I see [this question](https://tex.stackexchange.com/questions/462774/drawing-a-tank-with-water-in-it)  How to draw it with 3dtools?
Here is a simplistic way of doing this.
```
\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{calc,3dtools}% https://github.com/marmotghost/tikz-3dtools
\begin{document}
\begin{tikzpicture}[line cap=round,line join=round,
3d/install view={phi=0,theta=70},
declare function={R=3;H=4;h=2.5;},
same bounding box=A]
\fill[blue] (-R,0,0) arc[start angle=180,end angle=360,radius=R]
-- (R,0,h) arc[start angle=360,end angle=180,radius=R] -- cycle;
\pgfmathtruncatemacro{\itest}{screendepth(0,0,1)<0?0:1}
\ifnum\itest=0
\fill[blue!50] (0,0,0) circle[radius=R];
\else
\fill[blue!50] (0,0,h) circle[radius=R];
\fi
\pic{3d/frustum={r=R,R=R,h=H}};
\end{tikzpicture}
\end{document}
```
All these pics are far from perfect. The first one is not rotatable. The second one is better but would require one to build in a number of checks, For instance, if the slope is too large (or the height too small) it cannot be drawn. That is, the more complicated, specialized or restricted the pics become, the more likely it becomes that users find the whole library useless. Therefore, I'd prefer not to add such pics.
@marmot, re: [your answer](#a1974), 
@marmot, re: [your answer](#a1974), And this is your code about cylinderal segment. Can you add it into `3dtools` by using a `pic`? like this
`\pic{3d/cylindrical segment ={r=r,h1=, h2=}};`
```
\documentclass[border=1mm,12pt,tikz]{standalone}
\usetikzlibrary{3dtools,calc}% https://github.com/marmotghost/tikz-3dtools
\begin{document}
\foreach \Angle in {5}
{\begin{tikzpicture}[3d/install view={phi=\Angle,psi=0,theta=70},
line join = round, line cap = round,c/.style={circle,fill,inner sep=1pt},
same bounding box=A,
declare function={h1=5;h2=0;myR=3;}]
\path[overlay]
(0,0,0) coordinate (O)
(-myR,0,h1) coordinate (H1)
(myR,0,h2) coordinate (H2)
(0,myR,0.5*h1+0.5*h2) coordinate (H3);
\pgfmathsetmacro{\myscreenex}{TDunit("(0,0,1)x(nscreenx,nscreeny,nscreenz)")}
\path[3d coordinate={(L)=-myR*(\myscreenex)},
3d coordinate={(R)=myR*(\myscreenex)}];
\pgfmathsetmacro{\myF}{TDunit("(\myscreenex)x(0,0,1)")}
\pgfmathsetmacro{\myF}{TD("myR*(\myF)")}
\path (\myF) coordinate (F);
\pgfmathsetmacro{\myn}{TDunit("(H2)-(H1)x(0,1,0)")}
\tikzset{3d/plane with normal={(\myn) through (H1) named p},
3d/line with direction={(0,0,1) through (L) named l1},
3d/line with direction={(0,0,1) through (R) named l2},
3d/line with direction={(0,0,1) through (O) named l3},
3d/line with direction={(0,0,1) through (F) named l4}}
\path[3d/intersection of={l1 with p}] coordinate (L');
\path[3d/intersection of={l2 with p}] coordinate (R');
\path[3d/intersection of={l3 with p}] coordinate (O');
\path[3d/intersection of={l4 with p}] coordinate (F');
\path (O) pic{3d/circle on sphere={R=myR,n={(0,0,1)}}};
\draw[3d/visible] (L) -- (L') (R) -- (R');
\pgfmathsetmacro{\myRp}{tddistance("(H2)","(O')")}
\tikzset{3d/define orthonormal dreibein={A={(O')},B={(H3)},C={(H2)}}}
\pgfmathsetmacro{\myphi}{atan2(TD("(0,1,0)o(\myscreenex)"),TD("(1,0,0)o(\myscreenex)"))}
\pgfmathtruncatemacro{\itest}{screendepth(\myn)>0?1:0}
\begin{scope}[x={(ex)},y={(ey)},z={(ez)},shift={(O')}]
\ifnum\itest=1
\draw[3d/visible] (O') circle[x radius=myR,y radius=\myRp];
\else
\draw[3d/hidden]
(90-\myphi:myR and \myRp) arc[start angle=90-\myphi,end angle=90-\myphi-180,x radius=myR,y radius=\myRp];
\draw[3d/visible]
(90-\myphi:myR and \myRp) arc[start angle=90-\myphi,end angle=90-\myphi+180,x radius=myR,y radius=\myRp];
