Dois vetores têm a mesma direção e suas setas permanecem indiferenciadas. Quero fazê-los aparecer como “gêmeos siameses”, uma metade flecha para a esquerda e outra metade para a direita. O que quero dizer pode ser melhor explicado no canto superior esquerdo da imagem a seguir: (uma seta é vermelha e a outra é preta).
NoManual"TikZ and pgf" do Till Tantau, não encontrei esse estilo. Na verdade, quando tentei usar [o-stealth], obtive o seguinte:
Não conheço a chave 'o'.
Meu código está uma bagunça, mas super simples já que sou novato no Tikz. Aqui vai uma parte:
\documentclass[tikz]{standalone}
\usepackage[utf8]{inputenc}
\usepackage{tikz}\begin{document}
\usetikzlibrary{calc,patterns,angles,quotes}
\begin{tikzpicture}
\pgfmathsetmacro{\Gvec}{1}
\pgfmathsetmacro{\midAngle}{20}
\pgfmathsetmacro{\Gcosmid}{\Gvec*cos(\midAngle)}
\coordinate (center) at (0,0);
\draw [thin, gray] (center) -- ++(270-\midAngle:2) coordinate (left);
\draw [thick, -stealth] (left)-- ++(90-\midAngle:\Gcosmid + 0.3) coordinate (Tmid);
\draw [thin] (left) -- ++(270-\midAngle:-\Gcosmid) coordinate (gcosmid);
\draw [->, red] (gcosmid) -- (Tmid) node [left] {\footnotesize{$a_{cp}$}};
\end{tikzpicture}
Suponho que a "flecha siamesa" seria uma ótima maneira de lidar com o problema. Mas aceito outras alternativas.
Editar: As setas siamesas dependem principalmente da diferenciação de cores. Posteriormente apostei em uma boa combinação de shape (sobreposição dos estilos -stealth e -angle 90, quando os vetores possuem a mesma natureza, ex: mg e a_r).
Responder1
Bem-vindo! Aqui está uma ponta de flecha "Siamese Stealth". Eu não tinha certeza do formato, então usei Stealthcomo base. Você pode copiar os códigos para outros cabeçotes pgflibraryarrows.meta.code.tex, se necessário. Para que isso funcione, é necessário declarar um novo parâmetro de seta, de segunda cor, e dividir os caminhos em dois.
\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{arrows.meta}
\makeatletter
\pgfkeys{/pgf/arrow keys/second color/.code=%
\pgfarrowsaddtooptions{\edef\pgfarrowsecondcolor{#1}}}
\pgfdeclarearrow{
name = Siamese Stealth,
defaults = {
length = +3pt 4.5 .8,
width' = +0pt .75,
inset' = +0pt 0.325,
line width = +0pt 0.5 0.5,
second color=red
},
setup code = {
% Cap the line width at 1/4th distance from inset to tip
\pgf@x\pgfarrowlength
\advance\pgf@x by-\pgfarrowinset
\[email protected]\pgf@x
\ifdim\pgf@x<\pgfarrowlinewidth
\pgfarrowlinewidth\pgf@x
\fi
% Compute front miter length:
\pgfmathdivide@{\pgf@sys@tonumber\pgfarrowlength}{\pgf@sys@tonumber\pgfarrowwidth}%
\let\pgf@temp@quot\pgfmathresult%
\pgf@x\pgfmathresult pt%
\pgf@x\pgfmathresult\pgf@x%
\pgf@x4\pgf@x%
\advance\pgf@x by1pt%
\pgfmathsqrt@{\pgf@sys@tonumber\pgf@x}%
\pgf@xc\pgfmathresult\pgfarrowlinewidth% xc is front miter
\[email protected]\pgf@xc
\pgf@xa\pgf@temp@quot\pgfarrowlinewidth% xa is extra harpoon miter
% Compute back miter length:
\[email protected]\pgfarrowwidth%
\csname pgfmathatan2@\endcsname{\pgfmath@tonumber\pgfarrowlength}{\pgfmath@tonumber\pgf@ya}%
