Hi all,

I want to know how to create animation, from semicircle become cone then torus like this? So People can imagine how it looks like.

This is called Solids of Revolution: Method of Disks. When a plane region revolved about a fixed line.

I created the copy with Tikz not with Julia:

```
\documentclass[tikz]{standalone}
\begin{document}
\begin{tikzpicture}
% big circle
\draw(2,-1) arc (-90:90:2.5 and 2);% half circle facing left
\draw(2,-1) arc (-90:90:-2.5 and 2);% half circle facing right
% left circle
\draw (0.33,-0.5) arc (-90:90:-0.25 and 1.5);% left half of the left circle
\draw[dashed] (0.33,-0.5) arc (-90:90:0.25 and 1.5);% right half of the left circle
% middle circle
\draw(2,-1) arc (-90:90:-0.3 and 2);% left half of the middle circle
\draw[dashed] (2,-1) arc (-90:90:0.3 and 2);% right half of the middle circle
% right circle
\draw (3.67,-0.5) arc (-90:90:-0.25 and 1.5);% left half of the right circle
\draw[dashed] (3.67,-0.5) arc (-90:90:0.25 and 1.5);% right half of the right circle
%\draw (4,1.5) ellipse (0.5 and 1.5);% a circle / the right ellipse
\draw (-1.25,1.5) node {$\phi$};
% x ticks
\draw (-0.7,1) -- (4.7,1);% middle line / diameter
% Right image / Cone
% left circle
\draw (7.73,0.5) arc (-90:90:-0.25 and 0.5);% left half of the left circle
\draw[dashed] (7.73,0.5) arc (-90:90:0.25 and 0.5);% right half of the left circle
% middle circle
\draw(9,0.1) arc (-90:90:-0.3 and 0.9);% left half of the middle circle
\draw[dashed] (9,0.1) arc (-90:90:0.3 and 0.9);% right half of the middle circle
% right circle
\draw (10.88,-0.5) arc (-90:90:-0.35 and 1.5);% left half of the right circle
\draw (10.88,-0.5) arc (-90:90:0.35 and 1.5);% right half of the right circle
%\draw (4,1.5) ellipse (0.5 and 1.5);% a circle / the right ellipse
\draw (5.25,1.5) node {$\phi_{2}$};
% upper line / upper pythagoras
\draw (6,1) -- (10.88,2.5);% middle line / diameter
% lower line / lower pythagoras
\draw (6,1) -- (10.88,-0.5);% middle line / diameter
% middle line
\draw (6,1) -- (11.7,1);% middle line / diameter
\end{tikzpicture}
\end{document}
```

It is not Tikz discourse, but I share Tikz code if that is allowed…