[Tex/LaTex] Draw a path with a filled diamond at the beginning

tikz-pgf

My question is similar to this one, but I am trying to draw a simple black filled diamond at the beginning of a path, just like in the UML aggregate notation. Here is a minimal working example:

\documentclass{standalone}
\usepackage{tikz}

\usetikzlibrary{shapes, arrows, chains, decorations.markings,intersections,calc}

\begin{document}
    \begin{tikzpicture}
        \node (a) at (0,0) {a};
        \node (b) at (2,0) {b};
        \path (a.east) to node [near start, yshift=1em] {} (b.west); 
        \draw [<-,>=diamond] (a.east) -- (b.west);
    \end{tikzpicture}
\end{document}

~~but this produces a path with a diamond that has an arrow at the front, how do I get rid of the arrow?~~

E.g. turn <>----> into <>----

Update:

It seems I this behaviour is caused by the tikzset from this question, which I still had in my code. After removing it, I got the desired behaviour. So I change my question: What causes the arrow had to appear or disappear, and how can I change between both versions?

Update 2:
I have updated the question with a MWE and changed the explanation to avoid some of the confusion. The MWE actually produces the desired result of my original question and I am not able to reproduce the problem which I described in the cancelled text. Given all the confusion I think the actual question is this:

How can I produce each of the following UML variants for aggregation see here:

<>---- (this is produced by my MWE)
<>---> (arrow at right end)
<>---* (circle at right end)

Best Answer

You can make use of the arrows and arrows.meta libraries of TikZ. See section 16 in the TikZ Manual. Using this approach you can customize the length, width etc. of the arrow tips as well.

\documentclass[tikz,border=2pt]{standalone}
\usepackage{tikz}

\usetikzlibrary{arrows,arrows.meta}

\begin{document}
  \begin{tikzpicture}
    \node (a) at (0,0) {a};
    \node (b) at (2,0) {b};
    \draw [{Diamond}-] (a.east) -- (b.west);

    \begin{scope}[yshift=-1cm]
      \node (a) at (0,0) {a};
      \node (b) at (2,0) {b};
      \draw [{Diamond}-{Stealth}] (a.east) -- (b.west);
    \end{scope}

    \begin{scope}[yshift=-2cm]
      \node (a) at (0,0) {a};
      \node (b) at (2,0) {b};
      \draw [{Diamond}-{Circle}] (a.east) -- (b.west);
    \end{scope}
  \end{tikzpicture}
\end{document}

This gives the output

Output

Related Solutions

[Tex/LaTex] Rotate a node but not its content: the case of the ellipse decoration

The source of the difficulty is that ellipses are constructed in a particular way in TikZ. They are paths that start from the x-axis and proceed counter-clockwise around their centre. The vast majority of the time, the exact parametrisation doesn't matter. You appear to have found the one situation where it does!

In the actual question, you only want to be able to mirror the ellipse, and so draw it starting from the negative x-axis (the title of the question suggests a more flexible approach). That's actually not too hard since we can exploit the symmetry of the ellipse. The key is to provide it with a negative x-radius, since then it will start from the negative x-axis (and proceed clockwise, but we could correct for that by negating the y-radius as well). To do this, we interrupt the call from the node shape to the drawing command and flip the sign of the x-radius. The simplest way to do this is to redefine the \pgfpathellipse macro to do the negation and then call the original macro. The following code does this.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{decorations,shapes,decorations.markings}
\makeatletter
\let\origpgfpathellipse=\pgfpathellipse
\def\revpgfpathellipse#1#2#3{%
  #2%
  \pgf@xa=-\pgf@x
  \origpgfpathellipse{#1}{\pgfqpoint{\pgf@xa}{0pt}}{#3}}
\makeatother

\tikzset{
  reversed ellipse/.style={
    ellipse,
    reverse the ellipse%
  },
  reverse the ellipse/.code={
    \let\pgfpathellipse=\revpgfpathellipse
  }
}
\begin{document}
\begin{tikzpicture}
\node[ellipse,
  draw,
  postaction={
    decorate,
    decoration={
      markings,
      mark=at position 1 with {
        \arrow[line width=5pt,blue]{>}
      }
    }
  }
] at (0,0) {hello world};

\node[reversed ellipse,
  draw,
  postaction={
    decorate,
    decoration={
      markings,
      mark=at position 1 with {
        \arrow[line width=5pt,blue]{>}
      }
    }
  }
] at (0,-2) {hello world};
\end{tikzpicture}

\end{document}

Here's the result:

rotated ellipse

(the arrow got clipped, but you can see where it lies)

TikZ-PGF – Decorating Path with Open Diamond Arrow Tip That Bends

Here's a very over the top approach that places a coordinate at a specified location along the path, places a circle with a specified diameter on that coordinate, calculates the intersections of the curve and the circle, and then draws a diamond between the two intersections.

Drawbacks: The diamonds will have slightly different sizes, depending on the curvature of the original path. The original path isn't interrupted, instead the diamonds are just drawn on top. With the current implementation, while you can have several diamonds on the same path, the options like diamond ratio, diamond length, and every diamond will apply to all diamonds equally.

\documentclass{standalone}
\usepackage{tikz}

\tikzset{
    diamond helpers/.code={
        \path [draw,name path=circle] (middle) circle [radius=0.1cm];
    },
    diamond/.style={
        decoration={
            markings,
            mark=at position #1 with {
                \coordinate (middle);
                \path [name path=circle] (middle) circle [radius=0.5*\diamondlength];
                \draw [every diamond, name intersections={of=curve and circle}]
                    (intersection-1) -- 
                    ($($(intersection-1)!0.5!(intersection-2)$)!\diamondaspect!90:(intersection-2)$) -- 
                    (intersection-2) -- 
                    ($($(intersection-1)!0.5!(intersection-2)$)!\diamondaspect!-90:(intersection-2)$) -- 
                    cycle;}
        },
        postaction=decorate,
        name path global=curve
    },
    diamond/.default=0.5,
    diamond aspect/.store in=\diamondaspect,
    diamond aspect=0.75,
    diamond length/.store in=\diamondlength,
    diamond length=0.2cm,
    every diamond/.style={draw,fill=white}
}


\usetikzlibrary{decorations.markings,intersections,calc}
\begin{document}
 \begin{tikzpicture}
*  \draw [diamond, diamond=0.1] (0,0) to [out=70, in=100] (1,-1);  
 \end{tikzpicture}
\end{document}

Best Answer

Related Solutions

[Tex/LaTex] Rotate a node but not its content: the case of the ellipse decoration

TikZ-PGF – Decorating Path with Open Diamond Arrow Tip That Bends

Related Question