Tikz picture dissapears when zooming pdf above certain percentage

Question

I want some shaded lines, so, as I didn't find any specific command for this, I'm trying to do it with a very thin rectangle. I compile with pdflatex and zooming the pdf makes the lines, and, sometimes, also other tikz pictures in the same page, to disappear above certain high zoom percentage, depending on the code; I provide two options in the following MWE, where I include all the libraries used in the main code. I tested that there is no problem with rectangles with more height, but I need very thin lines.

\documentclass[a4paper,12pt]{report}

\usepackage[spanish]{babel}
\usepackage[utf8]{inputenc} 
\usepackage{times}   
\usepackage{graphicx}
\usepackage{subfig}
\usepackage{float}
\usepackage[hypcap]{caption}
\usepackage{array}
\usepackage{hyperref}
\usepackage{color}
\usepackage[usenames,dvipsnames,x11names]{xcolor}
\usepackage{txfonts}
\usepackage{pifont}
\usepackage[titles,subfigure]{tocloft}  
\usepackage{enumitem} 
\usepackage{fancyhdr}
\usepackage[letterspace=8]{microtype}
\usepackage{etoolbox}
\usepackage{tikz}
\usepackage{pgfkeys}
\usetikzlibrary{calc}
\usepackage{fp}
\usetikzlibrary{fixedpointarithmetic}
\usepackage{ifthen}

\begin{document}
\begin{tikzpicture}[shift=(current page.center), remember picture, overlay, x=1mm, y=1mm,fixed point arithmetic] % All the options I need in the main code for having more than one picture and also some text below them.  

    \pgfmathparse{210}\let\L\pgfmathresult
    \pgfmathparse{297}\let\V\pgfmathresult

    % If I use the following code, both lines disappear at zoom = 250%
    \shade[left color=white,right color=black](-9*\L/16,-3*\V/8-0.15) rectangle +(9*\L/16,0.15);
    \shade[left color=black,right color=white](0,-3*\V/8-0.15) rectangle +(9*\L/16,0.15);

    If I comment the two previous lines and use the following two, when zooming the pdf, first disappears the right line at zoom = 360%, and then the left one, at zoom = 380%  
    %\shade[left color=white,right color=black](-9*\L/16,-3*\V/8-0.15) rectangle (0,-3*\V/8+0.15);
    %\shade[left color=black,right color=white](0,-3*\V/8-0.15) rectangle (9*\L/16,-3*\V/8+0.15);
    % Sometimes dissapear also all the content of the page, text and other pictures.

\end{tikzpicture} 
\end{document}

I wanted to put a "shade" tag, also with the "tikz-pgf", but I don't have reputation for it.

Answer 1

If you zoom in further do they reappear? This is almost certainly an issue with your PDF viewer rather than a problem in what TeX is doing or with the PDF file itself.

There are several good PDF viewers for GNU/Linux (and other systems). Ubuntu's repositories will offer a range of options. I mostly use Okular because it integrates well with Kile and a KDE desktop. Evince is a popular option which integrates well with a Gnome desktop. But there are others, too, so you just have to experiment to find which one you like.

As a bonus, these viewers are all much faster and more responsive than Adobe's acroread and several offer significantly better options for annotation (in PDFs which have not been 'blessed' by an expensive copy of Acrobat).