\vtop 后的间距

Question

MWE 中的线条间距不足，使用\hbox两个框填充\vtop。

\parindent=0pt

\newdimen\linewidth
\linewidth=4in

\newdimen\colsep
\colsep=1em

\newdimen\colwidth
\colwidth=0.5\linewidth
\advance\colwidth by -1\colsep

\def\twocols#1#2{%                                                                                                                          
    \hbox to \linewidth{%                                                                                                                   
      \vtop{\hsize=\colwidth
        \hangindent=1em \hangafter=1 #1\par}\hfill
      \vtop{\hsize=\colwidth
        \hangindent=1em \hangafter=1 #2\par}\hss
    }\par
}

\twocols
  {This is a very long line that will run over}
  {What is wrong with the spacing?}
\twocols
  {What is wrong with the spacing?}
  {This is a very long line that will run over}

\bye

Answer 1

如果你打开日志记录，你会看到可怕的

..\glue(\lineskip) 1.0

vtop 框具有较大的深度，并且下一个 vtop 试图保持\baselineskip与前一个框的参考点（即第一行的基线）的间距。由于无法实现这一点，TeX 放弃了基线间距，而只是插入\lineskip粘连。

您可以在开始和结束时使用支撑，并抑制行间粘连，这样只要没有异常大的文本，间距就会保留

\tracingonline1
\tracingoutput1

\showboxdepth=4

\parindent=0pt

\newdimen\linewidth
\linewidth=4in

\newdimen\colsep
\colsep=1em

\newdimen\colwidth
\colwidth=0.5\linewidth
\advance\colwidth by -1\colsep

\def\twocols#1#2{%
    \hbox to \linewidth{% 
      \vtop{\hsize=\colwidth
        \hangindent=1em \hangafter=1 \strut#1\nobreak\strut\par}\hfill
      \vtop{\hsize=\colwidth
        \hangindent=1em \hangafter=1 \strut#2\nobreak\strut\par}\hss
    }\par
}

\twocols
  {This is a very long line that will run over}
  {What is wrong with the spacing?}
\nointerlineskip
\twocols
  {What is wrong with the spacing?}
  {This is a very long line that will run over}

\bye

Answer 2

您可以继承最后一行的深度\vtop：

\parindent=0pt

\newdimen\linewidth
\linewidth=4in

\newdimen\colsep
\colsep=1em

\newdimen\colwidth
\colwidth=0.5\linewidth
\advance\colwidth by -1\colsep

\def\twocols#1#2{%
  \par
  \setbox0=\vtop{\hsize=\colwidth
    \hangindent=1em \hangafter=1 #1\par
    \xdef\tpdA{\the\prevdepth}
  }%
  \setbox2=\vtop{\hsize=\colwidth
    \hangindent=1em \hangafter=1 #2\par
    \xdef\tpdB{\the\prevdepth}
  }%
  \edef\tpd{\ifdim\dp0>\dp2 \tpdA \else \tpdB\fi}%
  \hbox to \linewidth{\box0 \hfill \box2}
  \prevdepth=\tpd
}

\twocols
  {This is a very long line that will run over over over over over over over}
  {What is wrong with the spacing?}
\twocols
  {What is wrong with the spacing?}
  {This is a very long line that will run over}

\bye

Answer 3

更新处理了跳行问题。请勿在页面底部附近使用此方法。

\parindent=0pt

\newdimen\linewidth
\linewidth=4in

\newdimen\colsep
\colsep=1em

\newdimen\colwidth
\colwidth=0.5\linewidth
\advance\colwidth by -1\colsep

\def\twocols#1#2{%
    \par
    \hbox to\linewidth
    {%
      \vtop{\hsize=\colwidth
        \hangindent=1em \hangafter=1 #1\par\indent}\hfill
      \vtop{\hsize=\colwidth
        \hangindent=1em \hangafter=1 #2\par\indent}%
    }\kern-\baselineskip\hrule height0pt
    \indent\par
}

