Define new PSTricks object with arguments

Question

Inspired by Clemens Niederberger's post about a possible new package, I have tried to create a similar figure using PSTricks.

Code

\documentclass{article}

\usepackage{chemmacros}
\usepackage{pstricks-add}

\pagestyle{empty}

\begin{document}

\begin{figure}[htbp]
% Parameters
\def\basinwidth{15 }
\def\basinheight{10 }
\def\waterheight{8}
\def\cathode{\ch{Zn}}
\def\cathodeColour{gray!30}
\def\anode{\ch{Cu}}
\def\anodeColour{red!50}
\centering
\psset{unit=0.7\psunit}
\begin{pspicture}(15,11.5)
% Basin
\psline(0,\basinheight)(0,\waterheight)
\pscustom[fillstyle=solid,fillcolor=cyan!70]{%
  \psline(0,\waterheight)(\basinwidth,\waterheight)
  \psline(0,\waterheight)(0,1)
  \psarc(1,1){1}{180}{270}
  \psline(1,0)(!\basinwidth 1 sub 0)
  \psarc(!\basinwidth 1 sub 1){1}{270}{360}
  \psline(\basinwidth,1)(\basinwidth,\waterheight)
 \closepath
}
\psline(\basinwidth,\waterheight)(\basinwidth,\basinheight)
% Membrane
\psline[linestyle=dashed]%
  (!\basinwidth 2 div 0)%
  (!\basinwidth 2 div \waterheight)
% Cathode
\pspolygon[fillstyle=solid,fillcolor=\cathodeColour]%
  (!\basinwidth 4 div 1 sub 1)%
  (!\basinwidth 4 div 1 sub \basinheight 1 sub)%
  (!\basinwidth 4 div 1 add \basinheight 1 sub)%
  (!\basinwidth 4 div 1 add 1)
\rput(!\basinwidth 4 div \basinheight 2 div){\cathode}
% Anode
\pspolygon[fillstyle=solid,fillcolor=\anodeColour]%
  (!3 \basinwidth mul 4 div 1 sub 1)%
  (!3 \basinwidth mul 4 div 1 sub \basinheight 1 sub)%
  (!3 \basinwidth mul 4 div 1 add \basinheight 1 sub)%
  (!3 \basinwidth mul 4 div 1 add 1)
\rput(!3 \basinwidth mul 4 div \basinheight 2 div){\anode}
% Wires
\rput(!\basinwidth 4 div 1 add \basinheight){$+$}
\psline(!\basinwidth 4 div \basinheight 1 sub)%
       (!\basinwidth 4 div \basinheight)
\psarc(!\basinwidth 4 div 1 add \basinheight){1}{90}{180}
\psline(!\basinwidth 4 div 1 add \basinheight 1 add)%
       (!\basinwidth 1 sub 2 div \basinheight 1 add)
\pscircle(!\basinwidth 2 div \basinheight 1 add){0.5}
\rput(!\basinwidth 2 div \basinheight 1 add){$U$}
\psline(!3 \basinwidth mul 4 div 1 sub \basinheight 1 add)%
       (!\basinwidth 1 add 2 div \basinheight 1 add)
\psarc(!3 \basinwidth mul 4 div 1 sub \basinheight){1}{0}{90}
\psline(!3 \basinwidth mul 4 div \basinheight 1 sub)%
       (!3 \basinwidth mul 4 div \basinheight)
\rput(!3 \basinwidth mul 4 div 1 sub \basinheight){$-$}
% Electron movement
\rput(!3 \basinwidth mul 1 add 8 div \basinheight 3 2 div add)%
     {\ch{->[ e- ]}}
\rput(!5 \basinwidth mul 2 sub 8 div \basinheight 3 2 div add)%
     {\ch{->[ e- ]}}
\end{pspicture}
\end{figure}

\end{document}

The code should be compiled with xelatex.

Question

Is it possible to define a new object with argument that looks something like the following?

\cell[
  cathode=Zn,
  cathodeColour=grey!30,
  anode=Cu,
  anodeColour=red!50
]{"basinwidth"}{"basinheight"}{"waterheight"}

If it is possible, how do I do it?

Extra question

I have had a look at section 28.2 in the chemmacros manual in order to draw the arrows with electrons above but I couldn't make it work with \ch{ ->[\el] }. If someone can tell be how to draw this, that would be nice. (Solved)

Answer 1

I have no experience whatsoever with PSTricks so I don't know if there are preferred ways to what I am going to suggest. It seems to me that this is a straight-forward task: wrap the whole definition in a macro with an optional argument. PSTricks loads xkeyval so you can use this package to define keys which then can be set by the optional argument:

% default definitions:
\def\cathode{\ch{Zn}}
\def\cathodeColour{gray!30}
\def\anode{\ch{Cu}}
\def\anodeColour{red!50}

\makeatletter
% keys for the optional argument:
\define@key{cell}{cathode}{\def\cathode{\ch{#1}}}
\define@key{cell}{cathodeColour}{\def\cathodeColour{#1}}
\define@key{cell}{anode}{\def\anode{\ch{#1}}}
\define@key{cell}{anodeColour}{\def\anodeColour{#1}}
\makeatother

% \cell[<options>]{<basinwidth>}{<basinheight>}{<waterheight>}
\newcommand\cell[4][]{%
 \begingroup
  % set the keys:
  \setkeys{cell}{#1}%
  \def\basinwidth{#2 }%
  \def\basinheight{#3 }%
  \def\waterheight{#4 }%
  % the rest of the definition:
  ...
 \endgroup

The grouping is to keep the setting of the keys local. However, since they're going to be used in a pspicture it's probably not needed. If you want to be able to access coordinates of the cell it's probably even better to omit it, anyway. (As I said: I have no experience with PSTricks so I haven't tested this...)

