Tikz node without text

Question

I have a lot of diagrams with shapes where I draw lines between certain points on the boundary of those shapes. With Tikz I can use nodes to draw shapes, and use anchors like "node.west" to draw lines to points at their boundary.

However, I find it annoying to always set empty brackets {} after the node, as I never have text. Also instead of always having to specify "minimum height" and "minimum width", I would rather have a "size" key with a default value. Last, I haven't found a nice way to define custom node shapes that doesn't involve low level PGF code which I know nothing about.

Up to now, I'm just using commands that draw the desired shapes at Tikz coordinates. But then I don't have the possibility to use anchors, which I would find quite neat.

Is there a Tikz equivalent of a node, which isn't designed for putting text, but just shapes? Or is there another solution that is similar to what I want?

Answer 1

There is the key node contents that specifically allows you to drop the empty braces, {}. A minor pitfall is that this key needs to come after the name of the node.

\documentclass[tikz,border=3mm]{standalone}
\begin{document}
\begin{tikzpicture}[circle only/.style={circle,draw,inner sep=2pt,node contents={}}]
 \path node (P) [circle only] ;
 %\path node[circle only] (P)  ; % does not work
 \draw (P.north west) -- ++ (-1,1);
\end{tikzpicture}
\end{document}

For somewhat more advanced options look up the definition of vertex that ships with tikz-feynman.