\fi
\end{scope}
%\path foreach \p/\g in {L/180,R/0,L'/180,R'/0,O'/0,F/-90,F'/90,O'/0,H3/0,H2/0}{(\p)node[c]{}+(\g:2.5mm) node{$\p$}};
\end{tikzpicture}}
\end{document}
```
Can you add a pic, e.g `\pic{3d/oblique cylinder ={r=r,h=h,dx=dx}};` into `3dtools`
```
\documentclass[tikz,border=3.14mm]{standalone}
\usetikzlibrary{3dtools,calc}% https://github.com/marmotghost/tikz-3dtools
\begin{document}
\begin{tikzpicture}[3d/install view={phi=00,theta=70},
line cap=butt,line join=round,c/.style={circle,fill,inner sep=1pt},
declare function={R=1.5;dx=2;h=3;}]
\path (0,0,0) coordinate (O) (dx,0,h) coordinate (O');
\pgfmathsetmacro{\myex}{TDunit("(0,0,1)x(nscreenx,nscreeny,nscreenz)")}%
\pgfmathsetmacro{\myey}{TDunit("(0,0,1)x(\myex)")}%
\path (0,0,1) coordinate (ez) (\myey) coordinate (ey) (\myex) coordinate (ex);
\pgfmathsetmacro{\sdtip}{screendepth(0,0,h)}
\pgfmathsetmacro{\aspectangle}{atan2(\sdtip,sqrt(h*h-\sdtip*\sdtip))}
\begin{scope}[x={(ex)},y={(ey)},z={(ez)}]
\pgfmathsetmacro{\alphacrit}{acos(tan(\aspectangle)*R/h)-90}
\draw[3d/hidden] (\alphacrit:R)
arc[start angle=\alphacrit,end angle=180+\alphacrit,radius=R];
\draw
% the following two lines are for the shading, if you comment them
% you will not get shading
let \p1=($(O')-(O)$),\n1={atan2(\y1,\x1)} in
[]
(\alphacrit:R) -- ($(O')+(\alphacrit:R)$)
arc[start angle=\alphacrit,end angle=-180+\alphacrit,radius=R]
-- (-180+\alphacrit:R)
arc[start angle=-180+\alphacrit,end angle=\alphacrit,radius=R] ;
\draw[3d/visible] (O') circle[radius=R];
\end{scope}
\end{tikzpicture}
\end{document}
```
To produce something like the screen picture you show, you can use the following code (which is not fully rotatable).
```
\documentclass[tikz,border=3.14mm]{standalone}
\usetikzlibrary{3dtools,calc}% https://github.com/marmotghost/tikz-3dtools
\begin{document}
\begin{tikzpicture}[3d/install view={phi=00,theta=70},
line cap=butt,line join=round,c/.style={circle,fill,inner sep=1pt},
declare function={R=1.5;dx=1;h=3;}]
\path (0,0,0) coordinate (O) (dx,0,h) coordinate (O');
\pgfmathsetmacro{\myex}{TDunit("(0,0,1)x(nscreenx,nscreeny,nscreenz)")}%
\pgfmathsetmacro{\myey}{TDunit("(0,0,1)x(\myex)")}%
\path (0,0,1) coordinate (ez) (\myey) coordinate (ey) (\myex) coordinate (ex);
\pgfmathsetmacro{\sdtip}{screendepth(0,0,h)}
\pgfmathsetmacro{\aspectangle}{atan2(\sdtip,sqrt(h*h-\sdtip*\sdtip))}
\begin{scope}[x={(ex)},y={(ey)},z={(ez)}]
\pgfmathsetmacro{\alphacrit}{acos(tan(\aspectangle)*R/h)-90}
\draw[3d/hidden] (\alphacrit:R)
arc[start angle=\alphacrit,end angle=180+\alphacrit,radius=R];
\draw
% the following two lines are for the shading, if you comment them
% you will not get shading
let \p1=($(O')-(O)$),\n1={atan2(\y1,\x1)} in
[left color=red,right color=red,middle color=white,shading angle=\n1]
(\alphacrit:R) -- ($(O')+(\alphacrit:R)$)
arc[start angle=\alphacrit,end angle=-180+\alphacrit,radius=R]
-- (-180+\alphacrit:R)
arc[start angle=-180+\alphacrit,end angle=\alphacrit,radius=R] ;
\draw[3d/visible,fill=cyan] (O') circle[radius=R];
\end{scope}
\end{tikzpicture}
\end{document}
```
@marmot, re: [your answer](#a1974),  How can I draw Oblique cylinder like above picture? I see [here](https://en.wikipedia.org/wiki/Cylinder)
Yes, I agree. Also you can rotate objects. In the "projection by hand" scheme there is no well-defined notion of rotating things (but of course in perspective projections there is).
I like orthographic projections. You do not need ware of any automatic way to always find an appropriate function for non-orthographic projections.