\pgf@yb\pgfmathresult pt%
\csname pgfmathatan2@\endcsname{\pgfmath@tonumber\pgfarrowinset}{\pgfmath@tonumber\pgf@ya}%
\pgf@ya\pgfmathresult pt%
\advance\pgf@yb by-\pgf@ya%
\[email protected]\pgf@yb% half angle in yb
\pgfmathtan@{\pgf@sys@tonumber\pgf@yb}%
\pgfmathreciprocal@{\pgfmathresult}%
\pgf@yc\pgfmathresult\pgfarrowlinewidth%
\[email protected]\pgf@yc%
\advance\pgf@ya by\pgf@yb%
\pgfmathsincos@{\pgf@sys@tonumber\pgf@ya}%
\pgf@ya\pgfmathresulty\pgf@yc% ya is the back miter
\pgf@yb\pgfmathresultx\pgf@yc% yb is the top miter
\ifdim\pgfarrowinset=0pt%
\[email protected]\pgfarrowlinewidth% easy: back miter is half linewidth
\fi
% Compute inset miter length:
\pgfmathdivide@{\pgf@sys@tonumber\pgfarrowinset}{\pgf@sys@tonumber\pgfarrowwidth}%
\let\pgf@temp@quot\pgfmathresult%
\pgf@x\pgfmathresult pt%
\pgf@x\pgfmathresult\pgf@x%
\pgf@x4\pgf@x%
\advance\pgf@x by1pt%
\pgfmathsqrt@{\pgf@sys@tonumber\pgf@x}%
\pgf@yc\pgfmathresult\pgfarrowlinewidth% yc is inset miter
\[email protected]\pgf@yc%
% Inner length (pgfutil@tempdima) is now arrowlength - front miter - back miter
\pgfutil@tempdima\pgfarrowlength%
\advance\pgfutil@tempdima by-\pgf@xc%
\advance\pgfutil@tempdima by-\pgf@ya%
\[email protected]\pgfarrowwidth%
\advance\pgfutil@tempdimb by-\pgf@yb%
% harpoon miter correction
\ifpgfarrowroundjoin
\pgfarrowssetbackend{\pgf@ya\advance\pgf@x by-.5\pgfarrowlinewidth}
\else
\pgfarrowssetbackend{0pt}
\fi
\ifpgfarrowharpoon
\pgfarrowssetlineend{\pgfarrowinset\advance\pgf@x
by\pgf@yc\advance\pgf@x by.5\pgfarrowlinewidth}
\else
\pgfarrowssetlineend{\pgfarrowinset\advance\pgf@x by\pgf@yc\advance\pgf@x by-.25\pgfarrowlinewidth}
\ifpgfarrowreversed
\ifdim\pgfinnerlinewidth>0pt
\pgfarrowssetlineend{\pgfarrowinset}
\else
\pgfarrowssetlineend{\pgfutil@tempdima\advance\pgf@x by\pgf@ya\advance\pgf@x by-.25\pgfarrowlinewidth}
\fi
\fi
\fi
\ifpgfarrowroundjoin
\pgfarrowssettipend{\pgfutil@tempdima\advance\pgf@x by\pgf@ya\advance\pgf@x by.5\pgfarrowlinewidth}
\else
\pgfarrowssettipend{\pgfarrowlength\ifpgfarrowharpoon\advance\pgf@x by\pgf@xa\fi}
\fi
% The hull:
\pgfarrowshullpoint{\pgfarrowlength\ifpgfarrowroundjoin\else\ifpgfarrowharpoon\advance\pgf@x by\pgf@xa\fi\fi}{\ifpgfarrowharpoon-.5\pgfarrowlinewidth\else0pt\fi}%
\pgfarrowsupperhullpoint{0pt}{.5\pgfarrowwidth}%
\pgfarrowshullpoint{\pgfarrowinset}{\ifpgfarrowharpoon-.5\pgfarrowlinewidth\else 0pt\fi}%
% Adjust inset
\pgfarrowssetvisualbackend{\pgfarrowinset}
\advance\pgfarrowinset by\pgf@yc%
% The following are needed in the code:
\pgfarrowssavethe\pgfutil@tempdima
\pgfarrowssavethe\pgfutil@tempdimb
\pgfarrowssavethe\pgfarrowlinewidth
\pgfarrowssavethe\pgf@ya
\pgfarrowssavethe\pgfarrowinset
},
drawing code = {
\pgfsetdash{}{+0pt}%
\ifpgfarrowroundjoin\pgfsetroundjoin\else\pgfsetmiterjoin\fi
\ifdim\pgfarrowlinewidth=\pgflinewidth\else\pgfsetlinewidth{+\pgfarrowlinewidth}\fi
\pgfpathmoveto{\pgfqpoint{\pgfutil@tempdima\advance\pgf@x by\pgf@ya}{-0.5\pgfarrowlinewidth}}%
\pgfpathlineto{\pgfqpoint{\pgf@ya}{-0.5\pgfarrowlinewidth}}%
