[Tex/LaTex] Matching arrowheads in TikZ with math mode arrowheads

arrowstikz-pgf

TikZ is great at drawing diagrams but there is one feature which I find quite annoying and that's the fact that the default arrowhead provided by TikZ does not necessarily respect the math mode in whichever font you are using. I know that
the TikZ library arrows lets you chose between several different types of arrowheads but none of which offers the same arrowhead as the one drawn in math mode.

When drawing a diagram in TikZ I want the arrowheads to match arrowheads drawn by commands like \to or \xrightarrow{foo}.

Does anyone know how to fix this?

As suggested by Andrew Stacey in the comments below, I should really provide you with an example of what I am talking about.

Using the following code:

An arrow tip produced by TikZ:  
\begin{tikzpicture}
\node (A) at (0,0){$A$};
\node (B) at (1,0){$B$.};

\path (A) edge[->] node[midway,above]{$f$} (B);
\end{tikzpicture}

An arrow tip produced by \texttt{amsmath}: $A \xrightarrow{f} B$.

I get the following output:

enter image description here

I want these two arrowheads to be identical.

Best Answer

I have prepared a comprehensive set of arrow tips matching the Computer Modern arrows, and posted it on CTAN (along with some discussion on this issue and some more stuff that might be useful for mathematical diagrams).

My arrow tips are not as precise as Christian's, but they are about as good as one can get using a few line strokes (as opposed to filling a region), and in practice I find the result good enough.

Here is a comparison (Computer Modern above, tikz-drawn arrow below).

\documentclass{article} 
\usepackage{tikz,tikz-cd,graphicx} 
\begin{document} 
\noindent\hspace{2mm} \scalebox{20}{$\hookrightarrow$} 
\vspace{2cm} 
\tikz \draw[line width=8pt,cm right hook-cm to] (0,0) to (7,0); 
\end{document}

enter image description here

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)

[Tex/LaTex] How to establish node-anchor-like points on a (tikz) rectangle path (is there a better method than the one described)

I think that the best way to establish node-like anchors is to use a node. I'm guessing that the annoyance of using an actual node to draw the rectangle is that specifying a node rectangle by its coordinates is a little more complicated than just saying (0,0) rectangle (3,2). So here's some code that puts an invisible (rectangular - but that's only because the default is a rectangle) node around the current path. If the path is more complicated then the node is guaranteed to contain the rectangular bounding box.

Here's the code:

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{fit}
\makeatletter
\tikzset{
  fitting node/.style={
    inner sep=0pt,
    fill=none,
    draw=none,
    reset transform,
    fit={(\pgf@pathminx,\pgf@pathminy) (\pgf@pathmaxx,\pgf@pathmaxy)}
  },
  reset transform/.code={\pgftransformreset}
}
\makeatother

\begin{document}
\begin{tikzpicture}[line width=.5cm]
\draw[thick,green] (-2,-2) -- (4,4);
\draw (0,0) rectangle (3,2) node[fitting node] (rect) {};
\draw[->,red] (5,5) -- (rect.north east);
\draw[->,red] (0,5) -- (rect.north);
\end{tikzpicture}
\end{document}

The green line is to show that the bounding box used is that of the path and not the current picture. The thick lines are to show that the node anchors are on the proper border of the path, not the "theoretical" path[1].

Here's the result:

path with anchors

[1]: With your method of specifying anchors via coordinates, the anchors would be on the "theoretical" path, namely the north west anchor would be at (3,2) not (3 + half line width, 2 + half line width). If you prefer this, it's easy to modify this method to do that.

Edit Now copes with scale=2 as Altermundus asked about. With more complicated transformations then it gets increasingly difficult to keep track since nodes work differently, and it is working on the actual bounding box rather than the path itself. So in those cases, caveat texer.

Best Answer

Related Solutions

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

[Tex/LaTex] How to establish node-anchor-like points on a (tikz) rectangle path (is there a better method than the one described)

Related Question