Issue with fade-no-fill.sty

Question

I’m trying to have colour gradient on path, and discovered fade-no-fill.sty, which latest version seems to be https://tex.stackexchange.com/a/567029/56823. It works pretty well, but I have two small issues.

My MWE is as follow:

\documentclass[tikz]{standalone}
\usepackage{fade-no-fill}
\usetikzlibrary{shapes}
\begin{document}
\begin{tikzpicture}
    \pgfmathsetmacro{\l}{3}
    \node [red,draw,thick,ellipse] (S) at (-\l,0) {Solide};
    \node [blue,draw,thick,ellipse] (L) at (\l,0) {Liquide};
    \node [green,draw,thick,ellipse] (G) at (0,{\l*sqrt(3)}) {Gaz};
    \path [fade path but don't fill={thick,->,>=latex,transparent!0}{bottom color=red,top color=green}] (S) to[bend left] (G);
    \path [fade path but don't fill={thick,->,>=latex,transparent!0}{top color=green,bottom color=blue}] (G) to[bend left] (L);
    \path [fade path but don't fill={thick,->,>=latex,transparent!0}{right color=blue,left color=red}] (L) to[bend left] (S);
    \path [fade path but don't fill={thick,->,>=latex,transparent!0}{left color=red,right color=blue}] (S) to (L);
    \path [fade path but don't fill={thick,->,>=latex,transparent!0}{top color=green,bottom color=blue}] (L) to (G);
    \path [fade path but don't fill={thick,->,>=latex,transparent!0}{bottom color=red,top color=green}] (G) to (S);
\end{tikzpicture}
\end{document}

It produces this: Note:

1. the clipped blue arrow above “Liquide”.
2. the very strange arrow at the left of “Liquide”.

Any idea what could be causing this and how to solve it?

Answer 1

Here is another methode where all the arrows are drawn twice with two different colors path fading from different directions.

\documentclass[tikz, border=1 cm]{standalone}
\usetikzlibrary{shapes, fadings}
\begin{document}
\begin{tikzpicture}
\node[red,draw,thick,ellipse] (S) at (-3,0) {Solide};
\node[blue,draw,thick,ellipse] (L) at (3,0) {Liquide};
\node[green,draw,thick,ellipse] (G) at (0,{3*sqrt(3)}) {Gaz};
\draw[green, path fading=south, thick ,-latex] (S) to[bend left] (G);
\draw[red, path fading=north, thick ,-latex] (S) to[bend left] (G);
\draw[green, path fading=south, thick ,-latex] (G) to[bend left] (L);
\draw[blue, path fading=north, thick ,-latex] (G) to[bend left] (L);
\draw[blue, path fading=west, thick ,-latex] (L) to[bend left] (S);
\draw[red, path fading=east, thick ,-latex] (L) to[bend left] (S);
\draw[blue, path fading=west, thick, shorten >=5pt] (S) to (L); %this arror is problematic
\draw[blue, thick ,-latex] ([xshift=-4pt] L.west) -- (L.west); %seperate arrow head
\draw[red, path fading=east, thick ,-latex] (S) to (L);
\draw[green, path fading=south, thick ,-latex] (L) to (G);
\draw[blue, path fading=north, thick ,-latex] (L) to (G);
\draw[green, path fading=south, thick ,-latex] (G) to (S);
\draw[red, path fading=north, thick ,-latex] (G) to (S);
\end{tikzpicture}
\end{document}

The horizontal blue arrow head gets clipped, but is redrawn. A more universal method is here: https://tex.stackexchange.com/a/597939/8650

Edit:

The double drawing can be made into a style with a postaction here is a start:

\documentclass[tikz, border=1 cm]{standalone}
\usetikzlibrary{fadings, calc}
\begin{document}
\begin{tikzpicture}   
\foreach \a in {0,10,...,360}{
\coordinate (A) at (0,0);
\coordinate (B) at (\a:3);
\draw let \p1=($(B)-(A)$), \n1={atan2(\y1,\x1)} in [green, path fading=west, fading angle = \n1, thick ,-latex, postaction={draw, red, path fading=east, fading angle = \n1, thick ,-latex}]  ([xshift=5pt, yshift=5pt]A) (A) to[bend left] (B);
}
\end{tikzpicture}
\end{document}

Answer 2

> = latex is an arrow tip without bounding box. (This arrow head is defined in pgfcorearrows.code.tex and is available regardless of whether arrows.meta is included.)

With > = Latex, the arrow tip has a bounding box. (This arrow head is defined in arrows.meta with proper bounding box.)