\pgfpathlineto{\pgfqpoint{\pgfarrowinset}{-0.5\pgfarrowlinewidth}}%
\ifpgfarrowharpoon \else
\pgfpathlineto{\pgfqpoint{\pgf@ya}{-\pgfutil@tempdimb}}%
\fi
\pgfpathclose
\ifpgfarrowopen\pgfusepathqstroke\else\ifdim\pgfarrowlinewidth>0pt\pgfusepathqfillstroke\else\pgfusepathqfill\fi\fi
\pgfsetstrokecolor{\pgfarrowsecondcolor}%
\pgfsetfillcolor{\pgfarrowsecondcolor}%
\pgfpathmoveto{\pgfqpoint{\pgfutil@tempdima\advance\pgf@x by\pgf@ya}{0.5\pgfarrowlinewidth}}%
\pgfpathlineto{\pgfqpoint{\pgf@ya}{0.5\pgfarrowlinewidth}}%
\pgfpathlineto{\pgfqpoint{\pgfarrowinset}{0.5\pgfarrowlinewidth}}%
\ifpgfarrowharpoon \else
\pgfpathlineto{\pgfqpoint{\pgf@ya}{\pgfutil@tempdimb}}%
\fi
\pgfpathclose
\ifpgfarrowopen\pgfusepathqstroke\else\ifdim\pgfarrowlinewidth>0pt\pgfusepathqfillstroke\else\pgfusepathqfill\fi\fi
},
parameters = {
\pgfarrowsecondcolor,%
\the\pgfarrowlinewidth,%
\the\pgfarrowlength,%
\the\pgfarrowwidth,%
\the\pgfarrowinset,%
\ifpgfarrowharpoon h\fi%
\ifpgfarrowopen o\fi%
\ifpgfarrowroundjoin j\fi%
},
}%
\makeatother
\begin{document}
\begin{tikzpicture}
\draw [thick,{Circle[open]}-{Siamese Stealth}] (0,0) -- ++ (70:1);
\draw [thick,{Circle[fill=blue]}-{Siamese Stealth[second color=blue,length=10pt]}] (1,0) -- ++ (70:1);
\draw [thick,{Circle[fill=orange]}-{Siamese Stealth[orange,second color=black,width=6pt]}] (2,0) -- ++ (70:1);
\end{tikzpicture}
\end{document}
Quanto à oponta da seta: ela está definida na arrowsbiblioteca, mas foi substituída por arrows.meta, que é usada aqui. A Circleponta da seta é uma variante mais flexível do o.
Outra possibilidade é usar um arquivo pic. Este possui um código abreviado sem comandos principais pgf, mas também é menos flexível.
\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{arrows.meta}
\begin{document}
\begin{tikzpicture}[pics/Siamese arrow/.style={code={
\tikzset{Siamese arrow/.cd,#1}
\def\pv##1{\pgfkeysvalueof{/tikz/Siamese arrow/##1}}%
\begin{scope}
\clip (-\pv{length}-5pt,0) -- (2pt,0) --
(2pt,0.5*\pv{width}+\pgflinewidth)
-- (-\pv{length}-5pt,0.5*\pv{width}+\pgflinewidth) -- cycle;
\draw[-{\pv{head}[length=\pv{length},width=\pv{width}]},
color=\pv{color 1}] (-\pv{length}+2pt,0) -- (2pt,0);
\end{scope}
\begin{scope}
\clip (-\pv{length}-5pt,0) -- (2pt,0) --
(2pt,-0.5*\pv{width}-\pgflinewidth)
-- (-\pv{length}-5pt,-0.5*\pv{width}-\pgflinewidth) -- cycle;
\draw[-{\pv{head}[length=\pv{length},width=\pv{width}]},
color=\pv{color 2}] (-\pv{length}+2pt,0) -- (2pt,0);
\end{scope}
}},Siamese arrow/.cd,length/.initial=6pt,width/.initial=3pt,
head/.initial=Stealth,color 1/.initial=black,color 2/.initial=red]
%
\draw [thick,shorten >=2pt,{Circle[open]}-] (0,0) -- ++ (70:1)
pic[pos=1,sloped]{Siamese arrow} ;
\draw [thick,shorten >=2pt,{Circle[open]}-] (1,0) -- ++ (70:1)
pic[pos=1,sloped]{Siamese arrow={width=5pt,color 1=blue,color 2=orange}} ;
\draw [thick,shorten >=2pt,{Circle[open]}-] (2,0) -- ++ (70:1)
pic[pos=1,sloped]{Siamese arrow={head=Latex,length=4pt,color 1=red,color 2=blue}} ;
\end{tikzpicture}
\end{document}
