# Ugly artifacts with pgf-blur and beamer (and poppler)

I am trying to add blur shadows to a beamer presentation using the pgf-blur package. Here is a minimal working example:

\documentclass{beamer}

\usepackage{tikz}

\begin{document}

\begin{frame}
\begin{tikzpicture}
\node[minimum height=1cm, minimum width=3cm,
rounded corners, fill=red!30, blur shadow] {};
\end{tikzpicture}
\end{frame}

\end{document}


Unfortunately, when I try to present my slides using any of the poppler-based renderers (like xpdf, evince, okular, impressive), I get an extremely ugly artifact at the border and especially corners. Here is what it looks like:

Interestingly, the problem goes away if I do the same thing in a \documentclass{article}. Here is a screenshot of the same image without beamer:

Because the problem does not happen with mupdf, this may actually just be a bug in libpoppler. However, libpoppler is so prevalent that I need to find a way to work around it. The fact that the bug goes away without beamer gives me some hope there is a way around this, but I have no idea what beamer might be doing to cause the artifact. I'd also be happy with an alternative to pgf-blur, if there is one.

• You don't need blur here. Beamer has its own shadows and they are hardly distinguishable. – percusse Jan 12 '16 at 1:44
• @percusse Any advice on how to use those shadows in a tikz picture? – user3188445 Jan 13 '16 at 5:31
• Yes it is given in the shadows library which beamer uses – percusse Jan 13 '16 at 5:32
• @percusse You mean like in beamerbaseboxes.sty, the stuff that happens \ifbmb@shadow? It doesn't seem to be using much of a library but rather implementing a lot of the stuff inline with low-level pgf commands... – user3188445 Jan 13 '16 at 5:37
• Is there anything to do with tex.stackexchange.com/questions/226598/… ? – Symbol 1 Jan 15 '16 at 9:43

Here is a workaround:

\documentclass{beamer}

\usepackage{tikz}
\tikzset{
preaction={fill=black,fill opacity=.025,transform canvas={xshift=#1,yshift=-1*#1}},
},
},
}
\begin{document}

\begin{frame}
\begin{tikzpicture}
\node[minimum height=1cm, minimum width=3cm,
rounded corners, fill=red!30,