Add spark gap

Closes circuitikz#800

CHANGELOG.md

@@ -6,6 +6,7 @@ The major changes among the different CircuiTikZ versions are listed here. See <
     - Added a Relais-Shape (contributed by [Jakob "DraUX" on GitHub](https://github.com/circuitikz/circuitikz/pull/795)
     - Added a center tap anchor for tube's filament (suggested by [user bogger33 on GitHub](https://github.com/circuitikz/circuitikz/issues/792))
     - Added neon lamps (two versions, suggested by [user bogger33 on GitHub](https://github.com/circuitikz/circuitikz/issues/793))
+    - Added a configurable spark gap (suggested by [user bogger33 on GitHub](https://github.com/circuitikz/circuitikz/issues/800))
     - Fix a long-standing problem when [(locally) switching diode type](https://github.com/circuitikz/circuitikz/issues/794)
 
 * Version 1.6.8 (2024-05-05)

doc/circuitikzmanual.tex

@@ -3292,6 +3292,10 @@ \subsection{Miscellaneous bipoles}
     \circuitdescbip*{neonlampcc}{Neon lamp\footnotemark\ (double cathode style)}{}
      \footnotetext{The neon lamps have been added in \texttt{v1.6.9}  thanks to a suggestion by \href{https://github.com/circuitikz/circuitikz/issues/793}{user bogger33 on GitHub}.}
     \circuitdescbip*{neonlampac}{Neon lamp (anode and cathode style)}{}
+    \circuitdescbip*{sparkgap}{Spark gap\footnotemark (unenclosed)}{}
+     \footnotetext{The spark gap has been added in \texttt{v1.6.9}  thanks to a suggestion by \href{https://github.com/circuitikz/circuitikz/issues/800}{user bogger33 on GitHub}.}
+     \circuitdescbip*[sparkgap]{sparkgap, sparkgap/circle}{Spark gap}{}
+    \circuitdescbip*[sparkgap]{sparkgap, sparkgap/dot, sparkgap/circle}{Spark gap (gas filled)}{}
     \circuitdescbip*{loudspeaker}{loudspeaker}{}( north/90/0.4, ne/45/0.4, east/0/0.4, se/-45/0.4, south/-90/0.4, sw/-135/0.4, west/180/0.4, nw/135/0.4, left/135/0.2, right/45/0.2, center/-135/0.2)
     \circuitdescbip*{mic}{mic}{}( north/90/0.4, east/0/0.4,  south/-90/0.4,  west/180/0.4, left/135/0.2, right/45/0.2, center/-135/0.2)
     \circuitdescbip*{tlmic}{tail-less mic\footnotemark}{}( north/90/0.4,  east/0/0.4,  south/-90/0.4, west/180/0.4,  left/135/0.2, right/45/0.2, center/-135/0.2)
@@ -3331,7 +3335,7 @@ \subsubsection{Miscellaneous element customization}\label{sec:tweak-misc}
 
 You can change the scale of all the miscellaneous elements by setting the key \texttt{misc/scale} to something different from the default \texttt{1.0}; relative thickness can be controlled with \texttt{misc/thickness}.
 
-\paragraph{Wiggly fuses} can have (or not have) poles; you can switch between the two forms by setting to \texttt{true} or \texttt{false} (default \texttt{true}) the key \texttt{bipoles/wfuse/dots}; if they have poles, you can choose any of the pole shapes with the key \texttt{bipoles/wfuse/shape}.
+\paragraph{Wiggly fuses.} Wiggly fuses can have (or not have) poles; you can switch between the two forms by setting to \texttt{true} or \texttt{false} (default \texttt{true}) the key \texttt{bipoles/wfuse/dots}; if they have poles, you can choose any of the pole shapes with the key \texttt{bipoles/wfuse/shape}.
 The pole nodes are named \texttt{-left} and \texttt{-right} so that you can access their borders.
 
 \begin{LTXexample}[varwidth=true, basicstyle=\small\ttfamily]
@@ -3347,14 +3351,30 @@ \subsubsection{Miscellaneous element customization}\label{sec:tweak-misc}
 \end{circuitikz}
 \end{LTXexample}
 
-\paragraph{Neon lamps} ``dot'' size is the same as the size of poles (\texttt{circ} and \texttt{ocirc}), and they can be changed locally:
+\paragraph{Neon lamps.} Neon lamp ``dot'' size is the same as the size of poles (\texttt{circ} and \texttt{ocirc}), and they can be changed locally:
 \begin{LTXexample}[varwidth=true, basicstyle=\small\ttfamily]
 \begin{tikzpicture}
     \draw (0,0) to[neonlampcc, nodes width=0.03] ++(2,0)
         to[neonlampac, misc/thickness=3] ++(2,0);
 \end{tikzpicture}
 \end{LTXexample}
 
