Ghostly lines in tiled clipped pics

Question

I am trying to tile two clipped pic elements like this.

\documentclass[tikz,border=2mm]{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\tikzset{
  one/.pic = {
    \path[clip] (0,0) -- (1,0) -- (1,1) -- cycle;
    \draw [double=white, draw=black, line cap = rect] (1,0) -- (0.6,0.6); 
    }
  }
\path pic {one} pic[rotate=90,yscale=-1] {one};
\end{tikzpicture}
\end{document}

I am seeing ghostly lines, both at the borders of the pics and where they adjoin.

How do I fix this?

This is an unfortunate feature of double, which does not really draw a double line, but a thick line overlaid with a thiner white line in the middle. See e.g. https://tex.stackexchange.com/q/262756 for a related question. AFAIK there is no really simple working solution, but I might be wrong. — , Nov 12 '19 at 14:20
I tried extending the double lines, but got the same ghost lines, so it seems more of a bug than a feature. Rolling your own double lines seems a reasonable solution (until someone fixes the "feature"). — pheon, Nov 12 '19 at 19:03
I think that the real fix would be to have a function in the graphics drivers that draws true double lines. It may very well exist already, I do not know very much on these things. Anyway, drawing two individual lines has the additional benefit that it does not overpaint things in the back in white, which double does. — , Nov 12 '19 at 19:09

score 2 · Accepted Answer · answered Nov 12 '19 at 15:12

This is an unfortunate feature of double, which does not really draw a double line, but a thick line overlaid with a thinner white line in the middle. There have been many related questions such as this one. Assuming that you do not want to fiddle around with the viewer settings, you could draw the double lines as true double lines using calc. The proposal here draws the double for a single straight stretch, so it is not a true generalization of double. And since you clip anyway you could extend the line in both directions.

\documentclass[tikz,border=2mm]{standalone}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}
\begin{tikzpicture}
\tikzset{
  real double straight line/.style={to path={
  ($(\tikztostart)!#1!90:(\tikztotarget)$) -- 
    ($(\tikztotarget)!#1!-90:(\tikztostart)$)
  ($(\tikztostart)!#1!-90:(\tikztotarget)$) -- 
    ($(\tikztotarget)!#1!90:(\tikztostart)$)}},
  real double straight line/.default=0.5pt, 
  one/.pic = {
    \path[clip] (0,0) -- (1,0) -- (1,1) -- cycle;
    \draw [real double straight line] (1+0.1*0.4,-0.1*0.6) to (1-1.1*0.4,1.1*0.6);
    }
  }
\path pic {one} pic[rotate=90,yscale=-1] {one};
\end{tikzpicture}
\end{document}

Ghostly lines in tiled clipped pics

1 Answers1