# Tikz: Curved Label for arc

I'm trying to reproduce the following picture with tikz:

And i have my Problems with the curved Label Text 'x-f(x)'

My code looks like this:

\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\coordinate (M) at (0,0);
\coordinate (A) at (0,3);
\coordinate (C) at (135:3);
\begin{scope}
\draw [step=3,very thin,gray](-3,-3) grid (3,3);
\end{scope}
\draw (A) node[circle,inner sep=1.5pt,fill] {} (C) node[circle,inner sep=1.5pt,fill] {} (M) node[circle,inner sep=1.5pt,fill] {};
\draw[-] (M) -- (C) (M) -- (A);
\draw[dotted,|-|]
(0,3cm+10pt)
node[midway,fill=white] {\tiny{$x-f(x)$}};
\end{tikzpicture}
\end{document}


I found the 'decorations' Package but could not get it to work like in the picture. I would really appreciate help. Thanks in advance.

Just add the sloped option (see p 237 of the manual)

\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\coordinate (M) at (0,0);
\coordinate (A) at (0,3);
\coordinate (C) at (135:3);
\begin{scope}
\draw [step=3,very thin,gray](-3,-3) grid (3,3);
\end{scope}
\draw (A) node[circle,inner sep=1.5pt,fill] {} (C) node[circle,inner sep=1.5pt,fill] {} (M) node[circle,inner sep=1.5pt,fill] {};
\draw[-] (M) -- (C) (M) -- (A);
\draw[dotted,|-|]
(0,3cm+10pt)
node[midway,fill=white,sloped] {\tiny{$x-f(x)$}};
\end{tikzpicture}
\end{document}


If you want to bend the text according to the path, you have to use the decorations libraries.

Unfortunately it doesn't work when maths are involved. See this answer and the pgf documentation.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{
decorations.markings,
decorations.pathmorphing,
decorations.text,
}
\begin{document}
\begin{tikzpicture}
\coordinate (M) at (0,0);
\coordinate (A) at (0,3);
\coordinate (C) at (135:3);
\begin{scope}
\draw [step=3,very thin,gray](-3,-3) grid (3,3);
\end{scope}
\draw (A) node[circle,inner sep=1.5pt,fill] {} (C) node[circle,inner sep=1.5pt,fill] {} (M) node[circle,inner sep=1.5pt,fill] {};
\draw[-] (M) -- (C) (M) -- (A);
\draw [dotted,|-|, postaction={decorate, decoration={text align={center},raise={1mm},text along path, text={|\tiny\color{blue}|{$x-f(x)+36\ln\cos x$}}}}] (135:3cm+10pt) arc (135:90:3cm+10pt);
\draw [dotted,|-|, postaction={decorate, decoration={text align={center},raise={1mm},text along path, text={|\tiny\color{red}|Some long text}}}] (135:3cm+10pt) arc (135:90:3cm+10pt);
\end{tikzpicture}
\end{document}


Just for fun, and because you developed your MWE, here is a code that is as similar as I can make to the example you gave.

@AndréC, option with basic tikz code for nodes in a path, is the most simple with the option sloped, but if the text is long, the second option from @NBur is a good option but has some issues when the text is in math mode, specifically to place a white outline that cuts the dotted lines, I cant find a solution with text effects along path that could draw a background box for each character, but for that reason I think is not compatible with math mode; another option is with contour but I could not merge it inside text along path decoration in math mode, at the end I decided to put a decorations.markings, and draw a node in the middle, same effect as the basic code, but all in white to not lost the text along path in math mode...

RESULT:

MWE:

\documentclass[tikz]{standalone}
\usepackage[scaled]{helvet}
\usetikzlibrary{backgrounds,arrows.meta,decorations.text,decorations.markings,calc}
\definecolor{myRed}{HTML}{C2504B}
\definecolor{myGreen}{HTML}{769144}
\definecolor{myBlue}{HTML}{375C8C}
\definecolor{myColor1}{HTML}{AABFC8}

