Usando \foreach dentro de um comando draw usando TIKZ

Question

Sou novo em usar, \foreachmas não em codificação em geral. Seguindo o código na resposta número 40 deste exemplo:Como desenhar uma linha tangente de um ponto arbitrário em um caminho no TikZ

Como posso condensar adequadamente a tangent=0.xlista na instrução draw?

Eu tentei algumas ideias sem sucesso:

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{decorations.markings}
\begin{document}

\begin{tikzpicture}[
tangent/.style={
    decoration={
        markings,% switch on markings
        mark=
            at position #1
            with
            {
                \coordinate (tangent point-\pgfkeysvalueof{/pgf/decoration/mark info/sequence number}) at (0pt,0pt);
                \coordinate (tangent unit vector-\pgfkeysvalueof{/pgf/decoration/mark info/sequence number}) at (1,0pt);
                \coordinate (tangent orthogonal unit vector-\pgfkeysvalueof{/pgf/decoration/mark info/sequence number}) at (0pt,1);
            }
    },
    postaction=decorate
},
use tangent/.style={
    shift=(tangent point-#1),
    x=(tangent unit vector-#1),
    y=(tangent orthogonal unit vector-#1)
},
use tangent/.default=1
]
\draw [
tangent=0.1,
tangent=0.2,
tangent=0.3,
tangent=0.4,
tangent=0.5,
tangent=0.6,
tangent=0.7,
tangent=0.8,
tangent=0.9,
%%%% attempt 1
%tangent={0.05,0.01,...0.95}
%%%%% attempt 2
%\foreach \y in {0.1,0.2,...,0.9}
%{
%tangent=\y,
%}
] (0,0) arc (180:0:10);

\foreach \x [count=\xi] in {1,1,2,1,2,1,4,3,1.5}
{
\draw [red, thick,->, use tangent=\xi] (0,0) -- (0,-1*\x);
}
\end{tikzpicture}
\end{document}

para obter um resultado como este:

Como posso condensar adequadamente a lista tangent=0.x, na instrução draw?

Answer 1

Quando precisar chamar a mesma tecla repetidamente, você pode usar <key>/.list={<foreach expression>}, onde <foreach expression>pode ser uma lista simples ou uma lista com reticências. Então, neste caso, você pode usar\draw [tangent/.list={0.1,0.2,...,0.9}](0,0) arc (180:0:10);

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{decorations.markings}
\begin{document}

\begin{tikzpicture}[
tangent/.style={
    decoration={
        markings,% switch on markings
        mark=
            at position #1
            with
            {
                \coordinate (tangent point-\pgfkeysvalueof{/pgf/decoration/mark info/sequence number}) at (0pt,0pt);
                \coordinate (tangent unit vector-\pgfkeysvalueof{/pgf/decoration/mark info/sequence number}) at (1,0pt);
                \coordinate (tangent orthogonal unit vector-\pgfkeysvalueof{/pgf/decoration/mark info/sequence number}) at (0pt,1);
            }
    },
    postaction=decorate
},
use tangent/.style={
    shift=(tangent point-#1),
    x=(tangent unit vector-#1),
    y=(tangent orthogonal unit vector-#1)
},
use tangent/.default=1
]
\draw [tangent/.list={0.1,0.2,...,0.9}](0,0) arc (180:0:10);

\foreach \x [count=\xi] in {1,1,2,1,2,1,4,3,1.5}
{
\draw [red, thick,->, use tangent=\xi] (0,0) -- (0,-1*\x);
}
\end{tikzpicture}
\end{document}

Answer 2

Esta é uma abordagem um pouco diferente (admito que é uma solução alternativa), no entanto, funciona perfeitamente neste cenário.

\foreach [count=\y] \x in {1,1,2,1,2,1,4,3,1.5}
{
    \path [tangent=\y/10] (0,0) arc (180:0:10);
    \draw [red, thick, ->, use tangent=1] (0,0) -- (0,-1*\x);
}   
\draw (0,0) arc (180:0:10);

Basta substituir o tikzpicturecorpo por este código.

---

Código final:

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{decorations.markings}

\begin{document}

    \begin{tikzpicture}[
    tangent/.style={
        decoration={
            markings,% switch on markings
            mark=
            at position #1
            with
            {
                \coordinate (tangent point-\pgfkeysvalueof{/pgf/decoration/mark info/sequence number}) at (0pt,0pt);
                \coordinate (tangent unit vector-\pgfkeysvalueof{/pgf/decoration/mark info/sequence number}) at (1,0pt);
                \coordinate (tangent orthogonal unit vector-\pgfkeysvalueof{/pgf/decoration/mark info/sequence number}) at (0pt,1);
            }
        },
        postaction=decorate
    },
    use tangent/.style={
        shift=(tangent point-#1),
        x=(tangent unit vector-#1),
        y=(tangent orthogonal unit vector-#1)
    },
    use tangent/.default=1
    ]

    \foreach [count=\y] \x in {1,1,2,1,2,1,4,3,1.5}
    {
        \path [tangent=\y/10] (0,0) arc (180:0:10);
        \draw [red, thick,->, use tangent=1] (0,0) -- (0,-1*\x);
    }   
    \draw (0,0) arc (180:0:10); 

    \end{tikzpicture}
\end{document}

Answer 3

Isso pode ser feito facilmente com foreach. Eu uso uma abordagem mais simples que a sua. O resultado é

\documentclass[border={10}]{standalone}
\usepackage{tikz}  

\begin{document}

\def \r {8}

\begin{tikzpicture}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\draw[very thick] (\r,0) arc (0:180:\r);

\foreach \angle / \y in {18/6, 36/7, 54/6, 72/7,90/6, 108/7,126/6,144/7,162/6}
\draw [<-, very thick,red]
   ( {  (\y)*cos(\angle)}, { (\y)*sin(\angle)} ) --
   ( {  (\r)*cos(\angle)}, { (\r)*sin(\angle)} );
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\end{tikzpicture}

\end{document}