Tikz \draw with controls with limited range

Question

How can I limit the drawing of a curve defined with \draw .. controls .. to a specific range?

Example: \draw is defined up till x=9, but I would like to stop the \draw for x>=8

 \draw[->] 
  (3,1) .. controls (3.75,1.4) and (4.25,1.4) ..
  (5,1) .. controls (5.75,0.6) and (6.25,0.6) ..
  (7,1) .. controls (7.75,1.4) and (8.25,1.4) ..
  (9,1);

Welcome to TeX.SX! Please help us help you and add a minimal working example (MWE) that illustrates your problem. Reproducing the problem and finding out what the issue is will be much easier when we see compilable code, starting with \documentclass{...} and ending with \end{document}. — dexteritas, Sep 13 '22 at 09:03
You'd probably need to clip it. Unlike metapost I don't think you can get sub paths out of a tikz path. — daleif, Sep 13 '22 at 09:28
Besides clipping, you could shorten the curve or even use a decoration for that. (There's also \pgfpathcurvebetweentime on the lower level.) But I think the easiest following your instruction (x≥8) would be the \clip. — Qrrbrbirlbel, Sep 13 '22 at 10:23
Your drawing looks like a sine curve. There might be a better option drawing this with sin and cos path operations. — Qrrbrbirlbel, Sep 13 '22 at 11:01
Thx @Qrrbrbirlbel . Indeed very similar to sin and cos, and only minor difference. Will yield simpler solution. Thanks for showing the "shorten" feature. New to me. — FiLou, Sep 13 '22 at 12:26

Qrrbrbirlbel · Answer 1 · 2022-09-13T11:30:07.037

In your simple case – because you want to stop the curve exactly at half the length and time – you could use the PGF level command \pgfpathcurvebetweentime which has no proper TikZ path operation.

Instead of

(7,1) .. controls (7.75,1.4) and (8.25,1.4) .. (9,1)

you need to write

(7,1) to[shorten controls={0 .. (7.75,1.4) and (8.25,1.4) .. .5}] (9,1)

where the curve is only drawn between times 0 and 1 - .5. (If both are 0 everything of the curve will be drawn.)

You can't place nodes along that path (but I believe that can be implemented pretty easily).

For more complex situation, I think the best would be to use the spath3 library.

I've also added a very similar curve with sin and cos which doesn't give the exact same curve but might be good enough in your case.

Code

\documentclass[tikz]{standalone}
\makeatletter
\tikzset{
  shorten controls/.code args={#1..#2..#3}{
    \pgfutil@in@{and}{#2}%
    \ifpgfutil@in@\expandafter\pgfutil@firstoftwo
      \else\expandafter\pgfutil@secondoftwo\fi
    {\pgfkeysvalueof{/tikz/@shorten controls/.@cmd}#1..#2..#3\pgfeov}
    {\pgfkeysvalueof{/tikz/@shorten controls/.@cmd}#1..#2and#2..#3\pgfeov}%
  },
  @shorten controls/.style args={#1..#2and#3..#4}{
    to path={
      \pgfextra
        \pgfpathcurvebetweentime{#1}{1-(#4)}
          {\tikz@scan@one@point\pgfutil@firstofone(\tikztostart)}
          {\tikz@scan@one@point\pgfutil@firstofone#2}
          {\tikz@scan@one@point\pgfutil@firstofone#3}
          {\tikz@scan@one@point\pgfutil@firstofone(\tikztotarget)}%
      \endpgfextra
    }
  }
}
\makeatother
\begin{document}
\begin{tikzpicture}[dashed]
\draw[->, red, dash phase=3pt] 
  (3,1) .. controls (3.75,1.4) and (4.25,1.4) ..
  (5,1) .. controls (5.75,0.6) and (6.25,0.6) ..
  (7,1) to[shorten controls={0 .. (7.75,1.4) and (8.25,1.4) .. .5}]
  (9,1);
\draw[->, blue] 
  (3,1) sin ++(1,.3) cos ++(1,-.3) sin ++(1,-.3) cos ++(1,.3) sin ++(1,.3);
\end{tikzpicture}
\tikz\draw[->] 
  (3,1) .. controls (3.75,1.4) and (4.25,1.4) ..
  (5,1) .. controls (5.75,0.6) and (6.25,0.6) ..
  (7,1) to[shorten controls={0 .. (7.75,1.4) and (8.25,1.4) .. .5}]
  (9,1);
\tikz\draw[->] 
  (3,1) sin ++(1,.3) cos ++(1,-.3) sin ++(1,-.3) cos ++(1,.3) sin ++(1,.3);
\end{document}

Output

There's also \tikz\draw[->] plot[smooth, domain=0:10] (\x/2+3, 1+.3*sin(\x*45); but that's a bit too much. — Qrrbrbirlbel, Sep 13 '22 at 11:42
@Qrrbrbirblbel thx. Really like your last solution. Small correction. Should be \draw[->] plot[smooth, domain=0:10] ({\x/2+3}, {1+0.4*sin(\x*45)}) — FiLou, Sep 13 '22 at 18:33

Tikz \draw with controls with limited range

1 Answers1

Code

Output

Linked