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%% This is part of the OpTeX project, see http://petr.olsak.net/optex
\_codedecl \begmulti {Balanced columns <2020-03-26>} % preloaded in format
\_doc -----------------------------
This code is documented in detail in the \"\TeX/book naruby", pages 244--246,
free available, \url{http://petr.olsak.net/tbn.html}, but in Czech.
Roughly speaking, macros complete all material between
\`\begmulti``<num-columns>` and \`\endmulti`
into one `\vbox 6`. Then the macro measures the amount of free space at the current
page using `\pagegoal` and `\pagtotal` and does `\vsplit` of `\vbox 6` to
columns with a height of such free space. This is done only if we have
enough amount of material in `\vbox 6` to fill the full page by columns.
This is repeated in a loop until we have less amount of material in `\vbox 6`.
Then we run `\_balancecolumns` which balances the last part of the columns.
Each part of printed material is distributed to the main vertical list as
`\hbox{<columns>}` and we need not do any change in the output routine.
If you have paragraphs in `\begmulti`... `\endmulti` environment then
you may say `\raggedright` inside this environment and you can re-assign
`\widowpenalty` and `\clubppenalty` (they are set to 10000 in \OpTeX/).
\_cod -----------------------------
\_def\_multiskip{\_medskip} % space above and below \begmulti...\endmulti
\_newcount\_mullines
\_def\_begmulti #1 {\_par\_bgroup\_wipeepar\_multiskip\_penalty0 \_def\_Ncols{#1}
\_setbox6=\_vbox\_bgroup \_let\_setxhsize=\_relax \_penalty0
%% \hsize := column width = (\hsize+\colsep) / n - \colsep
\_advance\_hsize by\_colsep
\_divide\_hsize by\_Ncols \_advance\_hsize by-\_colsep
\_mullines=0
\_def\par{\_ifhmode\_endgraf\_global\_advance\_mullines by\_prevgraf\_fi}%
}
\_def\_endmulti{\_vskip-\_prevdepth\_vfil
\_ea\_egroup\_ea\_baselineskip\_the\_baselineskip\_relax
\_dimen0=.8\_maxdimen \_tmpnum=\_dimen0 \_divide\_tmpnum by\_baselineskip
\_splittopskip=\_baselineskip
\_setbox1=\_vsplit6 to0pt
%% \dimen1 := the free space on the page
\_ifdim\_pagegoal=\_maxdimen \_dimen1=\_vsize \_corrsize{\_dimen1}
\_else \_dimen1=\_pagegoal \_advance\_dimen1 by-\_pagetotal \_fi
\_ifdim \_dimen1<2\_baselineskip
\_vfil\_break \_dimen1=\_vsize \_corrsize{\_dimen1} \_fi
\_ifnum\_mullines<\_tmpnum \_dimen0=\_ht6 \_else \_dimen0=.8\_maxdimen \_fi
\_divide\_dimen0 by\_Ncols \_relax
%% split the material to more pages?
\_ifdim \_dimen0>\_dimen1 \_splitpart
\_else \_balancecolumns \_fi % only balancing
\_multiskip\_egroup
}
\_doc -----------------------------
Splitting columns...
\_cod -----------------------------
\_def\_makecolumns{\_bgroup % full page, destination height: \dimen1
\_vbadness=20000 \_setbox1=\_hbox{}\_tmpnum=0
\_loop \_ifnum\_Ncols>\_tmpnum
\_advance\_tmpnum by1
\_setbox1=\_hbox{\_unhbox1 \_vsplit6 to\_dimen1 \_hss}
\_repeat
\_hbox{}\_nobreak\_vskip-\_splittopskip \_nointerlineskip
\_line{\_unhbox1\_unskip}
\_dimen0=\_dimen1 \_divide\_dimen0 by\_baselineskip \_multiply\_dimen0 by\_Ncols
\_global\_advance\_mullines by-\_dimen0
\_egroup
}
\_def\_splitpart{%
\_makecolumns % full page
\_vskip 0pt plus 1fil minus\_baselineskip \_break
\_ifnum\_mullines<\_tmpnum \_dimen0=\_ht6 \_else \_dimen0=.8\_maxdimen \_fi
\_divide\_dimen0 by\_Ncols \_relax
\_ifx\_balancecolumns\_flushcolumns \_advance\_dimen0 by-.5\_vsize \_fi
\_dimen1=\_vsize \_corrsize{\_dimen1}\_dimen2=\_dimen1
\_advance\_dimen2 by-\_baselineskip
%% split the material to more pages?
\_ifvoid6 \_else
\_ifdim \_dimen0>\_dimen2 \_ea\_ea\_ea \_splitpart
\_else \_balancecolumns % last balancing
\_fi \_fi
}
\_doc -----------------------------
Final balancing of the columns.
\_cod -----------------------------
\_def\_balancecolumns{\_bgroup \_setbox7=\_copy6 % destination height: \dimen0
\_ifdim\_dimen0>\_baselineskip \_else \_dimen0=\_baselineskip \_fi
\_vbadness=20000
\_def\_tmp{%
\_setbox1=\_hbox{}\_tmpnum=0
\_loop \_ifnum\_Ncols>\_tmpnum
\_advance\_tmpnum by1
\_setbox1=\_hbox{\_unhbox1
\_ifvoid6 \_hbox to\_wd6{\_hss}\_else \_vsplit6 to\_dimen0 \_fi\_hss}
\_repeat
\_ifvoid6 \_else
\_advance \_dimen0 by.2\_baselineskip
\_setbox6=\_copy7
\_ea \_tmp \_fi}\_tmp
\_hbox{}\_nobreak\_vskip-\_splittopskip \_nointerlineskip
\_hbox to\_hsize{\_unhbox1\_unskip}%
\_egroup
}
\_def\_corrsize #1{%% #1 := #1 + \splittopskip - \topskip
\_advance #1 by \_splittopskip \_advance #1 by-\_topskip
}
\_public \begmulti \endmulti ;
\_endcode % -------------------------------------
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