# Issues

Issue #229 invalid

# White line at the bottom with xelatex

Nicolas Dudebout
created an issue

I have found a strange behavior but I am not sure where the problem lies. It appears in beamer but not in plain LaTeX so I am reporting it here. You guys can maybe help me redirect the problem somewhere else if you think it is not a beamer problem.

In a nutshell, the problem is the following: When compiling a beamer presentation with xelatex a very thin (maybe 1px) white line appears at the bottom of the presentation.

I have narrowed down the combination of beamer, xelatex, and the version of evince in debian sid as being responsible.

Please find below the results of my investigation:

1. To see the problem, I had to put the PDF in a display mode with black borders and to make sure the bottom of the page was not at the bottom of the screen. I usually could see that on a display in portrait mode or by rotating my landscape mode display with xrandr.

2. I could only see that problem with the version of evince in debian sid and not with the one in debian stable.

3. I have identified that the combination beamer+xelatex was the one giving me problems by compiling the following two files with pdflatex, xelatex, and lualatex respectively. The only of the six combinations giving a problem was beamer+xelatex.

% plain LaTeX
\documentclass{article}

\usepackage{xcolor}

\begin{document}
\oddsidemargin=0pt
\topmargin=0pt
\hoffset=-1in
\voffset=-1in
\lineskip=0pt
\enlargethispage*{245pt}
\hbox{\color{red}\vrule width \paperwidth height \paperheight}
\end{document}

% beamer
\documentclass{beamer}

\setbeamercolor{normal text}{fg=white, bg=red}

\begin{document}
\frame{}
\end{document}


Let me know if you have any questions or need more details.

While TeX's 'native' DVI format has certain requirements about rounding, the PDF spec does not. This means that depending upon zoom and PDF renderer there may be artefacts dues to 'out by one' issues. At the same time, the construction of beamers coloured boxes is a complex business, as there are several layers present, even if you don't see them. This increases the chances of rounding issues.
I've checked with a few viewers, and I suspect that Poppler (the PDF library used by Evince) is the culprit here: I can see a border using the TeXworks viewer (also uses Poppler) with all engines at maximum zoom, but not otherwise. As such, this is not something which can be fixed at the beamer end, sorry.