Size/density of dots used by \dotuline command (ulem package)

Question

I would like to use the \dotuline command (from the ulem package) to create a "fill in the blanks" document.

It gives good results but when the blank becomes small it is hardly noticeable (a single dot in the following MWE):

\documentclass[a4paper,11pt]{article}
\usepackage{ulem}

\begin{document}
A sentence with a ....... to fill.
A sentence with a \dotuline{~~~~~~~} to fill.

A small ... to fill.
A small \dotuline{~~} to fill.
\end{document}

Is there a way to control the size and/or the density of the dots of this command?

Answer 1

Taking the definition of \dotuline from ulem.sty:

\def\dotuline{\bgroup 
  \UL@setULdepth
  \markoverwith{\begingroup
     \advance\ULdepth0.08ex 
     \lower\ULdepth\hbox{\kern.1em .\kern.04em}%
     \endgroup}%
  \ULon}

one can see that the part responsible for the actual dots is \hbox{\kern.1em .\kern.04em}. So it's quite easy to change these values or to create a macro that takes the spacing as argument. For example:

\documentclass[a4paper,11pt]{article}
\usepackage{ulem}

\usepackage{graphicx}

\makeatletter
\def\NewDotuline#1{\bgroup 
  \UL@setULdepth
  \markoverwith{\begingroup
     \advance\ULdepth0.08ex 
     \lower\ULdepth\hbox{.\kern#1}%
     \endgroup}%
  \ULon}

\def\SmallDotuline#1{\bgroup 
  \UL@setULdepth
  \markoverwith{\begingroup
     \advance\ULdepth0.08ex 
     \lower\ULdepth\hbox{\scalebox{0.7}{.}\kern#1}%
     \endgroup}%
  \ULon}
\makeatother

\begin{document}
\pagenumbering{gobble}
A sentence with a ....... to fill.
A sentence with a \dotuline{~~~~~~~} to fill.

A small ... to fill.
A small \dotuline{~~} to fill.


A sentence with a ....... to fill.
A sentence with a \NewDotuline{0em}{~~~~~~~} to fill.

A small ... to fill.
A small \NewDotuline{0em}{~~} to fill.


A sentence with a ....... to fill.
A sentence with a \NewDotuline{-0.1em}{~~~~~~~} to fill.

A small ... to fill.
A small \NewDotuline{-0.1em}{~~} to fill.


A sentence with a ....... to fill.
A sentence with a \SmallDotuline{-0.05em}{~~~~~~~} to fill.

A small ... to fill.
A small \SmallDotuline{-0.05em}{~~} to fill.
\end{document}

Answer 2

Just for the fun of it: a keyval interface to a configurable version of \dotuline.

The command is now called \ULine and you can modify:

• What is printed with the text key. For example, you can use text={\tikz[scale=0.05]\duck;} :D
• The kern inserted before and after the text with pre and pos
• The depth of the underline with depth (you can tweak the depth to make an overline -- I did it with -2ex in the example with text={,})

The values can be changed locally with the optional argument to \ULine or globally with \SetULine.

Result:

Code:

\documentclass[a4paper,11pt]{article}
\usepackage{ulem}
\usepackage{graphicx}
\usepackage{xparse}
\usepackage{tikzducks}
\usepackage{tikzmarmots}

\ExplSyntaxOn
\keys_define:nn { uline } {
  ,text   .code:n       = \cs_set:Nn \uline_text: { #1 }
  ,pre    .dim_set:N    = \l_uline_kern_pre
  ,pre    .initial:n    = 0.1em
  ,pos    .dim_set:N    = \l_uline_kern_pos
  ,pos    .initial:n    = 0.04em
  ,depth  .dim_set:N    = \l_uline_depth
  ,depth  .initial:n    = 0.08ex
}
\NewDocumentCommand{\SetULine}{ m }
  { \keys_set:nn { uline } { #1 } }
\cs_new:Npn \uline_text: { . }
\NewDocumentCommand\ULine
  { o }
  {
    \c_group_begin_token
    \IfValueT { #1 }
      { \keys_set:nn { uline } { #1 } }
    \use:c { UL@setULdepth }
    \markoverwith
      {
       \group_begin:
         \dim_add:Nn \ULdepth { \l_uline_depth }
         \box_move_down:nn { \ULdepth }
           {
             \hbox:n {
               \tex_kern:D \l_uline_kern_pre \scan_stop:
               \uline_text:
               \tex_kern:D \l_uline_kern_pos \scan_stop:
             }
           }
       \group_end:
      }
    \ULon
  }
\ExplSyntaxOff

\begin{document}
\pagenumbering{gobble}

A sentence with a ........ to fill.

A sentence with a \ULine[pre=0pt,pos=0pt]{~~~~~~~} to fill.

A sentence with a \ULine[pre=0pt,pos=-0.1em]{~~~~~~~} to fill.

A sentence with a \ULine[text=\scalebox{0.7}{.},pre=0pt,pos=-0.05em]{~~~~~~~} to fill.

A sentence with a \ULine[depth=-2ex,text={,}]{~~~~~~~} to fill.

A sentence with a \ULine[text={\tikz[scale=0.05]\duck;},pre=-0.05em]{~~~~~~~} to fill.

A sentence with a \ULine[text={\tikz[scale=0.15]\marmot;},pre=-0.05em,depth=1ex]{~~~~~~~} to fill.

\end{document}