line-breaking
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Is there a way to measure the remaining space of a line of text?
I have some text and want to put a \hrulefill at the end following by a period. However, if the text of the line comes too close to the end of the line, the rule is omitted and just a period results — or — a new line is created, the rule is omitted, and the line begins with a period.
How can I determine if there is enough space at the end of the line for a sizeable enough hrulefill of some specified length?
The answer to the question as posted is a bit fuzzy
Spaces tend to have a glue component that makes predicting their actual width rather hard unless you remove the glue by using \spaceskip & \xspaceskip
Do you really mean 'restrict' or do you mean 'expand'? If there is too much text for 3cm, there is no way to meet the requirements.
The three words, when on one line, will have two intermediate spaces. When on two lines, there will be only one space. It will be quite difficult to make sure the total used space in both cases is identical (in fact, I no idea how to do that in TeX82).
Do you really want the extra room to be filled with \hfill?
Anyway, you could try something like this:
\newdimen\mydimen
\mydimen=3cm
\setbox0=\hbox {Lorem Ipsum Dolor}\advance\mydimen-\wd0 \unhbox0\hskip\mydimen
which may or may not give you something that is exactly 3cm, depending on the rest of the paragraph.
A much more precise solution would be possible using node processing in LuaTeX, but there are not that many hooks in TeX82's line breaking routine that can really alter its behaviour.
If you need to break the underlined space with given size to two parts at the end of the line (sum of the parts is approximately the given size) then there is a solution:
\newcount\tmpnum \newdimen\tmpdim
\def\uelement{\hbox{\vrule height-1pt depth1.4pt width5pt}\penalty0
\hskip0pt minus.1pt \relax}
\def\softelement{\leaders\vrule height-1pt depth1.4pt\hskip 0pt plus5pt\relax}
\def\underlined#1{\bgroup
\tmpdim=#1 \divide\tmpdim by327680 \tmpnum=\tmpdim
\leavevmode \softelement
\loop \ifnum\tmpnum>0\advance\tmpnum by-1 \uelement \repeat
\softelement \egroup
}
First \underlined{5cm} second.
First \underlined{20cm} second.
\bye
The code above implements the type 2 of the breakable blanks, as mentoned in the Update 3 of the question. The type 3 can be simply implemented by adding the \ufill macro:
\def\ufill{\leaders\vrule height-1pt depth1.4pt \hfill}.
First \underlined{5cm}\ufill second.
First \underlined{20cm}\ufill second.
Best Answer
How about the following (using ideas from the command
\qedin amsart.cls):That guarantees you at least 1em of hrulefill (you can change that 1em to some other length, of course), and prevents the hrulefill from being on a line by itself. You'd just put the command
\myrulefillat the end of your paragraph.