Cool Text Highlighting in LaTeX

Question

LaTeX has soul. ConTeXt, of course, has beautifully marked up "sharpie" highlighting, where you can put sweet hightligher under your text for free!

In the pictured example, you can see highlights that not only highlight, but that do it with cool edges that look so good, you can smell fumes! The fearless author says he'll show how that was done in another post; this one shows only how to lay down a straight, yellow box. But, it is possible to do word-wrapped highlighting with cool-shapped boxes within ConTeXt, presumably.

The trouble for me is that getting into the ConTeXt world is steep climb right now, given the state of documentation and the flux of changes, so I need to continue with LaTeX. But the real problem is that now I can't live without the Organic-Looking Highlights of Awesomeness in that picture!

As I said, Non-Organic-Looking Highlights of the Ordinary are easy with the soul package:

\hl{Some awesome text that word wraps fine.}

It just taunts me on the page with its straight lines. So, if I sacrifice word wrapping, I can use PGF/TiKz and create the following macro:

\newcommand\hl[1]{%
    \tikz[baseline,%
      decoration={random steps,amplitude=1pt,segment length=15pt},%
      outer sep=-15pt, inner sep = 0pt%
    ]%
   \node[decorate,rectangle,fill=navcolor,anchor=text]{#1\xspace};%
}%

Which creates something like this:

Now, my color is too dark and my randomness needs adjusting, but you see that a similar effect could be achieved.

My trouble is that I don't understand TeX enough to dig into the Soul package and add the TiKz/PGF goodness that it so sorely needs. So, I leave it to you guys. Anyone want to tackle this?

Or is it yet another piece of fruit, just a touch out of reach, that shall have to wait until ConTeXt settles down?

Answer 1

Much to my surprise, this is doable, by combining TikZ and soul. I don't think I like how it looks (though to each their own), but it was a fun challenge. The idea is to use TikZ to draw the necessary boxes up to line breaks, and then restart each box on a new line. But how to do this? Well, it turns out that soul works by inserting things after every possible hyphenation point (which it calls "syllables", a terminology misuse I find irritating)—importantly, this includes the beginnings and ends of words. And the only time we ever see a line break is after a hyphenation point! This is good: we'll use soul to insert a TikZ node at each syllable break, and then draw them together. For this, we use TikZ's remember picture and overlay options; the former enables you to refer to nodes in the labeled picture from outside, and the latter makes the picture take up no space.

To implement this, we surround each hyphenation unit with two "marks" (TikZ pictures). The "start" mark checks to see if it's on a new line; if it is, it draws the highlighting rectangle from the last recorded start position to the last recorded end position, and then records the new start position. The "stop" mark just records the new stop position. We also have to make sure that at a hyphenation point, the stop position is after the hyphen. And of course, we surround the whole picture with a start position and a stop position. Note that due to the remember picture machinery, you have to compile the document twice.

Here's a working document with ragged highlights:

\documentclass{minimal}
\usepackage{soul}
\usepackage{tikz}
\usetikzlibrary{calc}
\usetikzlibrary{decorations.pathmorphing}

\makeatletter

\newcommand{\defhighlighter}[3][]{%
  \tikzset{every highlighter/.style={color=#2, fill opacity=#3, #1}}%
}

\defhighlighter{yellow}{.5}

\newcommand{\highlight@DoHighlight}{
  \fill [ decoration = {random steps, amplitude=1pt, segment length=15pt}
        , outer sep = -15pt, inner sep = 0pt, decorate
        , every highlighter, this highlighter ]
        ($(begin highlight)+(0,8pt)$) rectangle ($(end highlight)+(0,-3pt)$) ;
}

\newcommand{\highlight@BeginHighlight}{
  \coordinate (begin highlight) at (0,0) ;
}

\newcommand{\highlight@EndHighlight}{
  \coordinate (end highlight) at (0,0) ;
}

\newdimen\highlight@previous
\newdimen\highlight@current

\DeclareRobustCommand*\highlight[1][]{%
  \tikzset{this highlighter/.style={#1}}%
  \SOUL@setup
  %
  \def\SOUL@preamble{%
    \begin{tikzpicture}[overlay, remember picture]
      \highlight@BeginHighlight
      \highlight@EndHighlight
    \end{tikzpicture}%
  }%
  %
  \def\SOUL@postamble{%
    \begin{tikzpicture}[overlay, remember picture]
      \highlight@EndHighlight
      \highlight@DoHighlight
    \end{tikzpicture}%
  }%
  %
  \def\SOUL@everyhyphen{%
    \discretionary{%
      \SOUL@setkern\SOUL@hyphkern
      \SOUL@sethyphenchar
      \tikz[overlay, remember picture] \highlight@EndHighlight ;%
    }{%
    }{%
      \SOUL@setkern\SOUL@charkern
    }%
  }%
  %
  \def\SOUL@everyexhyphen##1{%
    \SOUL@setkern\SOUL@hyphkern
    \hbox{##1}%
    \discretionary{%
      \tikz[overlay, remember picture] \highlight@EndHighlight ;%
    }{%
    }{%
      \SOUL@setkern\SOUL@charkern
    }%
  }%
  %
  \def\SOUL@everysyllable{%
    \begin{tikzpicture}[overlay, remember picture]
      \path let \p0 = (begin highlight), \p1 = (0,0) in \pgfextra
        \global\highlight@previous=\y0
        \global\highlight@current =\y1
      \endpgfextra (0,0) ;
      \ifdim\highlight@current < \highlight@previous
        \highlight@DoHighlight
        \highlight@BeginHighlight
      \fi
    \end{tikzpicture}%
    \the\SOUL@syllable
    \tikz[overlay, remember picture] \highlight@EndHighlight ;%
  }%
  \SOUL@
}
\makeatother

