Cases environment discontinuous line in brace [closed]

Question

I have the following equation environment with cases:

\documentclass[preview,border=12pt]{standalone}

\usepackage{amsmath}

\begin{document}
\begin{equation*}
  \operatorname{atan2}(y,x) := \begin{cases}
  \arctan\frac{y}{x} & \mathrm{if}\ x > 0\\
  \arctan\frac{y}{x} + \pi & \mathrm{if}\ x < 0,\ y \geq 0\\
  \arctan\frac{y}{x} - \pi & \mathrm{if}\ x < 0,\ y < 0\\
  +\pi/2 & \mathrm{if}\ x = 0,\ y > 0\\
  -\pi/2 & \mathrm{if}\ x = 0,\ y < 0\\
  0 & \mathrm{if}\ x = 0,\ y = 0
  \end{cases}
\end{equation*}
\end{document}

For some reason, the line of the brace is weirdly dotted:

How can I get a nice continuous line there?

Update:

Here is a screenshot of the same thing in the newest Adobe Acrobat Reader; 400% Zoom:

Update #2:

After zooming in even more, I just realized that the symbols which build the brace are pixelated instead of being smooth vectors like all other font glyphs. What could be the reason for this?

Answer 1

Thanks everyone for your help. I removed all packages of the tempate which I had not used. As a next step, I tried to make a MWE from this.

Made a quick check first: I built the pdf file and the effect was gone!

I have no clue which package or setting it was exactly, but I obviously didnt need it anyhow.