How to reduce the width of a composite figure with the command arc and a line in TikZ?

Question

I have this tikzpicture:

\documentclass[10pt]{article}
\usepackage{tikz}

\begin{document}

\begin{tikzpicture}
    \draw[line width=0.5cm] (10cm,1cm)--(12cm,1cm) arc(90:-90:1.3cm and 0.943cm) --(10cm,-0.885cm);
\end{tikzpicture}

\end{document}

Is there any way to get to this?:

That is, the thickness of the arch decreases as it goes down (even if the lower horizontal line has the same thickness as the end of the arch).

Thanks!

score 5 · Accepted Answer · answered Jan 31 '18 at 21:02

5

\documentclass[10pt]{article}
\usepackage{tikz}

\begin{document}

\begin{tikzpicture}
    \draw[fill] (10cm,1cm)--
(12cm,1cm) arc(90:-90:1.3cm and 0.943cm) --
(10cm,-0.885cm) --
(10cm,-1.1cm) --
(12cm,-1.1cm)  arc(-90:90:1.5cm and 1.3cm) --
(10cm, 1.5cm) 
;
\end{tikzpicture}

\end{document}

answered Jan 31 '18 at 21:02

David Carlisle

757,742

Oh, an answer from David!! I thought there was some parameter of the arc command that made the end less thick, but it seems that it is not. I sensed it because I find it hard to see all the parts that make up the figure haha, but I will pay attention. Thanks! – manooooh Jan 31 '18 at 21:10
@manooooh it's possible that you could play with the decorations library to draw each path segment a slightly narrower width, but filling the final outline more likely to give smoother result although you have to draw the outline "by hand" – David Carlisle Jan 31 '18 at 21:12
How can I do the same but with the difference that, looking superiorly, the figure starts with the thin arc, and ends with the thick line, besides enlarging the arc so there is a little more distance between the horizontal lines? (Lengthening the arch creates more distance). I have a mess in my head with so many parts :(. Thanks – manooooh Jan 31 '18 at 22:10
@manooooh I am not sure I understood the comment, for testing , change fill back to line width=0.5mm or something and draw the outline, when you are happy with it change it back to fill – David Carlisle Jan 31 '18 at 22:48
Sometimes I express myself badly... Apologies. Now I realize that I simply want to rotate the figure vertically. I added as parameter rotate=180 to the draw command (\draw[fill,rotate=180]...), but I need that the figure points towards the left side, and not the right, as it does the 180 degrees. – manooooh Jan 31 '18 at 23:12
I answer to myself. I could get adding \reflectbox{...}. – manooooh Feb 01 '18 at 00:08
1

@manooooh why draw it one way then reflect? you could just negate all the x coordinates and draw it in the other direction. – David Carlisle Feb 01 '18 at 07:57

score 1 · Answer 2 · 2018-01-31T23:51:32.877

I could not refrain from resurrecting an old trick by Alain Matthes.

\documentclass{minimal}
\usepackage{tikz}
\usetikzlibrary{decorations}
\begin{document}

\makeatletter
%from https://tex.stackexchange.com/a/14295/121799
\pgfkeys{/pgf/decoration/.cd,
         start color/.store in =\startcolor,
         end color/.store in   =\endcolor,
         vertical decrease slope/.store in = \DrasticY,
         color slope/.store in = \ColorSensitivity
}

\pgfdeclaredecoration{vertical width and color change}{initial}{
 \state{initial}[width=0pt, next state=line, persistent precomputation={%
   \pgfmathdivide{50}{\pgfdecoratedpathlength}%
   \let\increment=\pgfmathresult%
   \pgfmathsetmacro{\orilinewidth}{\pgflinewidth}%
   \pgfmathsetmacro{\ynod}{\pgf@y}%
   \def\x{0}%
 }]{}
 \state{line}[width=.5pt,   persistent postcomputation={%
     \pgfmathsetmacro{\x}{\the\pgf@y-\ynod}%
   }]{%
   \pgfmathsetmacro{\newlinewidth}{max(\DrasticY*\x*0.075pt+\orilinewidth,0)}%
   \pgfsetlinewidth{\newlinewidth}
   \pgfsetarrows{-}%
   \pgfpathmoveto{\pgfpointorigin}%
   \pgfpathlineto{\pgfqpoint{.75pt}{0pt}}%
    \pgfmathtruncatemacro{\absx}{round(100*(1-min(max(\ColorSensitivity*(\x+28),0),1)))}
   \pgfsetstrokecolor{\endcolor!\absx!\startcolor}%
   \pgfusepath{stroke}%
 }
 \state{final}{%
   \pgfsetlinewidth{\pgflinewidth}%
   \pgfpathmoveto{\pgfpointorigin}%
    \pgfmathtruncatemacro{\absx}{round(100*(1-min(max(\ColorSensitivity*(\x+28),0),1)))}
   \color{\endcolor!\absx!\startcolor}%
   \pgfusepath{stroke}% 
 }
}

\makeatother

\begin{tikzpicture}
  \begin{scope}
    \draw[ line width=0.5cm, decoration={vertical width and color change,   
start color=black, end color=black,vertical decrease slope=0.8,color slope=0.025}, decorate] (10cm,1cm) -- (12cm,1cm) 
     arc(90:-90:1.3cm and 0.943cm) 
    to (10cm,-0.885cm);
 \end{scope}
 \begin{scope}[xshift=5cm]
    \draw[ line width=0.5cm, decoration={vertical width and color change,   
start color=blue, end color=black,vertical decrease slope=3.8,color slope=0.02}, decorate] (10cm,1cm) -- (12cm,1cm) 
     arc(90:-90:1.3cm and 0.943cm) 
    to (10cm,-0.885cm);
 \end{scope}
\end{tikzpicture}
\end{document}

One can control the amount by which the line width decreases by adjusting vertical decrease slope and one may even play with the color.

ooh decorations: https://tex.stackexchange.com/questions/413076/how-to-reduce-the-width-of-a-composite-figure-with-the-command-arc-and-a-line-in/413083?noredirect=1#comment1031412_413083 — David Carlisle, Jan 31 '18 at 23:16

How to reduce the width of a composite figure with the command arc and a line in TikZ?

2 Answers2