TiKZ drawing routine or function

Question

Say I wanted to define a function in TiKz for drawing an eye:

\begin{tikzpicture}

%eye
\pgfmathsetmacro{\eyeSize}{1}
\pgfmathsetmacro{\ex}{0}
\pgfmathsetmacro{\ey}{1}
\pgfmathsetmacro{\eRot}{-10}
\pgfmathsetmacro{\eAp}{-55}
\draw[rotate around={\eRot:(\ex,\ey)}] (\ex,\ey) -- ++(-.5*\eAp:\eyeSize)
     (\ex,\ey) -- ++(.5*\eAp:\eyeSize);
\draw (\ex,\ey) ++(\eRot+\eAp:.75*\eyeSize) arc (\eRot+\eAp:\eRot-\eAp:.75*\eyeSize);

% IRIS
\draw[fill=gray] (\ex,\ey) ++(\eRot+\eAp/3:.75*\eyeSize) % start point
  arc (\eRot+180-\eAp:\eRot+180+\eAp:.28*\eyeSize);

%PUPIL, a filled arc 
\draw[fill=black] (\ex,\ey) ++(\eRot+\eAp/3:.75*\eyeSize) % start point
  arc (\eRot+\eAp/3:\eRot-\eAp/3:.75*\eyeSize);

\end{tikzpicture}

This is too long! How would I define a "function" in TiKz, so that I can call something \eye( \ex, \ey, \rotation, \eyeAperture ) to produce an eye?

Answer 1

Like this?

\documentclass[parskip]{scrartcl}
\usepackage[margin=15mm]{geometry}
\usepackage{tikz}

\begin{document}

\newcommand{\eye}[4]% size, x, y, rotation
{   \draw[rotate around={#4:(#2,#3)}] (#2,#3) -- ++(-.5*55:#1) (#2,#3) -- ++(.5*55:#1);
    \draw (#2,#3) ++(#4+55:.75*#1) arc (#4+55:#4-55:.75*#1);
    % IRIS
    \draw[fill=gray] (#2,#3) ++(#4+55/3:.75*#1) arc (#4+180-55:#4+180+55:.28*#1);
    %PUPIL, a filled arc 
    \draw[fill=black] (#2,#3) ++(#4+55/3:.75*#1) arc (#4+55/3:#4-55/3:.75*#1);
}

\begin{tikzpicture}
    \eye{1}{0}{1}{-10}
    \eye{2}{4}{0}{30}
    \eye{0.5}{0}{-3}{135}
    \eye{3}{4}{-4}{260}
\end{tikzpicture}

\end{document}

Answer 2

A complement to Tom's answer. I added pgfkeys stuff

\documentclass[parskip]{scrartcl}
\usepackage[margin=15mm]{geometry}
\usepackage{tikz}

  \makeatletter
\pgfkeys{/eye/.cd,
  x/.code           = {\def\eye@x{#1}},
  y/.code           = {\def\eye@y{#1}},
  rotation/.code    = {\def\eye@rot{#1}},
  radius/.code      = {\def\eye@rad{#1}}
  }

\newcommand{\eye}[1][]{% size, x, y, rotation  
\pgfkeys{/eye/.cd,
  x         = 0,
  y         = 0,
  rotation  = 0,
  radius    = 1
  } 
\pgfqkeys{/eye}{#1}   
   \draw[rotate around={\eye@rot:(\eye@x,\eye@y)}] 
         (\eye@x,\eye@y) -- ++(-.5*55:\eye@rad) 
         (\eye@x,\eye@y) -- ++(.5*55:\eye@rad);
   \draw (\eye@x,\eye@y) ++(\eye@rot+55:.75*\eye@rad) arc (\eye@rot+55:\eye@rot-55:.75*\eye@rad);
  % IRIS
   \draw[fill=gray] (\eye@x,\eye@y) ++(\eye@rot+55/3:.75*\eye@rad) arc (\eye@rot+180-55:\eye@rot+180+55:.28*\eye@rad);
  %PUPIL, a filled arc 
   \draw[fill=black] (\eye@x,\eye@y) ++(\eye@rot+55/3:.75*\eye@rad) arc (\eye@rot+55/3:\eye@rot-55/3:.75*\eye@rad);
}
\makeatother   

\begin{document}

\begin{tikzpicture}
    \eye[radius=1,y=1,rotation=-10]
    \eye[radius=2,x=4,rotation=30] 
\end{tikzpicture}

\end{document}