Tikz vertical lines next to variable text

Question

I'm editing the caption of the Figure environment in a document using Tikz, but I don't know how to make the caption (variable width) to be next to two lines, something like this

I guess the Figure 1 part can be rotating a rectangle, but the caption text is more complicated since I don't know how to draw a single side, and also an extra line with the same height.

I'm also using this post I made before: Modify Figure environment

Answer 1

Something like this? I'm not entirely sure how you envisage this working but I'd recommend using the facilities of caption rather than trying to create your own stuff from scratch, given that you are loading caption already.

\documentclass{article}
\usepackage{caption,array}
\usepackage{lipsum}
\usepackage{tikz}
\usetikzlibrary{positioning}

\DeclareCaptionFormat{sidewise}{%
  \begin{tikzpicture}
    \node (caption text) [align=left] {%
      \begin{tabular}{p{60mm}}
        #3
      \end{tabular}};
    \node (caption label) [rotate=90, inner xsep=0pt, left=5mm of caption text.north west, font=\sffamily] {#1};
    \draw [ultra thick] (caption label.south west) -- (caption label.south east);
    \draw [ultra thick, orange!75!black]  ([xshift=.35em]caption label.south west) -- ([xshift=.35em]caption label.south east);
  \end{tikzpicture}}
\captionsetup{format=sidewise}
\begin{document}
  \lipsum[1]

  \begin{figure}[t!p]
    \centering
    \includegraphics[scale=.5]{example-image-a}
    \caption{My caption can be of a variable size.}
    \label{fig:mylabel}
  \end{figure}%

  \lipsum[2]

  \begin{figure}
    \centering
    \includegraphics[scale=.5]{example-image-b}
    \caption{{This will be a much longer caption. Hence, we need another line.}}
    \label{fig:myotherlabel}
  \end{figure}

\end{document}

EDIT

This is a modification of the version you posted building on my answer above. I wanted to avoid the overfull box warnings that was generating by using an overlay TikZ picture. What I don't understand is why I cannot use a minipage environment of width \textwidth. But it does avoid the warnings, although I'm not sure it is the most efficient method.

Note that you need two runs for things to end up in the right places. On first compilation, things will be (apparently) randomly scattered all over the place.

\documentclass{article}
\usepackage{caption,array}
\usepackage{lipsum}
\usepackage{tikz,tikzpagenodes}

\usetikzlibrary{positioning,tikzmark,calc}

\DeclareCaptionFormat{sidewise}{%
  \raggedleft%
    \begin{tikzpicture}[remember picture]%
      \node (caption text) [align=left] {%
        \begin{minipage}{.975\textwidth}
          #3
        \end{minipage}};
    \end{tikzpicture}%
  \begin{tikzpicture}[overlay, remember picture]
    \node (caption label) [rotate=90, inner xsep=0pt, left=5mm of caption text.north west, font=\sffamily] {#1};
    \draw [ultra thick] (caption label.south west) -- (caption label.south east);
    \draw [ultra thick, orange]  ([xshift=.35em]caption label.south west) -- ([xshift=.35em]caption label.south east);
  \end{tikzpicture}}
\DeclareCaptionLabelSeparator{none}{}
\captionsetup{format=sidewise,justification=justified}

\begin{document}

  \begin{figure}
    \centering
      \includegraphics[scale=.5]{example-image-b}
    \caption{{This will be a much longer caption. Hence, we need another long long long long long long long long long long long long line.}}
    \label{fig:myotherlabel}
  \end{figure}

\lipsum[1]

\end{document}

Answer 2

Using the previous answer, I modified it to get what I was thinking:

\documentclass{article}
\usepackage{caption,array}
\usepackage{lipsum}
%\usepackage{graphicx} <-- TikZ loads this
\usepackage{tikz}

\usetikzlibrary{positioning}

\DeclareCaptionFormat{sidewise}{%
  \hspace{-1.3cm}%
  \begin{tikzpicture}
    \node (caption text) [align=left] {%
      \begin{tabular}{p{\textwidth}}
        #3
      \end{tabular}};
    \node (caption label) [rotate=90, inner xsep=0pt, left=5mm of caption text.north west, font=\sffamily] {#1};
    \draw [ultra thick] (caption text.north west) -- ([yshift=.95em]caption text.south west);
    \draw [ultra thick, orange]  ([xshift=.35em]caption text.north west) -- ([xshift=.35em, yshift=.95em]caption text.south west);
  \end{tikzpicture}}
\captionsetup{format=sidewise}

\begin{document}

  \begin{figure}
    \centering
    \includegraphics[scale=.5]{example-image-b}
    \caption{{This will be a much longer caption. Hence, we need another long long long long long long long long long long long long line.}}
    \label{fig:myotherlabel}
  \end{figure}

\lipsum[1]

\end{document}