For instance, this redefinition of `screendepth` works:
```
\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{calc,3dtools}% https://github.com/marmotghost/tikz-3dtools
\begin{document}
\begin{tikzpicture}[3d/install view={phi=300,theta=70},line cap=butt,
line join=round,c/.style={circle,fill,inner sep=1pt},
declare function={a=3;},
y={(1cm,0)}]
\pgfmathdeclarefunction*{screendepth}{3}{\pgfmathparse{-1*#1+0.2*#2+0.5*#3}}
\path
(a,-a,-a) coordinate (A)
(a,a,-a) coordinate (B)
(-a,a,-a) coordinate (C)
(-a,-a,-a) coordinate (D)
(a,-a,a) coordinate (E)
(a,a,a) coordinate (F)
(-a,a,a) coordinate (G)
(-a,-a,a) coordinate (H)
(0,0,0) coordinate (O)
[3d coordinate={(M)=0.5*(A) + 0.5*(H)},3d coordinate={(N)=0.5*(B) + 0.5*(G)},3d coordinate={(P)=0.5*(C) + 0.5*(H)},,3d coordinate={(Q)=0.5*(A) + 0.5*(F)} ];
\tikzset{3d/polyhedron/.cd,cr/.code n args={5}{\tikzset{3d/define orthonormal dreibein={A={(#2)},B={(#3)},C={(#4)}}}
\begin{scope}[x={(ex)},y={(ey)},z={(ez)}]
\draw[#1] ($0.25*(#2)+0.25*(#3)+0.25*(#4)+0.25*(#5)$)
circle;
\end{scope}
},4gon with circle/.style n args={5}{
after hidden/.code={
\tikzset{3d/polyhedron/cr={3d/hidden,radius=a,#1}{#2}{#3}{#4}{#5}}
},
after visible/.code={
\tikzset{3d/polyhedron/cr={3d/visible,radius=a,#1}{#2}{#3}{#4}{#5}}
},
draw face with corners={{(#2)},{(#3)},{(#4)},{(#5)}},
after hidden/.code={},after visible/.code={},
}
}
\tikzset{3d/polyhedron/.cd,O={(O)},
back/.append style={3d/hidden,fill=none},
fore/.append style={3d/visible,fill=none},
edges have complete dashes,
4gon with circle={}{D}{C}{G}{H},
4gon with circle={red}{B}{C}{G}{F},
4gon with circle={blue}{E}{F}{G}{H},
4gon with circle={green!60!black}{A}{B}{C}{D},
4gon with circle={magenta}{A}{B}{F}{E},
4gon with circle={cyan}{A}{E}{H}{D},
}
\path foreach \p/\g in {A/-90,B/-90,C/0,D/0,E/90,F/90,G/0,H/90}{(\p)node[c]{}+(\g:2.5mm) node{$\p$}};
\end{tikzpicture}
\end{document}
````
But I am not aware of any automatic way to always find an appropriate function for non-orthographic projections.Yes, `3dtools` only works with orthographic projections. `y={(1cm,0)}` destroys the orthographic projection. So you need either to be lucky or redefine the `screendepth` as illustrated in [this answer](https://topanswers.xyz/tex?q=1784#a2015).Is this code not correct for every angle? I tried with `phi=300`. I get
```
\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{calc,3dtools}% https://github.com/marmotghost/tikz-3dtools
\begin{document}
\begin{tikzpicture}[3d/install view={phi=300,theta=70},line cap=butt,
line join=round,c/.style={circle,fill,inner sep=1pt},
declare function={a=3;},
y={(1cm,0)}]
\path
(a,-a,-a) coordinate (A)
(a,a,-a) coordinate (B)
(-a,a,-a) coordinate (C)
(-a,-a,-a) coordinate (D)
(a,-a,a) coordinate (E)
(a,a,a) coordinate (F)
(-a,a,a) coordinate (G)
(-a,-a,a) coordinate (H)
(0,0,0) coordinate (O)
[3d coordinate={(M)=0.5*(A) + 0.5*(H)},3d coordinate={(N)=0.5*(B) + 0.5*(G)},3d coordinate={(P)=0.5*(C) + 0.5*(H)},,3d coordinate={(Q)=0.5*(A) + 0.5*(F)} ];
\tikzset{3d/polyhedron/.cd,cr/.code n args={5}{\tikzset{3d/define orthonormal dreibein={A={(#2)},B={(#3)},C={(#4)}}}