Answer 3

Since we are into workarounds, I’ve tried this one:

\documentclass[tikz]{standalone}
\usepackage{fade-no-fill}
\usetikzlibrary{shapes}
\begin{document}
\begin{tikzpicture}
    \pgfmathsetmacro{\l}{3}
    \node [red,draw,thick,ellipse] (S) at (-\l,0) {Solide};
    \node [blue,draw,thick,ellipse] (L) at (\l,0) {Liquide};
    \node [green,draw,thick,ellipse] (G) at (0,{\l*sqrt(3)}) {Gaz};
    \path [fade path but don't fill={thick,->,>=latex,transparent!0}{bottom color=red,top color=green}] (S) to[bend left] (G);
    \path [fade path but don't fill={thick,->,>=latex,transparent!0}{top color=green,bottom color=blue}] (G) to[bend left] (L);
    \path [fade path but don't fill={thick,->,>=latex,transparent!0}{right color=blue,left color=red}] (L) to[bend left] (S);
    \path [fade path but don't fill={thick,->,>=latex,transparent!0}{left color=red,right color=blue}] (S) to (L);
    \path [fade path but don't fill={thick,->,>=latex,transparent!0}{top color=green,bottom color=blue}] (L) to (G);
    \path [fade path but don't fill={thick,->,>=latex,transparent!0}{bottom color=red,top color=green}] (G) to (S);
    \draw [thick,<-,>=latex,blue] (L.west) -- ++(-0.1,0); % Redraw west arrow
    \draw [thick,<-,>=latex,blue] (L.north) -- ++(0,0.1); % Redraw north arrow
\end{tikzpicture}
\end{document}

The result suits me, but this is still a workaround nonetheless.

Answer 4

I do not know \usepackage{fade-no-fill}, but here is an alternative solution using tikzfadingfrompicture:

\documentclass[tikz, border=1 cm]{standalone}
\usetikzlibrary{shapes, fadings, shadings}
\begin{tikzfadingfrompicture}[name=myfading]
\pgfmathsetmacro{\l}{3}
\node[transparent!0,draw,thick,ellipse] (S) at (-\l,0) {Solide};
\node[transparent!0,draw,thick,ellipse] (L) at (\l,0) {Liquide};
\node[transparent!0,draw,thick,ellipse] (G) at (0,{\l*sqrt(3)}) {Gaz};
\draw[transparent!0, thick ,-latex] (S) to[bend left] (G);
\draw[transparent!0, thick ,-latex] (G) to[bend left] (L);
\draw[transparent!0, thick ,-latex] (L) to[bend left] (S);
\draw[transparent!0, thick ,-latex] (S) to (L);
\draw[transparent!0, thick ,-latex] (L) to (G);
\draw[transparent!0, thick ,-latex] (G) to (S);
\end{tikzfadingfrompicture}
\begin{document}
\begin{tikzpicture}
\draw[lower left=red, lower right=blue, upper left=green, upper right=green, path fading=myfading, fit fading=false] (-3.9,-3.3) rectangle (4.1,3.5);
\end{tikzpicture}
\end{document}

Edit:

I just got an idea of how to prevent translation of the tikzfadingfrompicture - simply add a circle centered at (0,0) that encompasses everything.

\draw[transparent!100] (0,0) circle (6);. Now the nodes can be drawn outside the fading, if so desired:

\documentclass[tikz, border=1 cm]{standalone}
\usetikzlibrary{shapes, fadings, shadings}
\begin{tikzfadingfrompicture}[name=myfading]
\node[transparent!100,draw,thick,ellipse] (S) at (-3,0) {Solide};
\node[transparent!100,draw,thick,ellipse] (L) at (3,0) {Liquide};
\node[transparent!100,draw,thick,ellipse] (G) at (0,{3*sqrt(3)}) {Gaz};
\draw[transparent!0, thick ,-latex] (S) to[bend left] (G);
\draw[transparent!0, thick ,-latex] (G) to[bend left] (L);
\draw[transparent!0, thick ,-latex] (L) to[bend left] (S);
\draw[transparent!0, thick ,-latex] (S) to (L);
\draw[transparent!0, thick ,-latex] (L) to (G);
\draw[transparent!0, thick ,-latex] (G) to (S);
\draw[transparent!100] (0,0) circle (6);
\end{tikzfadingfrompicture}
\begin{document}
\begin{tikzpicture}
\draw[lower left=red, lower right=blue, upper left=green, upper right=green, path fading=myfading, fit fading=false] (-4,-1.2) rectangle (4.1,5.8);
\node[red,draw,thick,ellipse] (S) at (-3,0) {Solide};
\node[blue,draw,thick,ellipse] (L) at (3,0) {Liquide};
\node[green,draw,thick,ellipse] (G) at (0,{3*sqrt(3)}) {Gaz};
\end{tikzpicture}
\end{document}