TikZ: Curved line bending the wrong way

Question

I am trying to draw a schematic with TikZ, and I need to have a curved line in it.

I know the basics, the problem is that the line should be curved on the left, while it is always curved on the right. Has anyone any idea of why it is happening this way.

Here is my environment:

\documentclass[aspectratio=169, 14pt, notes]{beamer}
\usetheme{Madrid}
\usepackage{tikz}
\usetikzlibrary{arrows.meta, calc, datavisualization.formats.functions, fadings, fit, graphs, intersections, math, patterns, positioning, shapes, shadows, through, tikzmark}
\begin{document}
  \begin{frame}
    \frametitle{My frame title}
    \framesubtitle{My frame subtitle}
    \begin{tikzpicture}[remember picture, overlay]
      \node[inner sep=0pt, anchor=center, opacity=0.15, draw=blue5, font=\small, fit={({$(current page.north)!0.38!(current page.south)$} -| {$(current page.west)!0.08!(current page.east)$}) ({$(current page.north)!0.82!(current page.south)$} -| {$(current page.west)!0.92!(current page.east)$})}] (Wiring) at (current page.center) {This is my first box};
      \draw[stealth-, dashed, line width=0.25mm, draw=green5] ($(Wiring.north west)!0.10!(Wiring.south west)$) to[out=180, in=180] ({$(Wiring.north)!-0.15!(Wiring.south)$} -| {$(Wiring.west)!0.05!(Wiring.east)$});
    \end{tikzpicture}
  \end{frame}
\end{document}

And here is a capture of what I get:

Here you I have added a violet line with what I want Thanks for the help,

Answer 1

Whether this is a bug or not, I can't tell at the moment, but obviously, you can't mix the -| syntax and the $...$ syntax provided by the calc library with the bending options of a to path. You can't mix the -| syntax and the $...$ syntax at all, I would assume.

However, you can define two coordinates using the $...$ sytnax and then use these with the -| syntax:

\documentclass[aspectratio=169, 14pt, notes]{beamer}
\usetheme{Madrid}
\usepackage{tikz}
\usetikzlibrary{calc, fit}
\usepackage{ninecolors}
\begin{document}
  \begin{frame}
    \frametitle{My frame title}
    \framesubtitle{My frame subtitle}
    \begin{tikzpicture}[remember picture, overlay]
      \node[inner sep=0pt, anchor=center, opacity=0.15, draw=blue5, font=\small, fit={({$(current page.north)!0.38!(current page.south)$} -| {$(current page.west)!0.08!(current page.east)$}) ({$(current page.north)!0.82!(current page.south)$} -| {$(current page.west)!0.92!(current page.east)$})}] (Wiring) at (current page.center) {This is my first box};
      \coordinate (A) at ($(Wiring.north)!-0.15!(Wiring.south)$); 
      \coordinate (B) at ($(Wiring.west)!0.05!(Wiring.east)$); 
      \draw[stealth-, dashed, line width=0.25mm, draw=green5] ($(Wiring.north west)!0.10!(Wiring.south west)$) to[out=180, in=180] (A -| B);
    \end{tikzpicture}
  \end{frame}
\end{document}

Alternatively, since the problem more or less only affects the in option, you could use other ways to bend the path such as bend left or add relative as option (as in to[out=90, in=90, relative]).

---

I haven't found the reason for this behaviour yet, but a minimal working example to reproduce the problem is:

\documentclass[border=10pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}
    \begin{tikzpicture}
        \draw[->] (0,0) to[out=180, in=180] ({$(0,10)!0.5!(0,-5)$} -| {$(-10,0)!0.5!(5,0)$});
        \draw[->, red] (0,0) to[out=180, in=180] (0,2.5 -| -2.5,0);
    \end{tikzpicture}
\end{document}

The expected output would be that the path describes a curve that is bent to the left only (so that it enters the target node from the left) as shown in red, but it does not:

Answer 2

Not to be confused with the node cs:.

We'll setup the xyz coordinate system so that the values [0, 1] cover the (hopefully) rectangular node from left to right (x) and bottom to top (y)

1. Shift the coordinate system to the south west corner of the node.
2. The x and y key are used so that the x vector goes (from the new origin) to the south east corner and the y vector goes to the north west corner.
3. We ignore z.

Since the default direction of the y vector is upwards, I'll also set this up in this solution. The values needs to be swapped in relation to your approach (downwards). You can see this in the code since all y values are subtracted from 1.

Code

\documentclass[aspectratio=169, 14pt, notes]{beamer}
\usetheme{Madrid}
\usepackage{tikz}
\usetikzlibrary{arrows.meta, fit}
\tikzset{
  node cs/.default=current page,
  node cs/.style={%
    shift={(#1.south west)},
    x={(#1.south east)},
    y={(#1.north west)}}}
\begin{document}
\begin{frame}
\frametitle{My frame title}
\framesubtitle{My frame subtitle}
\begin{tikzpicture}[remember picture, overlay]
\path[node cs] node[inner sep=0pt, anchor=center, opacity=0.15, draw=blue, font=\small, 
  fit={(0.08, 1-0.38)(0.92, 1-0.82)}] (Wiring) at (current page.center) {This is my first box};
\draw[Stealth-, dashed, line width=0.25mm, draw=green, node cs=Wiring]
  (0, 1-0.10) to[out=180, in=180, looseness=2] (0.05, 1+0.15);
\end{tikzpicture}
\end{frame}
\end{document}

Output