# arrows sloped on a tikz edge aren't straight

When using \underleftarrow on an equation sloped on an edge, the arrow does not look straight. Here is an example:

\documentclass{article}
\usepackage{tikz}
\usepackage{amsmath}

\begin{document}
\begin{tikzpicture}
\node (a) at (0,0)  {a};
\node (b) at (2, 8) {b};
\draw (a) to node[above,sloped]
{$$\underleftarrow{xxxxxxxxxxxxxxxxxxxxxxxxxxx}$$} (b);
\end{tikzpicture}
\end{document}


Screenshot:

How can I fix it?

• When I zoom into a pdf that was generated from your source, they become straighter and straighter. I suspect this is just caused by aliasing. You sometimes also see it with compound mathematical delimiters: on the screen you can see the joins but when you print them you can't. – user10274 Feb 22 '17 at 4:22
• You should be aware that \underleftarrow is produced by connecting a number of dashes; when rotation is involved, these small parts can appear as forming a jagged line, but this is due to the PDF viewer trying to snap to the raster (remember the screen has a much lower resolution than a printer). – egreg Feb 22 '17 at 9:48

If you want to solve this problem once and for all, it is not hard to switch to TikZ's own arrows

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

\begin{document}
\begin{tikzpicture}
\node (a) at (0,0)  {a};
\node (b) at (2, 8) {b};
\draw (a) to node(c)[above=10,sloped]{$xxxxxxxxxxxxxxxxxxxxxxxxxxx$}(b);
\draw[->](c.south east)--(c.south west);
\end{tikzpicture}
\end{document}