\begin{scope}[x={(ex)},y={(ey)},z={(ez)}]
\draw[#1] ($0.25*(#2)+0.25*(#3)+0.25*(#4)+0.25*(#5)$)
circle;
\end{scope}
},4gon with circle/.style n args={5}{
after hidden/.code={
\tikzset{3d/polyhedron/cr={3d/hidden,radius=a,#1}{#2}{#3}{#4}{#5}}
},
after visible/.code={
\tikzset{3d/polyhedron/cr={3d/visible,radius=a,#1}{#2}{#3}{#4}{#5}}
},
draw face with corners={{(#2)},{(#3)},{(#4)},{(#5)}},
after hidden/.code={},after visible/.code={},
}
}
\tikzset{3d/polyhedron/.cd,O={(O)},
back/.append style={3d/hidden,fill=none},
fore/.append style={3d/visible,fill=none},
edges have complete dashes,
4gon with circle={}{D}{C}{G}{H},
4gon with circle={red}{B}{C}{G}{F},
4gon with circle={blue}{E}{F}{G}{H},
4gon with circle={green!60!black}{A}{B}{C}{D},
4gon with circle={magenta}{A}{B}{F}{E},
4gon with circle={cyan}{A}{E}{H}{D},
}
\path foreach \p/\g in {A/-90,B/-90,C/0,D/0,E/90,F/90,G/0,H/90}{(\p)node[c]{}+(\g:2.5mm) node{$\p$}};
\end{tikzpicture}
\end{document}
```
```
\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{calc,3dtools}% https://github.com/marmotghost/tikz-3dtools
\begin{document}
\begin{tikzpicture}[3d/install view={phi=120,theta=70},line cap=butt,
line join=round,c/.style={circle,fill,inner sep=1pt},
declare function={a=3;},
y={(1cm,0)}]
\path
(a,-a,-a) coordinate (A)
(a,a,-a) coordinate (B)
(-a,a,-a) coordinate (C)
(-a,-a,-a) coordinate (D)
(a,-a,a) coordinate (E)
(a,a,a) coordinate (F)
(-a,a,a) coordinate (G)
(-a,-a,a) coordinate (H)
(0,0,0) coordinate (O)
[3d coordinate={(M)=0.5*(A) + 0.5*(H)},3d coordinate={(N)=0.5*(B) + 0.5*(G)},3d coordinate={(P)=0.5*(C) + 0.5*(H)},,3d coordinate={(Q)=0.5*(A) + 0.5*(F)} ];
\tikzset{3d/polyhedron/.cd,cr/.code n args={5}{\tikzset{3d/define orthonormal dreibein={A={(#2)},B={(#3)},C={(#4)}}}
\begin{scope}[x={(ex)},y={(ey)},z={(ez)}]
\draw[#1] ($0.25*(#2)+0.25*(#3)+0.25*(#4)+0.25*(#5)$)
circle;
\end{scope}
},4gon with circle/.style n args={5}{
after hidden/.code={
\tikzset{3d/polyhedron/cr={3d/hidden,radius=a,#1}{#2}{#3}{#4}{#5}}
},
after visible/.code={
\tikzset{3d/polyhedron/cr={3d/visible,radius=a,#1}{#2}{#3}{#4}{#5}}
},
draw face with corners={{(#2)},{(#3)},{(#4)},{(#5)}},
after hidden/.code={},after visible/.code={},
}
}
\tikzset{3d/polyhedron/.cd,O={(O)},
back/.append style={3d/hidden,fill=none},
fore/.append style={3d/visible,fill=none},
edges have complete dashes,
4gon with circle={}{D}{C}{G}{H},
4gon with circle={red}{B}{C}{G}{F},
4gon with circle={blue}{E}{F}{G}{H},
4gon with circle={green!60!black}{A}{B}{C}{D},
4gon with circle={magenta}{A}{B}{F}{E},
4gon with circle={cyan}{A}{E}{H}{D},
}
\path foreach \p/\g in {A/-90,B/-90,C/0,D/0,E/90,F/90,G/0,H/90}{(\p)node[c]{}+(\g:2.5mm) node{$\p$}};
\end{tikzpicture}
\end{document}
```How to make style of edgs of cube the same [3d/hidden]. 
`3dtools` is prepared for that, at least to some degree. You can use the `after hidden` and `after visible` hooks, which only get executed if the plane is visible or hidden. And then it makes sense to avoid repetition by defining styles that do all this for you.