\begin{document}
  Lorem ipsum \highlight{dolor sit amet, consectetur adipis-icing elit, sed do
eiusmod tempor} incididunt ut labore et dolore magna aliqua. Ut enim ad minim
veniam, quis nostrud exercitation \highlight[red]{ullamco $laboris$ nisi ut
aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit} in
voluptate velit esse cillum dolore eu fugiat nulla pariatur.  Excepteur sint
occaecat \highlight[green, draw=blue]{cupidatat non proident,
suntinculpaquiofficiadeseruntmollitanimidestlaborum.
Loremipsumdolorsitametconsecteturadipisicingelitseddoeiusmodtemporincididuntutlabore-etdoloremagnaaliqua.}
I suppose I could write some more text here.
\end{document}

This produces the following output:

There are two formatting modes: \defhighlighter[misc]{color}{opacity}, which sets the fill color to color, the fill opacity to opacity, and styles every highlighter block (via every highlighter) with those plus the misc options. Secondly, for a specific block of highlighted text, you can use \highlight[tikz-opts]{...} to set options locally. These are both demonstrated in the above code.

There are currently four caveats. The first is that this will write one line to your aux file for each syllable break in the highlighted text, in addition to one for the beginning of each, one for the end of each, and one for each line break after a (real or inserted) hyphen. For instance, the example document wrote 222 lines to my aux file. This may or may not be a problem for you, but I'm not sure how to make it better. The second is that strange things happen if you let highlighting extend over a page break. (Although I might be able to fix this one….) The third is that I don't see a way to draw the highlighting in the background. (Because it's drawn so late, the pgfonlayer environment doesn't work.) This is why the text looks faded. You can adjust the opacity value if you don't like this, but I don't see how to avoid it (suggestions?). And the fourth is that I guessed the height of the font, because while I figure this should be a dimension in TeX somewhere, I don't know where (again, suggestions?).

Answer 2

I can't see a difference between the picture you provided and

\documentclass{article}
\usepackage[width=5.05cm]{geometry}
\usepackage{color,soul}

\begin{document}
\noindent\hl{Highlighting} text feels good.
You can draw attention of people to a \hl{word} or perhaps 
\hl{even a whole sentence that spans across multiple lines
in such a way that hyphenation etc. are not affected.}
\end{document}

I suspect getting TeX to draw actual randomly wiggly highlights that work well with line breaks is a lot more work.

Answer 3

If figured that I can adjust my code written for Test if a paragraph has a page break in it? to do underlining and also highlighting. This solution marks the begin and the end of the text with both TikZ and zref marker (the latter to test for page breaks) and draws the lines using tikz between the markers. The current line width is taken into account and new markers are automatically set at every paragraph break. This has the benefit that the normal text typesetting is not influenced at all! I'm working to generalize this (see Place TikZ coordinate or \zlabel at every (base)line and Installing background and foreground page layers with TikZ) and provide a better UI in form of a package as soon I find time.

\documentclass[twoside,11pt]{book}

\usepackage{zref-abspage}
\usepackage{zref-user}
\usepackage{tikz}
\usepackage{atbegshi}
\usetikzlibrary{calc,decorations.pathmorphing}

\makeatletter
\newcommand{\currentsidemargin}{%
  \ifodd\zref@extract{textarea-\thetextarea}{abspage}%
    \oddsidemargin%
  \else%
    \evensidemargin%
  \fi%
}

\newcounter{textarea}
\newcommand{\settextarea}{%
   \stepcounter{textarea}%
   \zlabel{textarea-\thetextarea}%
   \begin{tikzpicture}[overlay,remember picture]
    % Helper nodes
    \path (current page.north west) ++(\hoffset, -\voffset)
        node[anchor=north west, shape=rectangle, inner sep=0, minimum width=\paperwidth, minimum height=\paperheight]
        (pagearea) {};
    \path (pagearea.north west) ++(1in+\currentsidemargin,-1in-\topmargin-\headheight-\headsep)
        node[anchor=north west, shape=rectangle, inner sep=0, minimum width=\textwidth, minimum height=\textheight]
        (textarea) {};
  \end{tikzpicture}%
}


