Defining a custom TikZ arrowtip (circle with plus)
I couldn't see how to combine existing arrows but you can modify the definition of Circle easily enough:
\documentclass[border=1pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows.meta}
\makeatletter
\pgfdeclarearrow{
name = CircleP,
defaults = {
length = +2.39365pt +3.191538,
width' = +0pt 1,
line width = +0pt 1 1,
},
setup code = {
% Cap the line width at 1/2th of the length
\[email protected]\pgfarrowlength
\ifdim\pgf@x<\pgfarrowlinewidth
\pgfarrowlinewidth\pgf@x
\fi
\ifpgfarrowreversed
\pgfarrowssetlineend{\pgfarrowlength\advance\pgf@x by-.5\pgfarrowlinewidth}
\else
\pgfarrowssetlineend{.5\pgfarrowlinewidth}
\fi
\pgfarrowssettipend{\pgfarrowlength}
% The hull:
\pgfarrowsupperhullpoint{\pgfarrowlength}{.25\pgfarrowwidth}
\pgfarrowsupperhullpoint{.75\pgfarrowlength}{.5\pgfarrowwidth}
\pgfarrowsupperhullpoint{.25\pgfarrowlength}{.5\pgfarrowwidth}
\pgfarrowsupperhullpoint{0pt}{.25\pgfarrowwidth}
\ifpgfarrowharpoon%
\pgfarrowshullpoint{0pt}{-.5\pgfarrowlinewidth}
\pgfarrowshullpoint{\pgfarrowlength}{-.5\pgfarrowlinewidth}
\fi%
% The following are needed in the code:
\pgfarrowssavethe\pgfarrowlinewidth
\pgfarrowssavethe\pgfarrowlength
\pgfarrowssavethe\pgfarrowwidth
},
drawing code = {
\pgfsetdash{}{+0pt}
\ifpgfarrowroundjoin\pgfsetroundjoin\else\pgfsetmiterjoin\fi
\ifdim\pgfarrowlinewidth=\pgflinewidth\else\pgfsetlinewidth{+\pgfarrowlinewidth}\fi
\ifpgfarrowharpoon
\pgfpathmoveto{\pgfqpoint{\pgfarrowlength\advance\pgf@x
by-.5\pgfarrowlinewidth}{0pt}}
{%
\[email protected]\pgfarrowlength
\advance\pgf@xa by-.5\pgfarrowlinewidth
\pgftransformxscale{+\the\pgf@xa}
\[email protected]\pgfarrowwidth
\advance\pgf@xa by-.5\pgfarrowlinewidth
\pgftransformyscale{+\the\pgf@xa}
\pgfpathmoveto{\pgfqpoint{-.5\pgfarrowlength}{0pt}}
\pgfpathlineto{\pgfqpoint{.5\pgfarrowlength}{0pt}}
\pgfpatharc{0}{180}{1pt}
}
\pgfpathclose
\else%
\pgfpathmoveto{\pgfqpoint{.25\pgfarrowlength}{0pt}}
\pgfpathlineto{\pgfqpoint{.75\pgfarrowlength}{0pt}}
\pgfpathmoveto{\pgfqpoint{.5\pgfarrowlength}{.25\pgfarrowlength}}
\pgfpathlineto{\pgfqpoint{.5\pgfarrowlength}{-.25\pgfarrowlength}}
\pgfpathellipse{\pgfqpoint{.5\pgfarrowlength}{0pt}}{\pgfqpoint{.5\pgfarrowlength\advance\pgf@x
by-.5\pgfarrowlinewidth}{0pt}}{\pgfqpoint{0pt}{.5\pgfarrowwidth\advance\pgf@y
by-.5\pgfarrowlinewidth}}
\fi
\ifpgfarrowopen\pgfusepathqstroke\else\ifdim\pgfarrowlinewidth>0pt\pgfusepathqfillstroke\else\pgfusepathqfill\fi\fi
},
parameters = {
\the\pgfarrowlinewidth,%
\the\pgfarrowlength,%
\the\pgfarrowwidth,%
\ifpgfarrowharpoon h\fi%
\ifpgfarrowopen o\fi%
\ifpgfarrowroundjoin j\fi%
},
}
\tikzset{circleplus/.tip={
CircleP[open]}}
\begin{document}
\begin{tikzpicture}
\draw [-circleplus] (0,0) -- +(1,0);
\end{tikzpicture}
\end{document}
You could probably define a new arrow tip, as described in Custom arrow tip with arrows.meta
TikZ library
If you don't need the full power of declaring a new arrow, you could just use a marking:
\documentclass[tikz, border=2pt]{standalone}
\usetikzlibrary{decorations.markings}
\tikzset{
-circleplus/.style = {
decoration={markings,
mark=at position 1 with
{\draw[fill=white] (-2pt,0) circle (2pt);
\draw[-] (-3pt,0) -- (-1pt,0) (-2pt,1pt) -- (-2pt,-1pt);
}
},
postaction={decorate}
}
}
\begin{document}
\begin{tikzpicture}
\draw[-circleplus] (0,0) .. controls (.5,0) .. (1,1);
\end{tikzpicture}
\end{document}
This won't combine with other arrow tips in the usual way, but you can still add an arrow tip at the other end using, e.g., \draw[-circleplus, <-] ...
. You'd have to define a separate command for circleplus-
if you want to use that.
@David Carlisle said that he
couldn't see how to combine existing arrows
but he definitely know how: put things together and apply negative spaces.
\tikzset{circleplus/.tip={.
Circle[open,length=0 10,sep=0 -7.5]
Rectangle[length=0 5,width=0 1,sep=0 -3]
Rectangle[length=0 1,width=0 4]
}}