[Tex/LaTex] Using geom_segment dashed line has odd behavior when using tikz device

knitrtikz-pgf

My example is:

\documentclass[12pt]{article}
\begin{document}
<<eg, dev='tikz', size='normalsize', echo=FALSE, message=FALSE, warning=FALSE, sanitize=TRUE>>=
require(ggplot2)
p1 <- ggplot() + geom_segment(aes(x = 1, y = 1, xend = 2, yend = 2),
                              linetype= 2)
p1
@
\end{document}

Which generates a dashed line (when using other graphics devices). When using tikz, there is a thin black line sitting underneath the dashed line. Any ideas as to how to get rid of this?

Best Answer

I have worked out a patch solution for this. Use geom_path to replace the misbehaving geoms. e.g.

    p1 + geom_path(data=data.frame(x=c(1, 2),
                          y=c(1, 2)),
          aes(x=x, y=y), linetype=2)

Related Solutions

[Tex/LaTex] TikZ zero-width line with dashed line

Drawing and filling causes the issue, only drawing works as expected:

\documentclass{article}
\usepackage{tikz}
\usepackage[active,tightpage,psfixbb]{preview}
\PreviewEnvironment{pgfpicture}
\setlength\PreviewBorder{0pt}

\begin{document}
  \begin{tikzpicture}[x=1pt,y=1pt]
    \definecolor[named]{drawColor}{gray}{0}
    \definecolor[named]{fillColor}{rgb}{0,0,0}

    \path[
      draw=drawColor,
      line width= 0.6pt,
      dash pattern=on 1pt off 3pt,
      % line join=round,
      line cap=round,
      % fill=fillColor,
    ]
      ( 21.13, 19.75) -- (132.49,132.50);
  \end{tikzpicture}
\end{document}

Remarks:

With a straight line, line join does not make too much sense, therefore I have changed it to line cap.
0 is three bytes shorter than 0.00.

The the fill color is given, also a fill operation is applied to the path as can be shown in the nondegenerated case of a triangle. The example also shows that line join can be used and has its expected effect:

\documentclass{article}
\usepackage{tikz}
\usepackage[active,tightpage,psfixbb]{preview}
\PreviewEnvironment{pgfpicture}
\setlength\PreviewBorder{0pt}

\begin{document}
  \begin{tikzpicture}[x=1pt,y=1pt]
    \definecolor[named]{drawColor}{gray}{0}
    \definecolor[named]{fillColor}{rgb}{0,0,0}

    \path[
      draw=drawColor,
      line width= 0.6pt,
      dash pattern=on 1pt off 3pt,
      line join=round,
      line cap=round,
      fill=red,
    ]
      (20, 20) -- (60, 60) -- (60, 20) -- cycle;
  \end{tikzpicture}
\end{document}

[Tex/LaTex] TikZ: double line, one dashed

Double line with clipping

The following example draws first a dashed double line between the nodes. Then it clips the lower part and draws a solid double line overprinting the lower dashed line. Since my PDF viewer shows some artifacts at some zoom levels, the inner area is filled with white again.

\documentclass{article}
\usepackage{tikz}

\begin{document}
  \begin{tikzpicture}
    \node (A) at (0, 0) {A};
    \node (B) at (3, 1) {B};
    \draw[double, dashed] (A) -- (B);
    \begin{scope}
      \clip (current bounding box.south west) --
            (A.center) -- (B.center) --
            (current bounding box.south east) -- cycle;
      \draw[double] (A) -- (B);
    \end{scope}
    \draw[
      white,
      line width=0.6pt, % default double distance
      shorten <=-.1pt,
      shorten >=-.1pt,
    ] (A) -- (B);
    % removes some leftover artifacts in the middle
  \end{tikzpicture}
\end{document}

Decoration

The following example implements the double line via the decoration interface. It's one of my first tries, thus there are some restrictions:

Only straight unconnected line segments are supported.
cycle does not work.
The line segments should not be too short.

But is also implements a feature for dashed lines, AFAIK missing in TikZ:

The dashed lines start and ends with the solid phase.

Example file:

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{decorations}

\pgfdeclaredecoration{dashsoliddouble}{initial}{
  \state{initial}[width=\pgfdecoratedinputsegmentlength]{
    \pgfmathsetlengthmacro\lw{.3pt+.5\pgflinewidth}
    \begin{pgfscope}
      \pgfpathmoveto{\pgfpoint{0pt}{\lw}}%
      \pgfpathlineto{\pgfpoint{\pgfdecoratedinputsegmentlength}{\lw}}%
      \pgfmathtruncatemacro\dashnum{%
        round((\pgfdecoratedinputsegmentlength-3pt)/6pt)
      }
      \pgfmathsetmacro\dashscale{%
        \pgfdecoratedinputsegmentlength/(\dashnum*6pt + 3pt)
      }
      \pgfmathsetlengthmacro\dashunit{3pt*\dashscale}
      \pgfsetdash{{\dashunit}{\dashunit}}{0pt}
      \pgfusepath{stroke}
      \pgfsetdash{}{0pt}
      \pgfpathmoveto{\pgfpoint{0pt}{-\lw}}%
      \pgfpathlineto{\pgfpoint{\pgfdecoratedinputsegmentlength}{-\lw}}%     
      \pgfusepath{stroke}
    \end{pgfscope}
  }
}

\begin{document}
  \begin{tikzpicture}
    \node (A) at (0, 0) {A};
    \node (B) at (3, 1) {B};
    \node (C) at (3, 2) {C};
    \node (D) at (1, 2) {D};
    \draw[decoration={dashsoliddouble}, decorate]
      (A) -- (B) -- (C) -- (D) -- (A)
    ;
  \end{tikzpicture}
\end{document}