disc.tex

% Stacked disks
% Author: Mark Wibrow
\documentclass[tikz,border=10pt]{standalone}
%%%<
\usepackage{verbatim}
%%%>
\begin{comment}
:Title: Stacked discs in 3d
:Tags: Foreach;Pic;3d;Decorative drawings
:Author: Mark Wibrow
:Slug: disc

To draw a stack of disks with a 3d impression, we use
the pic element, which is new in TikZ 3.0 and can be considered
like combining a node and a tikzpicture.

This example was written by Mark Wibrow answering a question on TeX.SE.
\end{comment}
\tikzset{
  pics/.cd,
  disc/.style = {
    code = {
      \fill [white] ellipse [x radius = 2, y radius = 2/3];
      \path [left color = black!50, right color = black!50,
        middle color = black!25] 
        (-2+.05,-1.1) arc (180:360:2-.05 and 2/3-.05*2/3) -- cycle;
      \path [top color = black!25, bottom color = white] 
        (0,.05*2/3) ellipse [x radius = 2-.05, y radius = 2/3-.05*2/3];
      \path [left color = black!25, right color = black!25,
        middle color = white] (-2,0) -- (-2,-1) arc (180:360:2 and 2/3)
        -- (2,0) arc (360:180:2 and 2/3);
      \foreach \r in {225,315}
        \foreach \i [evaluate = {\s=30;}] in {0,2,...,30}
          \fill [black, fill opacity = 1/50] 
            (0,0) -- (\r+\s-\i:2 and 2/3) -- ++(0,-1) 
            arc (\r+\s-\i:\r-\s+\i:2 and 2/3) -- ++(0,1) -- cycle;
      \foreach \r in {45,135}
        \foreach \i [evaluate = {\s=30;}] in {0,2,...,30}
          \fill [black, fill opacity = 1/50] 
            (0,0) -- (\r+\s-\i:2 and 2/3) 
            arc (\r+\s-\i:\r-\s+\i:2 and 2/3)  -- cycle;
    }
  },
  disc bottom/.style = {
    code = {
      \foreach \i in {0,2,...,30}
        \fill [black, fill opacity = 1/60] (0,-1.1)
          ellipse [x radius = 2+\i/40, y radius = 2/3+\i/60];
      \path pic {disc};
    }
  }
}
\begin{document}
\begin{tikzpicture}
\path (0,0) pic {disc bottom} (0,1.25) pic {disc} (0,2.5) pic {disc};
\end{tikzpicture}
\end{document}