```
\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{calc,3dtools}% https://github.com/marmotghost/tikz-3dtools
\begin{document}
\begin{tikzpicture}[3d/install view={phi=120,theta=70},line cap=butt,
line join=round,c/.style={circle,fill,inner sep=1pt},
declare function={a=3;}]
\path
(a,-a,-a) coordinate (A)
(a,a,-a) coordinate (B)
(-a,a,-a) coordinate (C)
(-a,-a,-a) coordinate (D)
(a,-a,a) coordinate (E)
(a,a,a) coordinate (F)
(-a,a,a) coordinate (G)
(-a,-a,a) coordinate (H)
(0,0,0) coordinate (O)
[3d coordinate={(M)=0.5*(A) + 0.5*(H)},3d coordinate={(N)=0.5*(B) + 0.5*(G)},3d coordinate={(P)=0.5*(C) + 0.5*(H)},,3d coordinate={(Q)=0.5*(A) + 0.5*(F)} ];
\tikzset{3d/polyhedron/.cd,cr/.code n args={5}{\tikzset{3d/define orthonormal dreibein={A={(#2)},B={(#3)},C={(#4)}}}
\begin{scope}[x={(ex)},y={(ey)},z={(ez)}]
\draw[#1] ($0.25*(#2)+0.25*(#3)+0.25*(#4)+0.25*(#5)$)
circle;
\end{scope}
},4gon with circle/.style n args={5}{
after hidden/.code={
\tikzset{3d/polyhedron/cr={3d/hidden,radius=a,#1}{#2}{#3}{#4}{#5}}
},
after visible/.code={
\tikzset{3d/polyhedron/cr={3d/visible,radius=a,#1}{#2}{#3}{#4}{#5}}
},
draw face with corners={{(#2)},{(#3)},{(#4)},{(#5)}},
after hidden/.code={},after visible/.code={},
}
}
\tikzset{3d/polyhedron/.cd,O={(O)},
back/.style={3d/polyhedron/complete dashes,fill=none},
fore/.style={3d/visible,fill=none},
4gon with circle={}{D}{C}{G}{H},
4gon with circle={red}{B}{C}{G}{F},
4gon with circle={blue}{E}{F}{G}{H},
4gon with circle={green!60!black}{A}{B}{C}{D},
4gon with circle={magenta}{A}{B}{F}{E},
4gon with circle={cyan}{A}{E}{H}{D},
%draw face with corners={{(D)},{(C)},{(G)},{(H)}},
%draw face with corners={{(B)},{(C)},{(G)},{(F)}},
%draw face with corners={{(E)},{(F)},{(G)},{(H)}},
%draw face with corners={{(A)},{(B)},{(C)},{(D)}},
%draw face with corners={{(A)},{(B)},{(F)},{(E)}},
%draw face with corners={{(A)},{(E)},{(H)},{(D)}}
}
\path foreach \p/\g in {A/-90,B/-90,C/0,D/0,E/90,F/90,G/0,H/90}{(\p)node[c]{}+(\g:2.5mm) node{$\p$}};
\end{tikzpicture}
\end{document}
```
I use `3dtools` to draw [here](https://topanswers.xyz/transcript?room=1851&id=100276#c100276) , I do know make style of circles automatically. How can I do that?
```
\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{calc,3dtools}% https://github.com/marmotghost/tikz-3dtools
\begin{document}
\begin{tikzpicture}[3d/install view={phi=120,theta=70},line cap=butt,line join=round,c/.style={circle,fill,inner sep=1pt},
declare function={a=3;}]
\path
(a,-a,-a) coordinate (A)
(a,a,-a) coordinate (B)
(-a,a,-a) coordinate (C)
(-a,-a,-a) coordinate (D)
(a,-a,a) coordinate (E)
(a,a,a) coordinate (F)
(-a,a,a) coordinate (G)
(-a,-a,a) coordinate (H)
(0,0,0) coordinate (O)
[3d coordinate={(M)=0.5*(A) + 0.5*(H)},3d coordinate={(N)=0.5*(B) + 0.5*(G)},3d coordinate={(P)=0.5*(C) + 0.5*(H)},,3d coordinate={(Q)=0.5*(A) + 0.5*(F)} ];
\tikzset{3d/polyhedron/.cd,O={(O)},
back/.style={3d/polyhedron/complete dashes,fill=none},
fore/.style={3d/visible,fill=none},draw face with corners={{(B)},{(C)},{(G)},{(F)}},
draw face with corners={{(D)},{(C)},{(G)},{(H)}},
draw face with corners={{(E)},{(F)},{(G)},{(H)}},
draw face with corners={{(A)},{(B)},{(C)},{(D)}},
draw face with corners={{(A)},{(B)},{(F)},{(E)}},
draw face with corners={{(A)},{(E)},{(H)},{(D)}}
}
\begin{scope}[canvas is xz plane at y=-a]
\draw[3d/hidden] (M) circle[radius=a];
\end{scope}
\begin{scope}[canvas is xz plane at y=a]
\draw[3d/visible] (N) circle[radius=a];
\end{scope}
\begin{scope}[canvas is yz plane at x=a]
\draw[3d/hidden,magenta] (P) circle[radius=a];
\end{scope}
\begin{scope}[canvas is yz plane at x=-a]
\draw[3d/visible,blue] (Q) circle[radius=a];
\end{scope}
\path foreach \p/\g in {A/-90,B/-90,C/0,D/0,E/90,F/90,G/0,H/90}{(\p)node[c]{}+(\g:2.5mm) node{$\p$}};
\end{tikzpicture}
\end{document}
```
You can use the fact that the pic installs a local frame, and use physical coordinates.
