Change the distance dimension of a line as a decoration in TikZ

Question

How I can change the distance dimension like the picture below. In the \dim={add dim, distance} have two parameter I want to add 1 parameter for distance of dimesion like picture 1 , and rolate the text in picture 2.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{decorations,decorations.markings,decorations.text}

\begin{document}
 \pgfkeys{/pgf/decoration/.cd,
      distance/.initial=10pt, 
      distance2/ .initial=10pt
}  

\pgfdeclaredecoration{add dim}{final}{
\state{final}{% 
\pgfmathsetmacro{\dist}{45pt*\pgfkeysvalueof{/pgf/decoration/distance}
            /abs(\pgfkeysvalueof{/pgf/decoration/distance})}    
          \pgfpathmoveto{\pgfpoint{0pt}{0pt}}             
          \pgfpathlineto{\pgfpoint{0pt}{\dist}}   
          \pgfpathmoveto{\pgfpoint{\pgfdecoratedpathlength}{0pt}} 
          \pgfpathlineto{\pgfpoint{(\pgfdecoratedpathlength}{\dist}}     
          \pgfsetarrowsstart{latex}
          \pgfsetarrowsend{latex}
          \pgfpathmoveto{\pgfpoint{0pt}{\dist}}
          \pgfpathlineto{\pgfpoint{\pgfdecoratedpathlength}{\dist}} 
          \pgfusepath{stroke} 
          \pgfpathmoveto{\pgfpoint{0pt}{0pt}}
          \pgfpathlineto{\pgfpoint{\pgfdecoratedpathlength}{0pt}}
}}

\tikzset{dim/.style args={#1,#2,#3}{decoration={add dim,distance=#2},
                decorate,
                postaction={decorate,decoration={text along path,
                                                 raise=#2,
                                                 text align={align=center},
                                                 text={#1}}}}}

\begin{tikzpicture}
\coordinate (A) at (0,0);
\coordinate (B) at (4,2);

\draw[dim={35 cm,34pt,34pt}]  (A) --  (B); 

\draw[fill=gray] (A) circle(2pt); 
\draw[fill=gray] (B) circle(2pt);

\end{tikzpicture}

\end{document}

Answer 1

You need to transform a little your code. The distance is given by the second parameter #2

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{decorations,decorations.markings,decorations.text}

\begin{document}
\pgfkeys{/pgf/decoration/.cd, distance/.initial = 10pt}  

\pgfdeclaredecoration{add dim}{final}{
\state{final}{% 
\pgfmathsetmacro{\dist}{\pgfkeysvalueof{/pgf/decoration/distance}}
          \pgfpathmoveto{\pgfpoint{0pt}{0pt}}             
          \pgfpathlineto{\pgfpoint{0pt}{1.2*\dist}}   
          \pgfpathmoveto{\pgfpoint{\pgfdecoratedpathlength}{0pt}} 
          \pgfpathlineto{\pgfpoint{(\pgfdecoratedpathlength}{1.2*\dist}}     
          \pgfsetarrowsstart{latex}
          \pgfsetarrowsend{latex}
          \pgfpathmoveto{\pgfpoint{0pt}{\dist}}
          \pgfpathlineto{\pgfpoint{\pgfdecoratedpathlength}{\dist}} 
          \pgfusepath{stroke} 
          \pgfpathmoveto{\pgfpoint{0pt}{0pt}}
          \pgfpathlineto{\pgfpoint{\pgfdecoratedpathlength}{0pt}}
}}

\tikzset{
    dim/.style args={#1,#2,#3}{%
                decoration = {add dim,distance=\ifx&#2&0pt\else#2\fi},
                decorate,
                postaction = {%
                   decorate,
                   decoration={%
                        raise=#2,
                        markings,
                        mark=at position .5 with {%
                        \node[inner sep=0pt,
                              font=\footnotesize,
                              fill=white,
                              #3] at (0,0) {#1};}
                   }
                }
    },
    dim/.default={,0pt,}
}

\begin{tikzpicture}
\coordinate (A) at (0,0);
\coordinate (B) at (4,2);

\draw[dim={35 cm,10pt,}]  (A) --  (B); 

\draw[fill=gray] (A) circle(2pt); 
\draw[fill=gray] (B) circle(2pt);

\end{tikzpicture}

\begin{tikzpicture}
\coordinate (A) at (0,0);
\coordinate (B) at (4,2);

\draw[dim={35 cm,20pt,transform shape}]  (A) --  (B); 

\draw[fill=gray] (A) circle(2pt); 
\draw[fill=gray] (B) circle(2pt);

\end{tikzpicture}
\end{document}