\lineskip\maxdimen

\twocols
  {This is a very long line that will run over over over over over over over ppppp}
  {Nothing wrong with
  the spacing !}
\twocols
  {Nothing \smash{\vrule height \baselineskip depth 0pt  width 1pt} wrong with
  the spacing! YYYYYY ppppppp}
  {This is a very long line that will run over}

AAAAAA\smash{\vrule height \baselineskip depth 0pt  width 1pt}

\showboxbreadth \maxdimen \showboxdepth \maxdimen

\tracingoutput1
\bye

---

这是第三种方法。既不使用\prevdepth（\strut后者即使在后面跟着其他东西，也会强制使用\twocols）。

\parindent=0pt

\newdimen\linewidth
\linewidth=4in

\newdimen\colsep
\colsep=1em

\newdimen\colwidth
\colwidth=0.5\linewidth
\advance\colwidth by -1\colsep

\def\twocols#1#2{%
    \par
    \hbox to\linewidth
    {%
      \vtop{\hsize=\colwidth
        \hangindent=1em \hangafter=1 #1\par\indent}\hfill
      \vtop{\hsize=\colwidth
        \hangindent=1em \hangafter=1 #2\par\indent}%
    }\par\kern-\baselineskip\indent\par
}

\twocols
  {This is a very long line that will run over over over over over over jjjjj over}
  {What is wrong with the spacing?}
\twocols
  {What is wrong with the spacing?}
  {This is a very long line that will run over}

\bye

Answer 4

那么，为什么不只是如下这样呢？

\parindent=0pt

\newdimen\linewidth
\linewidth=4in

\newdimen\colsep
\colsep=1em

\newdimen\colwidth
\colwidth=0.5\linewidth
\advance\colwidth by -\colsep

\def\singlebox#1{%
  \vtop{%
    \hsize=\colwidth
    \hangindent=1em \hangafter=1
    \leavevmode #1\par
    \kern -\prevdepth
  }%
}
\def\twocols#1#2{%
    \par
    \hbox to\linewidth
    {%
      \singlebox{#1}\hfill\singlebox{#2}%
    }%
    \prevdepth = 0pt
}

\twocols
  {This is a very long line that will run over over over over over over jjjjj over}
  {What is wrong with the spacing?}
\twocols
  {What is wrong with the spacing?}
  {This is a very long line that will run over}

More text.

% {\tracingall\showlists}

\bye

很明显，由于它“消除”了构造中底线的深度\twocols，因此当文本包含不寻常的下降线时，此解决方案并不适用（egreg 立刻注意到了这一点）。此答案只是为了简化 jfbu 的想法。

一个可能的改进是：

\parindent=0pt

\newdimen\linewidth
\linewidth=4in

\newdimen\colsep
\colsep=1em

\newdimen\colwidth
\colwidth=0.5\linewidth
\advance\colwidth by -\colsep

\def\singlebox#1{%
  \vtop{%
    \hsize=\colwidth
    \hangindent=1em \hangafter=1
    \leavevmode #1\par
    \kern -%
      \ifdim\prevdepth<\maxdepth
        \prevdepth
      \else
        \maxdepth
      \fi
  }%
}
\def\twocols#1#2{%
    \par
    \hbox to\linewidth
    {%
      \singlebox{#1}\hfill\singlebox{#2}%
    }%
    \prevdepth = 0pt
}

\twocols
  {This is a very long line that will run over over over over over over jjjjj over}
  {What is wrong with the spacing?}
\twocols
  {What is wrong with the spacing?}
  {This is a very long line that will run over}

More text.

\twocols
  {This is a very long line that will run over over over over over over jjjjj 
  over $\Bigg|$}
  {What is wrong with the spacing?}
\twocols
  {What is wrong with the spacing?}
  {This is a very long line that will run over}

Still more text.

% {\tracingall\showlists}

\bye

修改后的代码产生的输出是

请注意做页面底部也有效。此外，由于 OP 没有在构造\parskip上方插入粘连\twocols，我也没有；如果需要，可以在 的定义中的命令\vskip\parskip之前添加显式。\hbox\twocols