Fractal figures [closed]

Question

I have found this open source figures in a PDF document and I like the presentation and style of these fractals. Now I wanted to create similar fractals, maybe the Koch curve or the Cantor set in a similar style and my question is:

Where and how can I create such figures? Is it tikz or what program and has the author justed colored the fractal in a certain green color? Any advice on how I can achieve similar results would be appreciated.

---

Thanks to muzimuzhi Z! I found the almost perfect color shading:

\path[top color=green!10!black!60, bottom color=green!20, shading angle=-120]

Answer 1

To have each of the triangles or rectangles filled with independent gradient background, each of them have to be filled independently. This crosses out solutions based on nested decorations and lindenmayer systems.

Here is an attempt using nested pics. Not so automatic nor elegant, but it works. And hope it's a bit faster than node based solutions, like trees and graphs.

\documentclass[margin=5pt, tikz]{standalone}
%\usepackage{tikz}
\usetikzlibrary{shadings}

\newcount\sierlevel \sierlevel=4
\newdimen\siersize  \siersize=2cm

\tikzset{
  sierpinski tri/.pic={
    \ifnum\sierlevel>0
      \advance\sierlevel by -1
      \shade (30:+\siersize) -- (150:+\siersize) -- (-90:+\siersize) -- cycle;
      \divide\siersize by 2
      \path ( 90:+2\siersize) pic {sierpinski tri}
            (210:+2\siersize) pic {sierpinski tri}
            (-30:+2\siersize) pic {sierpinski tri};
    \fi
  },
  sierpinski rect/.pic={
    \ifnum\sierlevel>0
      \advance\sierlevel by -1
      \shade (-\siersize, -\siersize) rectangle (\siersize,\siersize);
      \divide\siersize by 3
      \path[x=\siersize,y=\siersize]
        foreach \x in {-1,0,1} {
          foreach \y in {-1,0,1} {
            \ifnum\numexpr\x*\x+\y*\y>0
              (7*\x,7*\y) pic {sierpinski rect}
            \fi
          }
        };
    \fi
  }
}

\begin{document}


\begin{tikzpicture}
  \siersize=2cm
  \foreach \i in {1,...,4} {
    \sierlevel=\i
    \begin{scope}[xshift=\i*8cm]
      \fill[black] 
        ( 90:+2\siersize) -- (210:+2\siersize) -- (-30:+2\siersize) -- cycle;
      \path[top color=green!50!black!30, bottom color=green!50, shading angle=-120]
        pic {sierpinski tri};
    \end{scope}
  }
\end{tikzpicture}

\begin{tikzpicture}
  \siersize=1cm
  \foreach \i in {1,...,4} {
    \sierlevel=\i
    \begin{scope}[xshift=\i*8cm]
      \fill (-3.5\siersize, -3.5\siersize) rectangle (3.5\siersize, 3.5\siersize);
      \path[top color=green!50!black!30, bottom color=green!50, shading angle=-120]
        pic {sierpinski rect};
    \end{scope}
  }
\end{tikzpicture}
\end{document}

Update: In comment @calculatormathematical suggested a much better color shading config:

% old
\path[top color=green!50!black!30, bottom color=green!50, shading angle=-120]
% new
\path[top color=green!10!black!60, bottom color=green!20, shading angle=-120]