```
\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{calc,3dtools}% https://github.com/marmotghost/tikz-3dtools
\begin{document}
\pgfdeclarelayer{background}
\pgfsetlayers{background,main}
\begin{tikzpicture}[3d/install view={phi=30,theta=70,psi=0},line cap=butt,line join=round,
c/.style={circle,fill,inner sep=1pt},
declare function={r=2;h=4;}]
\path[3d/record physical components] (1,0,0) coordinate (ez') (0,1,0) coordinate (ex') (0,0,1) coordinate (ey');
\begin{scope}[x={(ex')},y={(ey')},z={(ez')}]
\path (0,0,0) coordinate (O) (0,0,h) coordinate (H);
\pic{3d/frustum={r=r,R=r,h=h}};
\begin{scope}[x={(-tdtmpex)},y={(-tdtmpey)}]
\pgfmathsetmacro{\myangle}{atan2(TDlocaly("ey'"),TDlocalx("ey'"))-90}
%\typeout{\myangle}
\fill[blue,on layer=background] (\myangle-180:r)
arc[start angle=\myangle-180,end angle=-90,radius=r]
-- ($(-tdtmpez)+(-90:r)$)
arc[start angle=-90,end angle=\myangle,radius=r]
-- (\myangle:r) -- cycle;
\draw[3d/hidden] (\myangle-180:r) -- (\myangle:r) -- ($(-tdtmpez)+(\myangle:r)$);
\draw[3d/visible] (\myangle-180:r) -- ($(-tdtmpez)+(\myangle-180:r)$) -- ($(-tdtmpez)+(\myangle:r)$);
\end{scope}
\end{scope}
\end{tikzpicture}
\end{document}
```Maybe you want to start with this?
```
\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{calc,3dtools}% https://github.com/marmotghost/tikz-3dtools
\begin{document}
\begin{tikzpicture}[3d/install view={phi=30,theta=70,psi=0},line cap=butt,line join=round,
c/.style={circle,fill,inner sep=1pt},
declare function={r=2;h=4;}]
\path (1,0,0) coordinate (ez') (0,1,0) coordinate (ex') (0,0,1) coordinate (ey');
\begin{scope}[x={(ex')},y={(ey')},z={(ez')}]
\pic{3d/frustum={r=r,R=r,h=h}};
\end{scope}
\end{tikzpicture}
\end{document}
```@marmot, re: [your answer](#a1974), I am trying to draw horizontal cylinder like this
I tried
```
\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{calc,3dtools}% https://github.com/marmotghost/tikz-3dtools
\begin{document}
\begin{tikzpicture}[3d/install view={phi=0,theta=70,psi=0},scale=1,line cap=butt,line join=round,c/.style={circle,fill,inner sep=1pt},
declare function={r=2;h=4;}]
\path
(0,0,0) coordinate (C)
(0,0,h) coordinate (T)
({r*cos(210)}, {r*sin(210)},0) coordinate (A)
({r*cos(210 + 90)}, {r*sin(210+90)},0) coordinate (B)
({r*cos(210)}, {r*sin(210)},h) coordinate (A')
({r*cos(210 + 90)}, {r*sin(210+90)},h) coordinate (B')
;
\pic{3d/frustum={r=r,R=r,h=h}};
\path foreach \p/\g in {C/-90,T/90}
{(\p)node[c]{}+(\g:2.5mm) node{$\p$}};
\draw[3d/hidden] (T) -- (C) (B) -- (C) -- (A) -- cycle;
\draw[3d/visible] (B') -- (T) -- (A') -- cycle (A) -- (A') (B) -- (B');
\end{tikzpicture}
\end{document}
```
How can I rotate the cylinder like this?
I think so. As far as I know it is not even a solved problem in many dimensions. (And, if I remember correctly, in 8 dimensions the centers of the spheres have to sit on the nodes of an E_8 root lattice to be densely packed.)
@marmot, re: [your answer](#a1974), Is this hard problem [here](https://en.wikipedia.org/wiki/Sphere_packing_in_a_cylinder)?
Very nice. Thanks.
This does such clips.
