Okular does not correctly rasterise the attached PDF depending on the zoom level. The problem is that two rectangles with slightly different width are drawn on top of each other to produce an equal sign. It seems to be an Okular-only issue. (I have not checked that many readers, in particular I haven't checked Adobe Acrobat.) The LaTeX code to produce the PDF can be found here [1]. [1] http://tex.stackexchange.com/questions/168071/tikz-double-line-rasterisation-issue Reproducible: Always Steps to Reproduce: Load the PDF and try different zoom levels. (The 'bad' zoom levels seem to dependent on the screen resolution.) On my netbook (1024x600), the issue appears below 200%. Actual Results: See the attached jpeg.
Created attachment 85887 [details] Problematic PDF
Created attachment 85888 [details] Screenshots at different zoom levels
I can confirm the issue with Okular 0.18.4 and poppler 0.24.3, but I guess it is a poppler bug.
I can still confirm the issue on an Ubuntu 14.04 system, i.e. okular version 0.19 and poppler version 0.24.5. I also tested Christoph's hypothesis with evince, a viewer which also uses the poppler library, and I cannot reproduce the issue. Though, evince has some rendering problems, e.g. the two lines of the equal sign look differently, which lead me to believe that evince's poppler configuration was fine tuned to exactly avoid this problem. Still, even with this fine tuning, it does not render the document in a completely faithful manner. I do not know enough about the internals of Okular and poppler to locate the problem. Is it a poppler configuration issue or a genuine poppler bug?
evince uses poppler but a different engine for rendering. Any rendering issue in a pdf file will almost never be an Okular issue but a poppler one.
I opened a poppler bug: https://bugs.freedesktop.org/show_bug.cgi?id=77904
Closing upstream for now, waiting for resolution on poppler size.
The PDF attached to the Poppler bug is probably not the same as comment #1 (there, it displays blank for me).