\usepackage{lipsum}
\newcommand\xlipsum[1][]{{\let\par\relax\lipsum*[#1]}}

\tikzset{tikzul/.style={yshift=-.75\dp\strutbox}}

\newcounter{tikzul}%
\newcommand\tikzul[1][]{%
    \begingroup
    \global\tikzullinewidth\linewidth
    \def\tikzulsetting{[#1]}%
    \stepcounter{tikzul}%
    \settextarea
    \zlabel{tikzul-begin-\thetikzul}%
    \tikz[overlay,remember picture,tikzul] \coordinate (tikzul-\thetikzul) at (0,0);% Modified \tikzmark macro
    \ifnum\zref@extract{tikzul-begin-\thetikzul}{abspage}=\zref@extract{tikzul-end-\thetikzul}{abspage}
    \else
        \AtBeginShipoutNext{\tikzul@endpage{#1}}%
    \fi
    \bgroup
    \def\par{\ifhmode\unskip\fi\egroup\par\@ifnextchar\noindent{\noindent\tikzul[#1]}{\tikzul[#1]\bgroup}}%
    \aftergroup\endtikzul
    \let\@let@token=%
}

\newlength\tikzullinewidth

\def\tikzul@endpage#1{%
\setbox\AtBeginShipoutBox\hbox{%
\box\AtBeginShipoutBox
\hbox{%
\begin{tikzpicture}[overlay,remember picture,tikzul]
\draw[#1]
    let \p1 = (tikzul-\thetikzul), \p2 = ([xshift=\tikzullinewidth+\@totalleftmargin]textarea.south west) in
    \ifdim\dimexpr\y1-\y2<.5\baselineskip
        (\x1,\y1) -- (\x2,\y1)
    \else
        let \p3 = ([xshift=\@totalleftmargin]textarea.west) in
        (\x1,\y1) -- +(\tikzullinewidth-\x1+\x3,0)
        % (\x3,\y2) -- (\x2,\y2)
        (\x3,\y1)
       \myloop{\y1-\y2+.5\baselineskip}{%
           ++(0,-\baselineskip) -- +(\tikzullinewidth,0)
       }%
    \fi
;
\end{tikzpicture}%
}}%
}%

\def\endtikzul{%
    \zlabel{tikzul-end-\thetikzul}%
    \ifnum\zref@extract{tikzul-begin-\thetikzul}{abspage}=\zref@extract{tikzul-end-\thetikzul}{abspage}
    \begin{tikzpicture}[overlay,remember picture,tikzul]
        \expandafter\draw\tikzulsetting
            let \p1 = (tikzul-\thetikzul), \p2 = (0,0) in
            \ifdim\y1=\y2
                (\x1,\y1) -- (\x2,\y2)
            \else
                let \p3 = ([xshift=\@totalleftmargin]textarea.west), \p4 = ([xshift=-\rightmargin]textarea.east) in
                (\x1,\y1) -- +(\tikzullinewidth-\x1+\x3,0)
                (\x3,\y2) -- (\x2,\y2)
                (\x3,\y1)
                \myloop{\y1-\y2}{%
                    ++(0,-\baselineskip) -- +(\tikzullinewidth,0)
                }%
            \fi
        ;
    \end{tikzpicture}%
    \else
    \settextarea
    \begin{tikzpicture}[overlay,remember picture,tikzul]
        \expandafter\draw\tikzulsetting
            let \p1 = ([xshift=\@totalleftmargin,yshift=-.5\baselineskip]textarea.north west), \p2 = (0,0) in
            \ifdim\dimexpr\y1-\y2<.5\baselineskip
                (\x1,\y2) -- (\x2,\y2)
            \else
                let \p3 = ([xshift=\@totalleftmargin]textarea.west), \p4 = ([xshift=-\rightmargin]textarea.east) in
                (\x3,\y2) -- (\x2,\y2)
                (\x3,\y2)
                \myloop{\y1-\y2}{%
                    ++(0,+\baselineskip) -- +(\tikzullinewidth,0)
                }
            \fi
        ;
    \end{tikzpicture}%
    \fi
    \endgroup
}

\def\myloop#1#2#3{%
    #3%
    \ifdim\dimexpr#1>1.1\baselineskip
        #2%
        \expandafter\myloop\expandafter{\the\dimexpr#1-\baselineskip\relax}{#2}%
    \fi
}

\makeatother

\begin{document}

text text text text text text text text text text text
text text text text text text text text text text text
text text text text text text text text text text text
text text \tikzul[red]{text text text text text text text text text
text text text text text text text text text text text
text text text text} text text text text text text text
text text text text text text text text text text text
text text text text text text text text text text text

