Make TikZ arrow curvier

Question

I have this code,

\documentclass{article}

\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
    \draw[very thick, step = 2] (0, 0) grid (6, 6);

    \node[circle, fill=blue] (a) at (2, 0) {};
    \node[circle, fill=blue] (b) at (4, 0) {};

    \node[circle, fill=blue] (c) at (0, 2) {};
    \node[circle, fill=blue] (d) at (2, 2) {};
    \node[circle, fill=blue] (e) at (4, 2) {};

    \node[circle, fill=blue] (f) at (0, 4) {};
    \node[circle, fill=blue] (g) at (2, 4) {};
    \node[circle, fill=blue] (h) at (4, 4) {};

    \path[very thick, draw=red, ->]
        (a) edge node [right] {} (c)
        (c) edge[bend left] node [right] {} (d)
        (d) edge[bend right] node [right] {} (g)
        (g) edge node [right] {} (b)
        (b) edge[bend left] node [right] {} (f)
        (h) edge[bend left] node [right] {} (e)
        (e) edge node [right] {} (a);
\end{tikzpicture}
\end{document}

which produces the following diagram:

I have used the code from this question to make the arrows bendy, but ideally I would like the arrow that goes from node (b) to node (f) to be even curvier, and bend around the outside of the grid. What would be a good way to go about this?

Also, is there a way to create the nodes on the points of the grid, without explicitly giving the coordinates (ie. based on the size of the grid and the step size)? So that if I reshape the grid the nodes change accordingly.

Answer 1

\documentclass{article}

\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
    \draw[very thick, step = 2] (0, 0) grid (6, 6);

    \node[circle, fill=blue] (a) at (2, 0) {};
    \node[circle, fill=blue] (b) at (4, 0) {};

    \node[circle, fill=blue] (c) at (0, 2) {};
    \node[circle, fill=blue] (d) at (2, 2) {};
    \node[circle, fill=blue] (e) at (4, 2) {};

    \node[circle, fill=blue] (f) at (0, 4) {};
    \node[circle, fill=blue] (g) at (2, 4) {};
    \node[circle, fill=blue] (h) at (4, 4) {};

    \path[very thick, draw=red, ->]
        (a) edge node [right] {} (c)
        (c) edge[bend left] node [right] {} (d)
        (d) edge[bend right] node [right] {} (g)
        (g) edge node [right] {} (b)
        (b) edge[out=245, in=180, looseness=2] node [right] {} (f)
        (h) edge[bend left] node [right] {} (e)
        (e) edge node [right] {} (a);
\end{tikzpicture}
\end{document}

EDIT

Just a matter of adjusting the outwards angle from b as 225 degrees and the inwards angle at f as 225 degrees, the looseness controls the flexibility of the curve -- feel free to experiment

\documentclass{article}

\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
    \draw[very thick, step = 2] (0, 0) grid (6, 6);

    \node[circle, fill=blue] (a) at (2, 0) {};
    \node[circle, fill=blue] (b) at (4, 0) {};

    \node[circle, fill=blue] (c) at (0, 2) {};
    \node[circle, fill=blue] (d) at (2, 2) {};
    \node[circle, fill=blue] (e) at (4, 2) {};

    \node[circle, fill=blue] (f) at (0, 4) {};
    \node[circle, fill=blue] (g) at (2, 4) {};
    \node[circle, fill=blue] (h) at (4, 4) {};

    \path[very thick, draw=red, ->]
        (a) edge node [right] {} (c)
        (c) edge[bend left] node [right] {} (d)
        (d) edge[bend right] node [right] {} (g)
        (g) edge node [right] {} (b)
        (b) edge[out=225, in=225, looseness=2] node [right] {} (f)
        (h) edge[bend left] node [right] {} (e)
        (e) edge node [right] {} (a);
\end{tikzpicture}
\end{document}

Answer 2

Here's a method using the hobby package to draw the curve through a point off the grid.

Some notes on this code:

• I've automated the node placement by using a loop, this has added an extra node at (0,0) which could be removed if it isn't wanted but leaving it in is slightly simpler code. This also meant that I standardised the node names a little.
• Hobby curves need exact coordinates rather than node boundaries that are resolved later. Since your nodes are circles, this doesn't actually cause a problem since we can use the centre of the node to define the curve and then shorten it by a bit more than the radius of the circle.
• Obviously, the position of the coordinate that the path goes through can be customised.
• The options for the edge path should be given via every edge/.style rather than on the path itself since the purpose of the path is just for positioning and isn't intended to construct an actual path (I found this out when a strange arrow head appeared when I was trying things out)

\documentclass{article}
%\url{https://tex.stackexchange.com/q/617538/86}
\usepackage{tikz}

\usetikzlibrary{hobby}

\begin{document}
\begin{tikzpicture}
    \draw[very thick, step = 2] (0, 0) grid (6, 6);

\foreach \x in {0,2,4}
\foreach \y in {0,2,4}
\node[circle, fill=blue] (grid-\x-\y) at (\x,\y) {};

\path (grid-0-0) ++(-1,-1) coordinate (a);

\path[
  every edge/.style={very thick, draw=red,->}
]
        (grid-2-0) edge (grid-0-2)
        (grid-0-2) edge[bend left] (grid-2-2)
        (grid-2-2) edge[bend right] (grid-2-4)
        (grid-2-4) edge (grid-4-0)
        (grid-4-0.center) edge[shorten <=5pt,shorten >=5pt,curve through=(a)] (grid-0-4.center)
        (grid-4-4) edge[bend left] (grid-4-2)
        (grid-4-2) edge (grid-2-0);

\end{tikzpicture}
\end{document}

Answer 3

I use the controls operation to get full controls curvy curves. control works for both coordinate and node. All other operations to, --, to[bend left], ... are special cases of controls.

Some explaination: Imagine we shoot from shooting point (b) with shooting angle -150 and shooting force 2; shoot from shooting point (f) with shooting angle -120 and shooting force 2.

(b) ..controls +(-150:2) and +(-120:2) .. (f)

\documentclass[tikz,border=10mm]{standalone}
\begin{document}
\begin{tikzpicture}[scale=2]
\draw[very thick] (0,0) grid (3,3);
        
\foreach \p/\pname in {(1,0)/a,(2,0)/b,(0,1)/c,(1,1)/d,(2,1)/e,(0,2)/f,(1,2)/g,(2,2)/h} 
\path \p node[circle,fill=blue,text=white] (\pname){};
        
\begin{pgfinterruptboundingbox} % prevent bounding box larger when using `controls`     
\begin{scope}[very thick,red]
\draw[->] (h) to[bend left] (e);
\draw[->] (e) to[bend right] (a);
\draw[->] (a) to[bend left] (c);
\draw[->] (c) to[bend left] (d);
\draw[->] (d) to[bend left] (g);
\draw[->] (g) to (b);
\draw[->] (b) ..controls +(-150:2) and +(-120:2) .. (f);
\end{scope}
\end{pgfinterruptboundingbox}
\end{tikzpicture}
\end{document}