```
\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{calc,3dtools}
\begin{document}
\begin{tikzpicture}[line cap=round,line join=round,
3d/install view={phi=110,theta=70},
declare function={a=3;b=4;h=5;},c/.style={circle,fill,inner sep=1pt}]
\path
(0,0,0) coordinate (A)
(a,0,0) coordinate (B)
(0,b,0) coordinate (C)
(0,0,h) coordinate (S)
%(a/2,b/2,0) coordinate (M)
;
\path[3d/circumsphere center={A={(A)},B={(B)},C={(C)},D={(S)}}]
coordinate (I);
\pgfmathsetmacro{\myR}{sqrt(TD("(I)-(A)o(I)-(A)"))} ;
\draw[3d/screen coords] (I) circle[radius=\myR];
\path[3d/circumcircle center={A={(A)},B={(B)},C={(C)}}] coordinate (O);
\path pic{3d/circle on sphere={R=\myR,C={(I)}, P={(O)}}};
\path[3d/line through={(S) and (B) named lSB}];
\path[3d/line through={(S) and (C) named lSC}];
\path[3d/project={(A) on lSB}] coordinate (E);
\path[3d/project={(A) on lSC}] coordinate (F);
%\path[3d/circumcircle center={A={(E)},B={(B)},C={(C)}}] coordinate (M);
\path pic[draw=none]{3d circle through 3 points={%
A={(B)},B={(E)},C={(F)},center name=M}};
\pgfmathsetmacro{\myr}{tddistance("(B)","(M)")}%
\pgfmathsetmacro{\myMC}{TD("(C)-(M)")}
\pgfmathtruncatemacro{\itest}{screendepth(\myMC)<0?0:1}
\ifnum\itest=0
\begin{scope}
\clip[3d/screen coords] (I) circle[radius=\myR];
\path pic[3d/hidden]{3d circle through 3 points={%
A={(B)},B={(E)},C={(F)},center name=M}};
\end{scope}
\begin{scope}
\clip[3d/screen coords,even odd clip] (I) circle[radius=\myR]
[generous outside path];
\path pic[3d/visible]{3d circle through 3 points={%
A={(B)},B={(E)},C={(F)},center name=M}};
\end{scope}
\else
\tikzset{3d/define orthonormal dreibein={A={(B)},B={(C)},C={(F)}}}
\begin{scope}[x={(ex)},y={(ey)},z={(ez)},shift={(M)}]
\draw[3d/hidden] (B) arc[start angle=180,end angle=0,radius=\myr];
\draw[3d/visible] (B) arc[start angle=180,end angle=360,radius=\myr];
\end{scope}
\fi
\path foreach \p/\g in {A/90,B/-90,C/0,S/90,E/180,F/90,I/0,M/-90}
{(\p)node[c]{}+(\g:2.5mm) node{$\p$}};
\draw[3d/hidden] (S) -- (A) (S) --(B) (S) -- (C) (A) -- (B) -- (C) -- cycle (A) -- (E) (A) -- (F);
\end{tikzpicture}
\end{document}
```Well, yes, but then you need to compute the intersection of the circle with the sphere. I was assuming that this is `(C)` because the sphere runs throug `(C)` but what I did not check is if the intersection is on the back side, which it seems to be. If you know that this is the case, you can just use clips.
Another view 
I use GeoSpace, like this 
Maybe
```
\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{calc,3dtools}
\begin{document}
\begin{tikzpicture}[line cap=round,line join=round,
3d/install view={phi=110,theta=70},
declare function={a=3;b=4;h=5;},c/.style={circle,fill,inner sep=1pt}]
\path
(0,0,0) coordinate (A)
(a,0,0) coordinate (B)
(0,b,0) coordinate (C)
(0,0,h) coordinate (S)
%(a/2,b/2,0) coordinate (M)
;
\path[3d/circumsphere center={A={(A)},B={(B)},C={(C)},D={(S)}}]
coordinate (I);
\pgfmathsetmacro{\myR}{sqrt(TD("(I)-(A)o(I)-(A)"))} ;
\draw[3d/screen coords] (I) circle[radius=\myR];
\path[3d/circumcircle center={A={(A)},B={(B)},C={(C)}}] coordinate (O);
\path pic{3d/circle on sphere={R=\myR,C={(I)}, P={(O)}}};
\path[3d/line through={(S) and (B) named lSB}];
\path[3d/line through={(S) and (C) named lSC}];
\path[3d/project={(A) on lSB}] coordinate (E);
\path[3d/project={(A) on lSC}] coordinate (F);
\path[3d/circumcircle center={A={(A)},B={(B)},C={(C)}}] coordinate (M);
\path pic[draw=none]{3d circle through 3 points={%
A={(B)},B={(E)},C={(F)},center name=M}};
\pgfmathsetmacro{\myr}{tddistance("(B)","(M)")}%
\tikzset{3d/define orthonormal dreibein={A={(B)},B={(C)},C={(F)}}}
\begin{scope}[x={(ex)},y={(ey)},z={(ez)},shift={(M)}]
\draw[3d/hidden] (B) arc[start angle=180,end angle=0,radius=\myr];
\draw[3d/visible] (B) arc[start angle=180,end angle=360,radius=\myr];
\end{scope}
\path foreach \p/\g in {A/90,B/-90,C/0,S/90,E/180,F/90,I/0,M/-90}
{(\p)node[c]{}+(\g:2.5mm) node{$\p$}};
\draw[3d/hidden] (S) -- (A) (S) --(B) (S) -- (C) (A) -- (B) -- (C) -- cycle (A) -- (E) (A) -- (F);
\end{tikzpicture}
\end{document}
```The dashed line of the circle `BEFC` out side of the sphere incorrect. How can I fix it? 
I am trying to write answer [this question](https://tex.stackexchange.com/questions/470177/how-to-draw-a-circle-sphere-passing-through-four-points/470182#470182) by using `3dtools`.