{\tikzset{tikzul/.style={yshift=1ex}}

Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Ut purus elit,
vestibulum ut, placerat ac, adipiscing vitae, felis. Curabitur dictum gravida
mauris. Nam arcu libero, nonummy eget, consectetuer id, vulputate a, magna.
Donec vehicula augue eu neque. Pellentesque habitant morbi tristique senectus
et netus et malesuada fames ac turpis egestas. Mauris ut leo. Cras viverra
metus rhoncus sem. Nulla et lectus vestibulum urna fringilla ultrices. Phasellus
eu tellus sit amet tortor gravida placerat. Integer sapien est, iaculis in, pretium
quis, viverra ac, nunc. Praesent eget sem vel leo ultrices bibendum. \tikzul[line width=1.5\ht\strutbox,semitransparent,yellow]{Aenean
faucibus. Morbi dolor nulla, malesuada eu, pulvinar at, mollis ac, nulla. Curabitur auctor semper nulla. Donec varius orci eget risus. Duis nibh mi, congue
eu, accumsan eleifend, sagittis quis, diam. Duis eget orci sit amet orci dignissim
rutrum.}
text text text text text text text text text text text
text text text text text text text text text text text
text text text text text text text text text text text
test
}

\begin{quote}
text text text text text text text text text text text
text text text text text text text text text text text
text text text text text text text text text text text
text text \tikzul[red]{text text text text text text text text text
text text text text text text text text text text text
text text text text text text text text text text text
text text text text text text text text text text text
text text text text text text text text text text text
text text text text} text text text text text text text
text text text text text text text text text text text
text text text text text text text text text text text
\end{quote}

{\tikzset{tikzul/.style={yshift=.5ex}}

\begin{quote}
text text text text text text text text text text text
text text text text text text text text text text text
\begin{quote}
text text text text text text text text text text text
text text \tikzul[green]{text text text text text text text text text
text text text text text text text text text text text
text text text text 
text text text text text text text
text text text text text text text text text text text
text text text text text text text text text text text
text text text text} text text text text text text text
\end{quote}
text text text text text text text text text text text
text text text text text text text text text text text
\end{quote}

\large
new text text text text text text text text text text text
text text \tikzul[red]{first text text text text text text text text
teXt teXt teXt teXt teXt teXt teXt teXt teXt teXt teXt
teXt teXt teXt teXt teXt teXt teXt teXt teXt teXt teXt
teXt teXt teXt last} teXt teXt teXt teXt teXt teXt teXt
text text text text text text text text text text text
text text text text text text text text text text text

text text text text text text text text text text text
text text text text text text text text text text text
text text \tikzul[red]{text text text text text text text text text
text text\par\noindent text text text text text text text text text
text text text text} text text text text text text text
text text text text text text text text text text text
text text text text text text text text text text text
}

\begin{itemize}
    \item \tikzul{test test test} test
    \item test \tikzul{test test test} test
    \item aa \tikzul{test test test} test
    \item b \tikzul{test test 
text text text text text text text text text text text
text text text text text text text text text text text
text text text text text text text text text text text
        test} test
\end{itemize}

text text text text text text text text text text text
text text text text text text text text text text text
text text text text text text text text text text text
text text text text text text text text text text text
text text \tikzul[red]{text text text text text text text text text
text text

 text text text text text text text text text
text text text text} text text text text text text text
text text text text text text text text text text text
text text text text text text text text text text text

text text text text text text text text text text text
text text text text text text text text text text text
text text \tikzul[red]{text text text text text text text text text
text text

\noindent text text text text text text text text text
\par text text text text} text text text text text text text
text text text text text text text text text text text
text text text text text text text text text text text


\end{document}

Answer 4

This is an old question, but recent question linked to it, so well... The image in the question is from a blog post of mine. Due to some visual artifacts, Andrew thought that the highlighting looked "organic" but those were just straight line.

To set the record straight, here is a ConTeXt solution with organic highlights. The main idea is to use Metapost to draw the highlight; I randomize the line to give the effect that it has been drawn by hand:

\startuseMPgraphic{highlight:random}
    fill
      ((0,RuleDepth) -- (RuleWidth, RuleDepth) --
       (RuleWidth, RuleFactor*RuleThickness) -- (0, RuleFactor*RuleThickness) -- cycle)
       randomized 4bp
        shifted (0,RuleFactor*RuleOffset)
        withcolor RuleColor 
        ;
    setbounds currentpicture to unitsquare xysized(RuleWidth,RuleHeight) ;
\stopuseMPgraphic

\definebar[highlight]
          [
            mp=highlight:random,
            order=background,
            rulethickness=1.1,
            unit=ex,
            offset=-0.25,
            continue=yes,
            color=yellow,
          ]

which gives:

Just to make sure that there are no visual artifacts giving the impression that the highlights are ragged, here is the image when I draw the outline of the highlight (instead of filling it in)

These are too random for my taste. Slightly more subtle is:

or with fill rather than draw:

which is achieved using:

\startuseMPgraphic{highlight:random}
    fill
      ((0 randomized -5pt,RuleDepth) -- (RuleWidth randomized 5pt, RuleDepth) --
       (RuleWidth randomized 5pt, RuleFactor*RuleThickness) -- (0 randomized -5pt, RuleFactor*RuleThickness) -- cycle)
       randomized 2bp
        shifted (0,RuleFactor*RuleOffset)
        withcolor RuleColor 
        ;
    setbounds currentpicture to unitsquare xysized(RuleWidth,RuleHeight) ;
\stopuseMPgraphic

\definebar[highlight]
          [
            mp=highlight:random,
            order=background,
            rulethickness=1.1,
            unit=ex,
            offset=-0.25,
            continue=yes,
            color=yellow,
          ]

Answer 5

Well, this is an old question, but some issues remain unsolved, so I'm trying my hand here. This is a variation of Antal Spector-Zabusky's answer in which I try to handle some of its problems, namely page breaks, and getting the highlighting in the background.

