[Tex/LaTex] How to draw a double-color line with tikz

colortikz-pgf

I would like to draw a rectangle with a double color border: the border should be a line dashed with two alternating colors (blue and red, for example). Is it possible?

Best Answer

As mentionned in Martin's comment, the trick is to draw the line twice. One of the constraints on paths in Tikz/PGF is that the color is global to the path.

Other than drawing a solid line covered by a dashed line, you may draw two dashed lines, with spaces between the dashes, as given by the following example (you can find more information in the Tikz manual) :

\begin{tikzpicture}

\draw[blue,dash pattern= on 3pt off 5pt] (0,0) |- (1,1) to[out=0,in=90] (2,0);
\draw[red,dash pattern= on 3pt off 5pt,dash phase=4pt] (0,0) |- (1,1) to[out=0,in=90] (2,0);

\end{tikzpicture}

The outcome is

two color dashed line

(Following a comment by Caramdir) : The same result can be achieved with a postaction, and the path only has to be specified once :

\draw[postaction={draw,red,dash pattern= on 3pt off 5pt,dash phase=4pt,thick}]
[blue,dash pattern= on 3pt off 5pt,thick] (0,0) |- (1,1) to[out=0,in=90] (2,0);

(Following a request for a rectangle) * I'm not sure this answers the question in the comment *

For a rectangle you would type in the command

\draw[postaction={draw,red,dash pattern= on 3pt off 5pt,dash phase=4pt,thick}]
    [blue,dash pattern= on 3pt off 5pt,thick] (0,0) rectangle (3,2);

This rectangle does not have rounded corners, it is a "normal" rectangle. If ever you do want rounded corners, add rounded corners to the options :

\draw[postaction={draw,red,dash pattern= on 3pt off 5pt,dash phase=4pt,thick,rounded corners}]
    [blue,dash pattern= on 3pt off 5pt,thick,rounded corners] (0,0) rectangle (3,2);
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