                        SyncTasks[NOfSyncPaths] := i ;
                    fi ;
                else :
                    SyncPaths[NOfSyncPaths] := SyncBox(n, i, SyncLeftOffset, SyncWidth, 0, -PaperHeight) ;
                    SyncTasks[NOfSyncPaths] := i ;
                fi ;
                ok := true ;
            fi ;
        endfor ;
        if (NOfSyncPaths = 0) and (l > 0) :
            NOfSyncPaths := 1 ;
            SyncPaths[NOfSyncPaths] := SyncBox(n, l, SyncLeftOffset, SyncWidth, PaperHeight, -PaperHeight) ;
            SyncTasks[NOfSyncPaths] := l ;
        fi ;
        if NOfSyncPaths > 0 :
            for i = 1 upto NOfSyncPaths-1 :
                SyncPaths[i] := topboundary SyncPaths[i] -- reverse topboundary SyncPaths[i+1] -- cycle ;
            endfor ;
            if unknown SyncThresholdMethod :
                numeric SyncThresholdMethod ; SyncThresholdMethod := 2 ;
            fi ;
            if extendtop :
                if SyncThresholdMethod = 1 :
                    if NOfSyncPaths>1 :
                        d := ypart (ulcorner PlainTextArea - sync_xy[n][SyncTasks[2]]) ;
                        if (SyncTasks[2]>1) and (d > 0pt) and (d <= TheSyncThreshold(n,sync_t[n][SyncTasks[2]])) and (sync_p[n][SyncTasks[2]] = RealPageNumber) :
                            SyncPaths[2] := SyncPaths[2] topenlarged PaperHeight ;
                        fi ;
                    fi ;
                else :
                    for i = 1 upto NOfSyncPaths :
                        d := ypart (ulcorner PlainTextArea - sync_xy[n][SyncTasks[i]]) ;
                        if (d > 0) and (d <= TheSyncThreshold(n,sync_t[n][SyncTasks[i]])) and (sync_p[n][SyncTasks[i]] = RealPageNumber) :
                            SyncPaths[i] := SyncPaths[i] topenlarged PaperHeight ;
                        fi ;
                    endfor ;
                fi ;
            fi ;
            if prestartnext :
                if NOfSyncPaths>1 :
                    if SyncTasks[NOfSyncPaths] < sync_n[n] : % there is a next one
                        d := ypart (ulcorner PlainTextArea - sync_xy[n][SyncTasks[NOfSyncPaths]+1]) ;
                        if (d > 0) and (d <= TheSyncThreshold(n, sync_t[n][SyncTasks[i]])) and (sync_p[n][SyncTasks[NOfSyncPaths]+1] = RealPageNumber+1) :
                            SyncPaths[NOfSyncPaths+1] :=
                                (xpart ulcorner SyncPaths[NOfSyncPaths],ypart llcorner PlainTextArea) --
                                (xpart urcorner SyncPaths[NOfSyncPaths],ypart llcorner PlainTextArea) --
                                lrcorner SyncPaths[NOfSyncPaths] --
                                llcorner SyncPaths[NOfSyncPaths] -- cycle ;
                            SyncTasks[NOfSyncPaths+1] := SyncTasks[NOfSyncPaths]+1 ;
                            NOfSyncPaths := NOfSyncPaths + 1 ;
                        fi ;
                    fi ;
                fi ;
            else :
                if NOfSyncPaths>1 :
                    d := ypart (sync_xy[n][SyncTasks[NOfSyncPaths]] - llcorner PlainTextArea) ;
                    if (d < TheSyncThreshold(n, SyncTasks[NOfSyncPaths])) :
                        NOfSyncPaths := NOfSyncPaths - 1 ;
                        SyncPaths[NOfSyncPaths] := SyncPaths[NOfSyncPaths] bottomenlarged PaperHeight ;
                    fi ;
                fi ;
            fi ;
            if (NOfSyncPaths>1) and collapse :
                save j ; numeric j ; j := 1 ;
                for i = 2 upto NOfSyncPaths :
                    if sync_t[n][SyncTasks[i]] = sync_t[n][SyncTasks[j]] :
                        SyncPaths[j] := boundingbox image (draw SyncPaths[i] ; draw SyncPaths[j] ; ) ;
                        SyncTasks[j] := SyncTasks[i] ;
                    else :
                        j := j + 1 ;
                        SyncPaths[j] := SyncPaths[i] ;
                        SyncTasks[j] := SyncTasks[i] ;
                    fi ;
                endfor ;
                NOfSyncPaths := j ;
            fi ;
        fi ;
    fi ;
enddef ;

def SyncTask(expr n) =
    if known SyncTasks[n] : SyncTasks[n] else : 0 fi
enddef ;

def FlushSyncTasks =
    for i = 1 upto NOfSyncPaths :
        ProcessSyncTask(SyncPaths[i], TheSyncColor(CurrentSyncClass,sync_t[CurrentSyncClass][SyncTasks[i]])) ;
    endfor ;
enddef ;

def ProcessSyncTask(expr p, c) =
    fill p withcolor c ;
enddef ;