The starting point, as mentioned, is soul. But we use it here exclusively to set tikmarks at the start and end of each hyphenation point. This is done only to get coordinates, no drawing is done at this point.

Drawing is done by tikz AtBeginShipout, based on the full set of tikzmarks made before. It is actually done AtBeginShipoutUpperLeft, which means it is drawn "below" the text.

But, in order to be able to draw the right thing at the right place in the right page, we have to index the tikzmarks. Thus they got names in the form p<page number>.d<decoration number>.<hyphenation point number>. Based on this indexing, we can scan the tikzmarks sequentially, decoration by decoration, page by page. Each line of each "decoration" is handled individually, and at the end of the day, we get (x,y) coordinates for each beginning and end of line, at baseline. First line, last line, middle lines and single lines are handled separately at the moment of drawing, thus allowing for different shapes for each of these cases (this is not used here, but may be quite useful).

The actual use is done by the macro \textdecor[...]{Text} which can take an optional argument which is then appended to the TikZ style at the moment of drawing.

The result:

(page break)

Closer:

The code:

\documentclass[12pt,DIV=8]{scrartcl}
\usepackage{soulutf8}
\usepackage{atbegshi}
\usepackage{etoolbox}
\usepackage{tikz}
\usetikzlibrary{tikzmark,calc,decorations.pathmorphing}


\colorlet{tdcolor}{yellow!35}

\makeatletter

\newlength{\txtdec@depth}
\setlength{\txtdec@depth}{.5ex}
\newlength{\txtdec@height}
\setlength{\txtdec@height}{\f@size pt} % sensible default

\newcounter{txtdec@hyphmark}
\newcounter{txtdec@decormark}
\setcounter{txtdec@decormark}{1}
\newcounter{txtdec@hyphdraw}
\setcounter{txtdec@hyphdraw}{1}
\newcounter{txtdec@decordraw}
\setcounter{txtdec@decordraw}{1}

\newcounter{txtdec@thenextpage}

\newtoggle{txtdec@unfinisheddecor}
\newtoggle{txtdec@stayonpage}
\newtoggle{txtdec@stayondecor}
\newtoggle{txtdec@stayonline}

% from https://tex.stackexchange.com/a/33765/105447
\newcommand{\gettikzxy}[3]{%
  \tikz@scan@one@point\pgfutil@firstofone#1\relax
  \edef#2{\the\pgf@x}%
  \edef#3{\the\pgf@y}%
}

% the drawing macros

\tikzset{%
  defaultdecor/.style={%
    fill=tdcolor,
    decoration = {random steps, amplitude=1pt, segment length=10pt},
    outer sep = -15pt,
    inner sep = 0pt,
    decorate}%
}

\newcommand{\txtdec@draw@all}{%
  \tikzset{thisdecor/.style/.expanded=\csuse{decor@tikz@style@\thetxtdec@decordraw}}%
  \path[defaultdecor, thisdecor]
        ($(\Xbegin,\Ybegin)+(0,-\txtdec@depth)$) rectangle
        ($(\Xend,\Yend)+(0,\txtdec@height-\txtdec@depth)$) ;
}

\newcommand{\txtdec@draw@begin}{%
  \tikzset{thisdecor/.style/.expanded=\csuse{decor@tikz@style@\thetxtdec@decordraw}}%
  \path[defaultdecor, thisdecor]
        ($(\Xbegin,\Ybegin)+(0,-\txtdec@depth)$) rectangle
        ($(\Xlineend,\Ylineend)+(0,\txtdec@height-\txtdec@depth)$) ;
}

\newcommand{\txtdec@draw@middle}{%
  \tikzset{thisdecor/.style/.expanded=\csuse{decor@tikz@style@\thetxtdec@decordraw}}%
  \path[defaultdecor, thisdecor]
        ($(\Xlinebegin,\Ylinebegin)+(0,-\txtdec@depth)$) rectangle
        ($(\Xlineend,\Ylineend)+(0,\txtdec@height-\txtdec@depth)$) ;
}

\newcommand{\txtdec@draw@end}{%
  \tikzset{thisdecor/.style/.expanded=\csuse{decor@tikz@style@\thetxtdec@decordraw}}%
  \path[defaultdecor, thisdecor]
        ($(\Xlinebegin,\Ylinebegin)+(0,-\txtdec@depth)$) rectangle
        ($(\Xend,\Yend)+(0,\txtdec@height-\txtdec@depth)$) ;
}


% using soul to set tikzmarks

\def\SOUL@tdleaders{%
  \stepcounter{txtdec@hyphmark}%
  \tikzmark{p\thepage.d\arabic{txtdec@decormark}.\arabic{txtdec@hyphmark}}%
  \leaders\hrule\@depth\z@\@height\z@\relax
}

