Philippe Drix made me look into why his borders don't show up properly in Acrobat Reader and his printer.
He specified border widths as 0.002cm: 0.002cm = 0.0567pt = 0.02mm At 600dpi one dot/pixel is 1/600in = 0.00166666in = 0.12pt = 0.0423mm So the border is less than half a pixel wide at 600dpi which is the nominal resolution for most laser printers today. Even at 1200dpi you don't have a full pixel, yet. Digging into the source code, I found out: In FOP 0.20.5 horizontal and vertical lines are painted as rectangles (0.056pt wide). In FOP 0.92beta we're painting these lines as lines (0.056pt wide). So it appears that Acrobat Reader handles the two differently. Apparently, it cannot be said that FOP does something wrong per se. But the question pops up if we should change the way we paint horizontal and vertical lines as part of our border painting code. There's another thing. PDF allows to specify "0" as line width which should result in 1 pixel on the target device. From the PDF Reference: "However, some devices cannot reproduce 1-pixel lines, and on high-resolution devices, they are nearly invisible. Since the results of rendering such zero-width lines are device-dependent, their use is not recommended." It would also be questionable how exactly we would determine when to use "0" as line width. Probably not the best of ideas. WDYT? Jeremias Maerki