My code
```
\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{calc,3dtools}
\begin{document}
\begin{tikzpicture}[line cap=round,line join=round,
3d/install view={phi=110,theta=70},
declare function={a=3;b=4;h=5;},c/.style={circle,fill,inner sep=1pt}]
\path
(0,0,0) coordinate (A)
(a,0,0) coordinate (B)
(0,b,0) coordinate (C)
(0,0,h) coordinate (S)
%(a/2,b/2,0) coordinate (M)
;
\path[3d/circumsphere center={A={(A)},B={(B)},C={(C)},D={(S)}}]
coordinate (I);
\pgfmathsetmacro{\myR}{sqrt(TD("(I)-(A)o(I)-(A)"))} ;
\draw[3d/screen coords] (I) circle[radius=\myR];
\path[3d/circumcircle center={A={(A)},B={(B)},C={(C)}}] coordinate (O);
\path pic{3d/circle on sphere={R=\myR,C={(I)}, P={(O)}}};
\path[3d/line through={(S) and (B) named lSB}];
\path[3d/line through={(S) and (C) named lSC}];
\path[3d/project={(A) on lSB}] coordinate (E);
\path[3d/project={(A) on lSC}] coordinate (F);
\path[3d/circumcircle center={A={(A)},B={(B)},C={(C)}}] coordinate (M);
\path pic[3d/hidden]{3d circle through 3 points={%
A={(B)},B={(E)},C={(F)},center name=M}};
\path foreach \p/\g in {A/90,B/-90,C/0,S/90,E/180,F/90,I/0,M/-90}
{(\p)node[c]{}+(\g:2.5mm) node{$\p$}};
\draw[3d/hidden] (S) -- (A) (S) --(B) (S) -- (C) (A) -- (B) -- (C) -- cycle (A) -- (E) (A) -- (F);
\end{tikzpicture}
\end{document}
```
You can also dash the line in the background.
```
\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{calc,3dtools}% https://github.com/marmotghost/tikz-3dtools
\begin{document}
\begin{tikzpicture}[line cap=round,line join=round,
3d/install view={phi=0,theta=70},
declare function={H=4;h=2.5;R=2;r=h*R/H;alpha=atan2(R,H);}]
\path (0,0,-H+h) coordinate (P)
pic[3d/visible/.style={draw=none},3d/hidden/.style={draw=none},
3d/cone/inner/.style={fill=blue!50},
3d/cone/outer/.style={fill=blue!80}]{3d/cone={h=-h,r=r}}
(0,0,0) pic{3d/cone={h=-H,r=R}}
pic{3d/circle on
sphere={C={(0,0,{-H+h+r*tan(alpha)})},P={(P)},R/.evaluated={r/cos(alpha)}}};
\end{tikzpicture}
\end{document}
```Maybe like this?
```
\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{calc,3dtools}% https://github.com/marmotghost/tikz-3dtools
\begin{document}
\begin{tikzpicture}[line cap=round,line join=round,
3d/install view={phi=0,theta=70},
declare function={H=4;h=2.5;R=2;r=h*R/H;}]
\path (0,0,-H+h) pic[%3d/visible={draw=none},3d/hidden={draw=none},
3d/cone/inner/.style={fill=blue!50},
3d/cone/outer/.style={fill=blue!80}]{3d/cone={h=-h,r=r}}
(0,0,0) pic{3d/cone={h=-H,r=R}};
\end{tikzpicture}
\end{document}
```@marmot, re: [your answer](#a1974), How about water in cone, e.g. [here](https://tex.stackexchange.com/questions/290797/draw-background-of-water-in-cone)?
It is there for a long time, just not documented.
```
\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{3dtools}% https://github.com/marmotghost/tikz-3dtools
\begin{document}
\begin{tikzpicture}[line cap=round,line join=round,
3d/install view={phi=0,theta=70}]
\path (1,2,3) coordinate (A) (4,5,6) coordinate (B) (7,8,9) coordinate (C);
\pgfmathsetmacro{\mybarycenter}{barycenter("(A),(B),(C)")}
\path (\mybarycenter) coordinate (bary);
\end{tikzpicture}
\end{document}
```Have you just added `barycenter of a list of coordinates` into `3dtools`?
Yes, there is an issue. I did not use `fpu` for one computation, so there was a `dimension too large` error. I updated the library https://github.com/marmotghost/tikz-3dtools/blob/master/tikzlibrary3dtools.code.tex.
This code does not work. I get the same result
```
\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{calc,3dtools}% https://github.com/marmotghost/tikz-3dtools
\begin{document}
\begin{tikzpicture}[line cap=round,line join=round,
3d/install view={phi=0,theta=70},
declare function={R=3;}]
\pic{3d/frustum={r=R,R=R,h=8}}; \end{tikzpicture}
\end{document}
```I tried, and cannot the result
```
\documentclass[tikz,border=3mm]{standalone}
\usetikzlibrary{calc,3dtools}% https://github.com/marmotghost/tikz-3dtools
\begin{document}
\begin{tikzpicture}[line cap=round,line join=round,
3d/install view={phi=0,theta=70},
declare function={R=3;}]
\pic{3d/frustum={r=3,R=3,h/.evaluated=2*R}};
\end{tikzpicture}
\end{document}
```
I get