\def\SOUL@tdunderline#1{{%
    \setbox\z@\hbox{#1}%
    \dimen@=\wd\z@
    \dimen@i=\SOUL@uloverlap
    \advance\dimen@2\dimen@i
    \rlap{%
      \null
      \kern-\dimen@i
      \SOUL@ulcolor{\SOUL@tdleaders\hskip\dimen@}%
      \hskip\dimen@
    }%
    \unhcopy\z@
  }}

\def\SOUL@tdpreamble{%
  \spaceskip\SOUL@spaceskip
  \setcounter{txtdec@hyphmark}{0}%
  \tikzmark{p\thepage.d\arabic{txtdec@decormark}.begin}%
}
\def\SOUL@tdeverysyllable{%
  \SOUL@tdunderline{%
    \the\SOUL@syllable
    \SOUL@setkern\SOUL@charkern
  }%
  \stepcounter{txtdec@hyphmark}%
  \tikzmark{p\thepage.d\arabic{txtdec@decormark}.\arabic{txtdec@hyphmark}}%
}
\def\SOUL@tdeveryhyphen{%
  \discretionary{%
    \unkern
    \SOUL@tdunderline{%
      \SOUL@setkern\SOUL@hyphkern
      \SOUL@sethyphenchar
    }%
    \stepcounter{txtdec@hyphmark}%
    \tikzmark{p\thepage.d\arabic{txtdec@decormark}.\arabic{txtdec@hyphmark}}%
  }{}{}%
}
\def\SOUL@tdeveryexhyphen#1{%
  \SOUL@setkern\SOUL@hyphkern
  \SOUL@tdunderline{#1}%
  \stepcounter{txtdec@hyphmark}%
  \tikzmark{p\thepage.d\arabic{txtdec@decormark}.\arabic{txtdec@hyphmark}}%
  \discretionary{}{}{%
    \SOUL@setkern\SOUL@charkern
  }%
}
\def\SOUL@tdpostamble{%
  % create an extra mark, vertically displaced, to create an exit condition for the last line
  \stepcounter{txtdec@hyphmark}%
  \raisebox{-5pt}{\tikzmark{p\thepage.d\arabic{txtdec@decormark}.\arabic{txtdec@hyphmark}}}%
  \tikzmark{p\thepage.d\arabic{txtdec@decormark}.end}%
  \stepcounter{txtdec@decormark}%
}
\def\SOUL@tdsetup{%
  \SOUL@setup
  \let\SOUL@preamble\SOUL@tdpreamble
  \let\SOUL@everysyllable\SOUL@tdeverysyllable
  \let\SOUL@everyhyphen\SOUL@tdeveryhyphen
  \let\SOUL@everyexhyphen\SOUL@tdeveryexhyphen
  \let\SOUL@postamble\SOUL@tdpostamble
}
\DeclareRobustCommand*\textdecor[1][]{%
  \csxdef{decor@tikz@style@\thetxtdec@decormark}{#1}%
  \csxdef{decor@fsize@\thetxtdec@decormark}{\f@size pt}%
  \SOUL@tdsetup\SOUL@}


