I wish to draw a curved arrow whose thickness changes from end to head. Such arrows are commonly used in military maps to denote the moves of forces. Below is an example.
Is it possible to do it in tikz? Thanks!
4
- 1Although typically questions like this will get a lot of comments about "showing what you've tried", in this case, the problem is truly quite difficult with TikZ. Related: Stroke with variable thickness and possibly Is it possible to increase the line's width from its start to its end?Alan Munn– Alan Munn2017-10-24 04:02:13 +00:00Commented Oct 24, 2017 at 4:02
- 1OTOH, if you don't think of it as an arrow, but as two curved lines with a straight line at one end and a triangle at the other...John Kormylo– John Kormylo2017-10-24 04:11:11 +00:00Commented Oct 24, 2017 at 4:11
- @JohnKormylo Yes, that's probably the simplest way to draw them, but still not totally straightforward.Alan Munn– Alan Munn2017-10-24 04:15:32 +00:00Commented Oct 24, 2017 at 4:15
- @AlanMunn - The question is how to parameterize the arrow. End points aren't enough, you need the starting width, ending width and curvature.John Kormylo– John Kormylo2017-10-24 04:19:41 +00:00Commented Oct 24, 2017 at 4:19
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1 Answer
Not amazing, and will quite happily produce horrendous results with extreme curves or parameter values. Currently for single curveto operations only (i.e., paths consisting of a single Bézier curve).
\documentclass[tikz,margin=5]{standalone} \usetikzlibrary{calc,decorations.pathreplacing,decorations.markings} \tikzset{big arrow/.style={ /tikz/big arrow/.cd, #1, /tikz/.cd, decoration={show path construction, curveto code={% % \path [discard, decoration={ markings, mark=at position -\bigarrowlength with {\coordinate (@); }}, decorate] (\tikzinputsegmentfirst) .. controls (\tikzinputsegmentsupporta) and (\tikzinputsegmentsupportb) .. (\tikzinputsegmentlast); \path[big arrow/.cd,#1] let \p1=(\tikzinputsegmentfirst), \p2=(\tikzinputsegmentsupporta), \p3=(\tikzinputsegmentsupportb), \p4=(@), \p5=(\tikzinputsegmentlast), \n1={atan2(\y2-\y1,\x2-\x1)}, \n2={atan2(\y4-\y3,\x4-\x3)} in (\p1) -- ++(\n1+90:\bigarrowstartwidth/2) .. controls ++(\x2-\x1, \y2-\y1) and ++(\x3-\x4, \y3-\y4) .. ($(\p4)+(\n2+90:\bigarrowendwidth/2)$) -- ($(\p4)+(\n2+90:\bigarrowwidth/2)$) -- (\p5) -- ($(\p4)+(\n2-90:\bigarrowwidth/2)$) -- ($(\p4)+(\n2-90:\bigarrowendwidth/2)$) .. controls ++(\x3-\x4, \y3-\y4) and ++(\x2-\x1, \y2-\y1) .. ($(\p1)+(\n1-90:\bigarrowstartwidth/2)$) -- cycle; % }}, decorate }, big arrow/.cd, start width/.store in=\bigarrowstartwidth, end width/.store in=\bigarrowendwidth, length/.store in=\bigarrowlength, width/.store in=\bigarrowwidth, start width=1cm, end width=0.5cm, length=0.25cm, width=1cm, .unknown/.code=% {\let\searchname=\pgfkeyscurrentname\pgfkeysalso{/tikz/\searchname=#1}}% } \begin{document} \begin{tikzpicture} \draw [big arrow={fill=red}] (0,0) to [bend left] (5,5); \draw [big arrow={fill=green, length=0.5cm}] (0,0) to [bend right] (-3,3); \draw [big arrow={fill=blue, start width=1.5cm, end width=1cm, width=1.5cm, length=0.75cm}] (0,0) to [bend right] (4,0); \end{tikzpicture} \end{document} 