+\paragraph{Spark gap.} The \texttt{sparkgap} component is similar to the (American) surge arrester, but it's more configurable; it will render bare (unenclosed) by default, but you can add a (fillable) enclosure with the key \texttt{sparkgap/circle} and a dot with \texttt{sparkgap/dot} (they are boolean keys, false by default).
+Moreover, the arrows are configurable like other arrows in the package (see~\ref{sec:tunablearrows}) using the \texttt{sparkgap end arrow} key (default \texttt{Triangle[scale=2]}). The gap is tunable with \texttt{sparkgap/gap} (default \texttt{0.05}).
+\begin{LTXexample}[varwidth=true, basicstyle=\small\ttfamily]
+\begin{tikzpicture}
+    \draw (0,2) to[sparkgap, l=gap\textsubscript{1}] ++(2,0)
+         to[sparkgap, sparkgap/circle,
+            sparkgap/dot, l=S2] ++(2,0);
+     \ctikzset{sparkgap end arrow={Kite[scale=1.5]}}
+     \draw (0,0) to[sparkgap, l=S3] ++(2,0)
+         to[sparkgap, l=S4, sparkgap/circle,
+         sparkgap/gap=0.15] ++(2,0);
+\end{tikzpicture}
+\end{LTXexample}
+As in neon lamps, the dot (if activated by the key \texttt{sparkgap/dot}) follows the size of poles and can be changed locally.
+
+
 \subsection{Multiple wires (buses)}
 
 These are simple drawings to indicate multiple wires.

tex/pgfcircbipoles.tex

@@ -7010,6 +7010,13 @@
 % suggested by @bogger33, see https://github.com/circuitikz/circuitikz/issues/793
 \ctikzset{bipoles/neonlampcc/height/.initial=.60}
 \ctikzset{bipoles/neonlampac/height/.initial=.60}
+\pgf@circ@declare@family@arrows{sparkgap}
+\newif\ifpgf@sparkgap@dot
+\newif\ifpgf@sparkgap@circle
+\ctikzset{sparkgap/circle/.is if=pgf@sparkgap@circle}
+\ctikzset{sparkgap/dot/.is if=pgf@sparkgap@dot}
+\ctikzset{sparkgap/gap/.initial=.05}
+\ctikzset{bipoles/sparkgap/height/.initial=.60}
 %
 \ctikzset{bipoles/squid/height/.initial=.60}
 \ctikzset{bipoles/squid/width/.initial=.60}
@@ -7431,7 +7438,42 @@
     \pgftransformshift{\pgfpoint{-\@@w\pgf@circ@res@right}{\@@h\pgf@circ@res@down}}
     \pgfnode{circ}{center}{}{}{\pgfusepath{draw,fill}}
 }
-
+% spark gap, suggested by @bogger33 https://github.com/circuitikz/circuitikz/issues/800
+\pgfcircdeclarebipolescaled{misc}
+{
+    \savedmacro{\changeh}{\edef\changeh{\ifpgf@sparkgap@circle 1 \else 0.5 \fi}}
+    \pgfcirc@border@extend@updown{\changeh}{\changeh}
+}
+{\ctikzvalof{bipoles/sparkgap/height}}
+{sparkgap}
+{\ctikzvalof{bipoles/sparkgap/height}}
+{\ctikzvalof{bipoles/sparkgap/height}}{
+    % circle (if requested)
+    \pgfscope
+        \ifpgf@sparkgap@circle
+            \pgf@circ@setlinewidth{bipoles}{\pgfstartlinewidth}
+            \pgfpathcircle{\pgfpointorigin}{\pgf@circ@res@up}
+            \pgf@circ@draworfill
+        \fi
+    \endpgfscope
+    % arrows
+    \pgfscope
+        \pgfcirc@set@arrows{sparkgap}{}{Triangle[scale=2]}
+        \pgfpathmoveto{\pgfpoint{\pgf@circ@res@right}{0pt}}
+        \pgfpathlineto{\pgfpoint{\ctikzvalof{sparkgap/gap}\pgf@circ@res@right}{0pt}}
+        \pgfusepath{draw}
+        \pgfpathmoveto{\pgfpoint{\pgf@circ@res@left}{0pt}}
+        \pgfpathlineto{\pgfpoint{\ctikzvalof{sparkgap/gap}\pgf@circ@res@left}{0pt}}
+        \pgfusepath{draw}
+    \endpgfscope{}
+    % dot (if requested)
+    \ifpgf@sparkgap@dot
+        \pgftransformshift{\pgfpoint
+            {\ctikzvalof{sparkgap/gap}\pgf@circ@res@left-1*\ctikzvalof{nodes width}\pgf@circ@Rlen}
+            {-4*\ctikzvalof{nodes width}\pgf@circ@Rlen}}
+        \pgfnode{circ}{center}{}{}{\pgfusepath{draw,fill}}
+    \fi
+}
 
 %>>>
 
@@ -7440,6 +7482,7 @@
 \pgfcirc@activate@bipole@simple{l}{lamp}
 \pgfcirc@activate@bipole@simple{l}{neonlampcc}
 \pgfcirc@activate@bipole@simple{l}{neonlampac}
+\pgfcirc@activate@bipole@simple{l}{sparkgap}
 \pgfcirc@activate@bipole@simple{l}{bulb}
 \pgfcirc@activate@bipole@simple{l}{squid}
 \pgfcirc@activate@bipole@simple{l}{barrier}