\begin{document}
\begin{tikzpicture}[
%Environment Config
font=\sffamily,
%Environment Styles
ThickNode/.style={
circle,
draw=black,
line width=5pt,
inner sep=2pt,
},
HugeLine/.style={
line width=4pt,
shorten >=-4pt,
shorten <=-4pt,
preaction={
transform canvas={
shift={(2pt,-1pt)}
},
draw=gray,
draw opacity=0.4,
very thick
}
},
HugeArrow/.style={
>={Straight Barb[line cap=round,length=7pt]},
line width=4pt,
shorten >=4pt,
shorten <=-4pt,
preaction={
transform canvas={
shift={(1pt,-2pt)}
},
draw=gray,
draw opacity=0.3,
line width=3pt,
},
preaction={
transform canvas={
shift={(1pt,-2pt)}
},
draw=gray,
draw opacity=0.2,
line width=5pt,
}
},
Dim/.style={
draw,
>={Turned Square[length=5pt]},
shorten >=0pt,
shorten <=0pt,
<->,
densely dotted,
line width=0.75pt,
preaction={
transform canvas={
shift={(1pt,-1pt)}
},
draw=gray,
draw opacity=0.3,
very thick
},
preaction={
transform canvas={
shift={(1pt,-1pt)}
},
draw=gray,
draw opacity=0.1,
line width=3pt,
},
postaction={
decoration={
markings,
mark= at position .5 with {
\node[fill=white,text=white,transform shape]{#1};
}
},
decorate
},
postaction={
decoration={
text along path,
raise=-2pt,
text={||#1{}},
text align=center,
reverse path
},
decorate
}
},
]
\def\PolarA{90}
\def\PolarB{-40}
\def\PolarE{160}
\draw
(0,0) node[ThickNode,label={[inner sep=1pt]5:O}](O){}
\begin{scope}[on background layer]
\draw[draw=myColor1]
(0,0)
\draw[myBlue,ultra thick]
%Draw Red section
\draw[HugeArrow,myRed,->]
\draw[Dim,myRed]
arc (\PolarA:\PolarB:\Rad+0.5cm) node[midway,circle,fill=white]{$x$};

%Draw Green section
\draw[HugeArrow,myGreen,->]
-- (B.center);
\draw[Dim=$x-f(x)$,myGreen]
\coordinate (B') at ($(B.center)!.5cm!90:(E.center)$);
\coordinate (E') at ($(E.center)!-.5cm!90:(B.center)$);
\draw[Dim=$f(x)$,myGreen]
(B')
-- (E');
%Draw A-O
\draw[HugeLine,myGreen]
(O.90+25)
-- (A.-90-25);
\draw[HugeLine,myRed]
(O.90-25)
-- (A.-90+25);
\end{scope}
\end{tikzpicture}
\end{document}


## Clarifications

The dotted line for the dimension from the line EB, uses calc library code to find the points E' a B' that are distance points relative from a path in the case of B' is the point from vector BE rotated 90 degrees dimensioned to the distance, this case 0.5cm, for the E' point the rotated angle should be -90 degrees, but is the same if the distance is negative, see PGF-Manual 13.5.4 The Syntax of Distance Modifiers; these points define a line with the same dimension separated 0.5 cm, the problem is visual, as the image shows the turned square terminations center is not in the end of the path, but you could modify it locally in the \draw[options] line using shorten > and shorten < properties.

Testing drawings:

Add the code lines below scope:

    .
.
.
\end{scope}

%testing lines
\coordinate (B'') at ($(B.center)!1.5cm!90:(E.center)$);
\coordinate (B*) at ($(B.center)!-1.5cm!90:(E.center)$);
\draw(B) -- (B'') node[fill,circle,inner sep=1pt,label={-90:\scriptsize B''}]{};
\draw[blue](B) -- (B*) node[fill,circle,inner sep=1pt,label={[inner sep=1pt]-45:\scriptsize B*}]{};
\coordinate (E'') at ($(E.center)!-1.5cm!90:(B.center)$);
\coordinate (E*) at ($(E.center)!1.5cm!90:(B.center)$);
\draw(E) -- (E'') node[fill,circle,inner sep=1pt,label={-90:\scriptsize E''}]{};
\draw[blue](E) -- (E*) node[fill,circle,inner sep=1pt,label={[inner sep=1pt]-45:\scriptsize E*}]{};

\coordinate (B''') at ($(B.center)!1cm!90:(E.center)$);
\coordinate (E''') at ($(E.center)!-1cm!90:(B.center)$);
(B''')
-- (E''');
\draw[font=\tiny,inner sep=1pt]
(E*) -- ++ (5pt,5pt) node[anchor=180,fill=yellow]{\verb+$(E.center)!1.5cm!90:(B.center)$+}
(E'') -- ++ (5pt,5pt) node[anchor=180,fill=yellow]{\verb+$(E.center)!-1.5cm!90:(B.center)$+}
(B*) -- ++ (-5pt,5pt) node[anchor=0,fill=yellow]{\verb+$(B.center)!-1.5cm!90:(E.center)$+}
(B'') -- ++ (-5pt,5pt) node[anchor=0,fill=yellow]{\verb+$(B.center)!1.5cm!90:(E.center)$+};

\end{tikzpicture}
\end{document}

• It's really beautiful, bravo! – AndréC Aug 23 '18 at 20:47
• Really nice of you, much appreciated! One Question tho, I dont understand the Part  \coordinate (B') at ($(B.center)!.5cm!90:(E.center)$); \coordinate (E') at ($(E.center)!-.5cm!90:(B.center)$); I would like the dotted line with the label f(x) to be as long as the green line above, so the vertices of the dotted line should be angled 90° to the green line. With the code it looks a little odd and not exactly as long. I don't understand why you need to use 0.5 and -0.5 and not twice -0.5. – RobEva Aug 24 '18 at 13:16
• @RobEva , look at the clarification that I have updated. – J Leon V. Aug 24 '18 at 17:24