% get the drawing done AtBeginShipout

\AtBeginShipout{%
  \AtBeginShipoutUpperLeft{%
    % getting the number of the next page
    \setcounter{txtdec@thenextpage}{\thepage}%
    \stepcounter{txtdec@thenextpage}%
    % if the current decoration occurs on this page, stay on it
    \iftikzmark{p\thepage.d\arabic{txtdec@decordraw}.\arabic{txtdec@hyphdraw}}{%
      \toggletrue{txtdec@stayonpage}}{}%
    \whileboolexpr{togl {txtdec@stayonpage}}{%
      \begin{tikzpicture}[remember picture, overlay]
        \setlength{\txtdec@height}{\csuse{decor@fsize@\thetxtdec@decordraw}}%
        \iftikzmark{p\thepage.d\arabic{txtdec@decordraw}.begin}{%
          % if current decor begins in current page, get coordinates
          \gettikzxy{(pic cs:p\thepage.d\arabic{txtdec@decordraw}.begin)}{\Xbegin}{\Ybegin}}{%
          % if current decor begins in previous page, set to top left of the page
          \gettikzxy{(current page.north west)}{\Xbegin}{\Ybegin}}%
        \iftikzmark{p\thepage.d\arabic{txtdec@decordraw}.end}{%
          % if current decor ends in current page, get coordinates
          \gettikzxy{(pic cs:p\thepage.d\arabic{txtdec@decordraw}.end)}{\Xend}{\Yend}}{%
          % if current decor ends in future page, set to bottom right of the page
          \gettikzxy{(current page.south east)}{\Xend}{\Yend}}%
        \ifdim\Ybegin=\Yend % the simplest case, a single line
          \txtdec@draw@all
          \stepcounter{txtdec@decordraw}%
        \else % current textdecor has a line break          
          \toggletrue{txtdec@stayondecor}%
          \whileboolexpr{togl {txtdec@stayondecor}}{%
            \gettikzxy{(pic cs:p\thepage.d\arabic{txtdec@decordraw}.\arabic{txtdec@hyphdraw})}{\Xlinebegin}{\Ylinebegin}%
            \edef\Xcurrent{\Xlinebegin}%
            \edef\Ycurrent{\Ylinebegin}%
            \edef\Xnext{\Xcurrent}%
            \edef\Ynext{\Ycurrent}%
            \toggletrue{txtdec@stayonline}%
            \whileboolexpr{togl {txtdec@stayonline}}{%
              \ifdim\Ycurrent=\Ynext
                \stepcounter{txtdec@hyphdraw}%
                % if the following tikzmark exists, we are at a page break
                \iftikzmark{p\arabic{txtdec@thenextpage}.d\arabic{txtdec@decordraw}.\arabic{txtdec@hyphdraw}}{%
                  \edef\Xcurrent{\Xnext}%
                  \edef\Ycurrent{\Ynext}%
                  \gettikzxy{(current page.south east)}{\Xnext}{\Ynext}
                  \togglefalse{txtdec@stayondecor}%
                }{% else, we remain on the same page
                  \iftikzmark{p\thepage.d\arabic{txtdec@decordraw}.\arabic{txtdec@hyphdraw}}{%
                    \edef\Xcurrent{\Xnext}%
                    \edef\Ycurrent{\Ynext}%
                    \gettikzxy{(pic cs:p\thepage.d\arabic{txtdec@decordraw}.\arabic{txtdec@hyphdraw})}{\Xnext}{\Ynext}}{}%
                }%
              \else
                \edef\Xlineend{\Xcurrent}%
                \edef\Ylineend{\Ycurrent}%
                % if we are on the first line of the current decoration
                \ifdim\Ylinebegin=\Ybegin
                  \txtdec@draw@begin
                \else
                  % if we are on the last line of the current decoration
                  \ifdim\Ycurrent=\Yend
                    \txtdec@draw@end
                    \stepcounter{txtdec@decordraw}%
                    \setcounter{txtdec@hyphdraw}{1}%
                    \togglefalse{txtdec@stayondecor}%
                  % if we are in a middle line of the decoration
                  \else
                    \txtdec@draw@middle
                  \fi
                \fi
                \togglefalse{txtdec@stayonline}%  
              \fi
            }%
          }%
        \fi
      \end{tikzpicture}%
      % if the beginning of the next decor does not exist in this page, leave this page
      \iftikzmark{p\thepage.d\arabic{txtdec@decordraw}.begin}{}{%
        \togglefalse{txtdec@stayonpage}}%
      % if the continuation of the current decor exists in the next page, leave this page
      \iftikzmark{p\arabic{txtdec@thenextpage}.d\arabic{txtdec@decordraw}.\arabic{txtdec@hyphdraw}}{%
        \togglefalse{txtdec@stayonpage}}{}% 
    }%
  }%
}

\makeatother

\begin{document}

\vspace*{5cm}

Lorem ipsum \textdecor{dolor sit amet, consectetuer adipiscing}
elit. Ut purus elit, vestibulum ut, placerat ac, adipiscing vitae,
felis. Curabitur dictum gravida mauris. Nam arcu libero, nonummy eget,
consectetuer id, vulputate a, magna. \textdecor[draw=green]{Donec
  vehicula augue eu neque. Pellentesque habitant morbi tristi-que
  senectus et netus et malesuada fames ac -- turpis ---
  egestas. Mauris ut leo. Cras viverra metus rhoncus sem. Nulla et
  lectus vestibulum urna fringilla ultrices.} Phasellus eu tellus sit
amet tortor gravida placerat. Integer sapien est, iaculis in, pretium
quis, viverra ac, nunc. Praesent eget sem vel leo ultrices
bibendum. Aenean faucibus. Morbi dolor nulla, malesuada eu, pulvinar
at, mollis ac, nulla. Curabitur auctor semper nulla. Donec varius orci
eget risus. Duis nibh mi, congue eu, accumsan eleifend, sagittis quis,
diam. Duis eget orci sit amet orci dignissim rutrum.  Nam dui ligula,
fringilla a, euismod sodales, sollicitudin vel, wisi. Morbi auctor
lorem non justo. Nam lacus libero, pretium at, lobortis vitae,
ultricies et, tellus. Donec aliquet, tortor sed accumsan bibendum,
erat ligula aliquet magna, vitae ornare odio metus a mi.  Morbi ac
orci et nisl hendrerit mollis. Suspendisse ut massa.  Nam dui ligula,
fringilla a, euismod sodales, sollicitudin vel, wisi. Morbi auctor
lorem non justo. Nam lacus libero, pretium at, lobortis vitae,
ultricies et, tellus. Donec aliquet, tortor sed accumsan bibendum,
erat ligula aliquet magna, vitae ornare odio metus a mi.  Morbi ac
orci et nisl hendrerit mollis. Suspendisse ut massa.  \textdecor[red,
draw=black]{Nam dui ligula, fringilla a, euismod sodales, sollicitudin
  vel, wisi. Morbi auctor lorem non justo. Nam lacus libero, pretium
  at, lobortis vitae, ultricies et, tellus. Donec aliquet, tortor sed
  accumsan bibendum, erat ligula aliquet magna, vitae ornare odio
  metus a mi.  Morbi ac orci et nisl hendrerit mollis. Suspendisse ut
  massa.  Nam dui ligula, fringilla a, euismod sodales, sollicitudin
  vel, wisi. Morbi auctor lorem non justo. Nam lacus libero, pretium
  at, lobortis vitae, ultricies et, tellus. Donec aliquet, tortor sed
  accumsan bibendum, erat ligula aliquet magna, vitae ornare odio
  metus a mi.  Morbi ac orci et nisl hendrerit mollis. Suspendisse ut
  massa.  Cras nec ante. Pellentesque a nulla.} Cum sociis natoque
penatibus et magnis dis parturient montes, nascetur ridiculus mus.
Aliquam tincidunt urna. Nulla ullamcorper vestibulum
turpis. Pellentesque cursus luctus mauris.

