4

The recommended way (see Section 4.2 here) to place pullback corners in tikz-cd diagrams is using diagonal phantom arrows, as in

\documentclass{article}
\usepackage{tikz-cd}
\usepackage{amssymb}
\begin{document}
\begin{tikzcd}
    A   \arrow[r] 
        \arrow[d] 
        \arrow[dr, phantom, "\lrcorner", very near start] 
&   B   \arrow[d] 
\\  C   \arrow[r] 
&   D  
\\
\end{tikzcd}
\end{document}

However, this isn't great when the diagram deviates too far from the square shape, eg because of long labels:

\documentclass{article}
\usepackage{tikz-cd}
\usepackage{amssymb}
\begin{document}
\begin{tikzcd}
    A   \arrow[r] 
        \arrow[d] 
        \arrow[dr, phantom, "\lrcorner", very near start] 
&   B   \arrow[d] 
\\  CCCC\arrow[r] 
&   DDDD  
\\
\end{tikzcd}
\end{document}

enter image description here

The problem is that the \lrcorner is further from the left arrow than from the upper arrow.

I can adjust that manually with shift right, but I wonder if there's a method that doesn't place the corner on an invisible diagonal of the rectangle, but rather at a fixed distance at a 45 degree angle from the center of the upper left corner?

This answer seems to do something like this, but with tikzpicture instead of tikzcd, and I don't know how to adapt it to tikzcd.

user313032
  • 488
  • 1
    If it denotes something about the A use labels, i.e. |[label=south east:$\lrcorner$]| A. Or pics placed like labels: See 2. and 3.. We could also draw a segment of the node's border if that's better. – Qrrbrbirlbel Jul 02 '23 at 01:30

2 Answers2

4

You can place the \lrcorner symbol as a label for the node. You can set the angle and distance.

enter image description here

\documentclass{article}
\usepackage{tikz-cd}
\usepackage{amssymb}
\begin{document}
\begin{tikzcd}
    |[label={[label distance=-2mm]-45:\lrcorner}]|A   \arrow[r] 
        \arrow[d]  
&   B   \arrow[d] 
\\  CCCC\arrow[r] 
&   DDDD
\end{tikzcd}
\end{document}
Sandy G
  • 42,558
3

You can add whatever tikz code you like with the execute at end picture hook.

\documentclass{article}
\usepackage{tikz-cd}
\usepackage{amssymb}
\begin{document}
\begin{tikzcd}[execute at end picture={\path (\tikzcdmatrixname-1-1) node[below right]{$\lrcorner$};}]
    A   \arrow[r] 
        \arrow[d] 
&   B   \arrow[d] 
\\  CCCC\arrow[r] 
&   DDDD  
\\
\end{tikzcd}
\end{document}

enter image description here

You could also use the pic from the linked answer.