Here's an entire example based on your example code:

\documentclass{article}

\usepackage{chemmacros}
\usepackage{pstricks-add}

\pagestyle{empty}

\def\cathode{\ch{Zn}}
\def\cathodeColour{gray!30}
\def\anode{\ch{Cu}}
\def\anodeColour{red!50}

\makeatletter
\define@key{cell}{cathode}{\def\cathode{\ch{#1}}}
\define@key{cell}{cathodeColour}{\def\cathodeColour{#1}}
\define@key{cell}{anode}{\def\anode{\ch{#1}}}
\define@key{cell}{anodeColour}{\def\anodeColour{#1}}
\makeatother

\newcommand\cell[4][]{%
 \begingroup
  \setkeys{cell}{#1}%
  \def\basinwidth{#2 }%
  \def\basinheight{#3 }%
  \def\waterheight{#4 }%
% Basin
\psline(0,\basinheight)(0,\waterheight)
\pscustom[fillstyle=solid,fillcolor=cyan!70]{%
  \psline(0,\waterheight)(\basinwidth,\waterheight)
  \psline(0,\waterheight)(0,1)
  \psarc(1,1){1}{180}{270}
  \psline(1,0)(!\basinwidth 1 sub 0)
  \psarc(!\basinwidth 1 sub 1){1}{270}{360}
  \psline(\basinwidth,1)(\basinwidth,\waterheight)
 \closepath
}
\psline(\basinwidth,\waterheight)(\basinwidth,\basinheight)
% Membrane
\psline[linestyle=dashed]%
  (!\basinwidth 2 div 0)%
  (!\basinwidth 2 div \waterheight)
% Cathode
\pspolygon[fillstyle=solid,fillcolor=\cathodeColour]%
  (!\basinwidth 4 div 1 sub 1)%
  (!\basinwidth 4 div 1 sub \basinheight 1 sub)%
  (!\basinwidth 4 div 1 add \basinheight 1 sub)%
  (!\basinwidth 4 div 1 add 1)
\rput(!\basinwidth 4 div \basinheight 2 div){\cathode}
% Anode
\pspolygon[fillstyle=solid,fillcolor=\anodeColour]%
  (!3 \basinwidth mul 4 div 1 sub 1)%
  (!3 \basinwidth mul 4 div 1 sub \basinheight 1 sub)%
  (!3 \basinwidth mul 4 div 1 add \basinheight 1 sub)%
  (!3 \basinwidth mul 4 div 1 add 1)
\rput(!3 \basinwidth mul 4 div \basinheight 2 div){\anode}
% Wires
\rput(!\basinwidth 4 div 1 add \basinheight){$+$}
\psline(!\basinwidth 4 div \basinheight 1 sub)%
       (!\basinwidth 4 div \basinheight)
\psarc(!\basinwidth 4 div 1 add \basinheight){1}{90}{180}
\psline(!\basinwidth 4 div 1 add \basinheight 1 add)%
       (!\basinwidth 1 sub 2 div \basinheight 1 add)
\pscircle(!\basinwidth 2 div \basinheight 1 add){0.5}
\rput(!\basinwidth 2 div \basinheight 1 add){$U$}
\psline(!3 \basinwidth mul 4 div 1 sub \basinheight 1 add)%
       (!\basinwidth 1 add 2 div \basinheight 1 add)
\psarc(!3 \basinwidth mul 4 div 1 sub \basinheight){1}{0}{90}
\psline(!3 \basinwidth mul 4 div \basinheight 1 sub)%
       (!3 \basinwidth mul 4 div \basinheight)
\rput(!3 \basinwidth mul 4 div 1 sub \basinheight){$-$}
% Electron movement
\rput(!3 \basinwidth mul 1 add 8 div \basinheight 3 2 div add)%
     {\ch{->[ e- ]}}
\rput(!5 \basinwidth mul 2 sub 8 div \basinheight 3 2 div add)%
     {\ch{->[ e- ]}}
 \endgroup
}

\begin{document}

\begin{figure}[htbp]
 \centering
 \psset{unit=0.7\psunit}
 \begin{pspicture}(15,11.5)
  \cell{15}{10}{8}
 \end{pspicture}
\end{figure}

\begin{figure}[htbp]
 \centering
 \psset{unit=0.7\psunit}
 \begin{pspicture}(15,11.5)
  \cell[
    cathode=Cu,
    cathodeColour=red!50,
    anode=Ag,
    anodeColour=gray!10
  ]{15}{10}{8}
 \end{pspicture}
\end{figure}

\end{document}