\begin{quotation}
  Lorem ipsum {\large \textdecor[blue]{dolor sit amet, consectetuer
      adipiscing}} elit. Ut purus elit, vestibulum ut, placerat ac,
  adipiscing vitae, felis. Curabitur dictum gravida mauris. Nam arcu
  libero, nonummy eget, consectetuer id, vulputate a, magna.
  \textdecor[green]{Donec vehicula augue eu neque. Pellentesque
    habitant morbi tristi-que senectus et netus et malesuada fames ac
    -- turpis --- egestas. Mauris ut leo. Cras viverra metus rhoncus
    sem. Nulla et lectus vestibulum urna fringilla ultrices.}
  Phasellus eu tellus sit amet tortor gravida placerat.
\end{quotation}

\begin{itemize}
\item Lorem ipsum \textdecor[blue, draw=magenta]{dolor sit amet,
    consectetuer adipiscing} elit.
\item Ut purus elit, vestibulum ut, placerat ac, adipiscing vitae,
  felis. Curabitur dictum gravida mauris. Nam arcu libero, nonummy
  eget, consectetuer id, vulputate a, magna. \textdecor[gray]{Donec
    vehicula augue eu neque. Pellentesque habitant morbi tristi-que
    senectus et netus et malesuada fames ac -- turpis ---
    egestas. Mauris ut leo.}
\end{itemize}

\end{document}

The overall setting is quite flexible, given we draw with tikz on a set of coordinates selected from the tikzmarks. Page breaks work fine (including multiple). The highlighting is drawn below the text, as mentioned before. And the decoration height is responsive to the current font size.

Applications at:

• Box highlighting of text with rounded corners (soul-based)
• Auto-cross lines in framebox (by @marmot)

Ah! Important. Credits here also go to @marmot, for stimulus and ideas on chat.

Answer 6

You are not showing if and how context can do what you want. But in any case there is a major difference: LaTeX uses as engine pdftex while context uses luatex. So moving a context solution to latex would mean moving to lualatex.

In the case of "soul": \hl in soul is basically and \ul (underline) with a large and colored rule. Tweaking soul isn't so difficult: The complete code is about 900 lines. The important part which defines the user command start at line 525. soul splits the input in tokens, syllables, spaces, hyphen and you have to tell it what to do with the pieces. In the case of \ul/\hl eg. \leaders are used. It can be quite fun to change this (in real life you shouldn't redefine the \ul-commands as this will affect \ul. You should define your own new soul command). You can see quite good the "syllables":

 \documentclass{article}
 \usepackage{soul,xcolor}
 \begin{document}
 \hl{highlight} text

 \makeatletter

 \def\SOUL@ulleaders{%
     \leaders\hbox{%
      \textcolor{green}{\rule{2pt}{2.5ex}}%
      \textcolor{red}{\rule{2pt}{2.2ex}}}\relax
 }

 \def\SOUL@uleveryspace#1{%
     \SOUL@ulcolor{%
         #1%
         \leaders\hrule\@depth 0pt\@height\SOUL@ulht
         \hskip\spaceskip
     }%
     \null
 }

 \hl{highlight text}

 \ul{test}
 \end{document}

Answer 7

I thought I had an easy solution to this. I was wrong. I knew that the xcolor package make it easy to color text using \color, and, though I hadn't used it, knew it bragged of being able to put a background color on text also using \colorbox. However, even though the documentation claims that \colorbox acts just like \color it doesn't. Here's my test code:

\documentclass{article}
\usepackage{xcolor}
\begin{document}
{\color{blue}{%
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Praesent
tortor. Suspendisse scelerisque mi non risus.}} Duis vitae ligula eget
nunc fermentum malesuada. Class aptent taciti sociosqu ad litora
torquent per conubia nostra, per inceptos himenaeos.

\vspace{2em}

{\colorbox{yellow}{% highlighted part
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Praesent
tortor. Suspendisse scelerisque mi non risus.}} Duis vitae ligula eget
nunc fermentum malesuada. Class aptent taciti sociosqu ad litora
torquent per conubia nostra, per inceptos himenaeos.
\end{document}

You can see that the highlighted portion (i.e. with the yellow bg color) is not a part of the paragraph anymore, I think because of the use of \leavevmode. Anyway, I've emailed the author with this observation and I'm interested to see what he says.