Converting a static TikZ-sphere code into a command to place at arbitary locations

Question

I am wanting to use the code provided by Tom Bombadil to 3D bodies in TikZ that creates nice looking spheres, namely (with a slight adaption for showing the radius):

\draw (-1,0) arc (180:360:1cm and 0.5cm);%
\draw[dashed] (-1,0) arc (180:0:1cm and 0.5cm);%
\draw (0,1) arc (90:270:0.5cm and 1cm);%
\draw[dashed] (0,1) arc (90:-90:0.5cm and 1cm);%
\draw (0,0) circle (1cm);%
\shade[ball color=blue!10!white,opacity=0.20] (0,0) circle (1cm);%
\fill[fill=black] (0,0) circle (1pt);%
\draw[dashed] (0,0) -- node[above left]{$r$} (1,0);%

which produces:

I am having difficulty in converting this code into a command that can be placed at arbitrary locations with the radius changed to another value that then updates the dependent values. My attempts do not work when using the \the\numexpr#3/2cm etc and I am not familiar enough with tikz as yet. For instance, when using a simpler sphere code this is how my attempts at making it adaptable to different coordinates worked out:

My use case is to show 4-residue at a time spherical-searches of PDB alpha-carbon files to find helices (if all 4 alpha-carbon points lie in the sphere, high likelihood that it is in a helix region), which looks like this in my main standalone document:

How can I convert the above code into a custom command that can be placed at arbitrary locations and a modifiable radius please? Apologies that this is basic but I have been trying for half an hour and if I am struggling then perhaps others would too, would appreciate a duplicate if so (I have tried searching on here).

\documentclass[border=0pt,tikz]{standalone}
\begin{document}%
\newcommand\drawsphere[3]{%
    \draw (-1,0) arc (180:360:1cm and 0.5cm);%
    \draw[dashed] (-1,0) arc (180:0:1cm and 0.5cm);%
    \draw (0,1) arc (90:270:0.5cm and 1cm);%
    \draw[dashed] (0,1) arc (90:-90:0.5cm and 1cm);%
    \draw (0,0) circle (1cm);%
    \shade[ball color=blue!10!white,opacity=0.40] (0,0) circle (1cm);%
    \fill[fill=black] (0,0) circle (1pt);%
    \draw[dashed] (0,0) -- node[above left]{$r$} (1,0);%
}%
\begin{tikzpicture}%
\draw (-1,0) arc (180:360:1cm and 0.5cm);%
\draw[dashed] (-1,0) arc (180:0:1cm and 0.5cm);%
\draw (0,1) arc (90:270:0.5cm and 1cm);%
\draw[dashed] (0,1) arc (90:-90:0.5cm and 1cm);%
\draw (0,0) circle (1cm);%
\shade[ball color=blue!10!white,opacity=0.20] (0,0) circle (1cm);%
\fill[fill=black] (0,0) circle (1pt);%
\draw[dashed] (0,0) -- node[above left]{$r$} (1,0);%
\end{tikzpicture}
\end{document}

Answer 1

Although using pics would be better, a quick-and-dirty way:

\documentclass[border=2.7mm,tikz]{standalone}
\newcommand\drawsphere[3]{%scale, x, y
    \begin{scope}[scale=#1, shift={(#2,#3)}]
        \draw (-1,0) arc (180:360:1cm and 0.5cm);
        \draw[dashed] (-1,0) arc (180:0:1cm and 0.5cm);
        \draw (0,1) arc (90:270:0.5cm and 1cm);
        \draw[dashed] (0,1) arc (90:-90:0.5cm and 1cm);
        \draw (0,0) circle (1cm);
        \shade[ball color=blue!10!white,opacity=0.40] (0,0) circle (1cm);
        \fill[fill=black] (0,0) circle (1pt);
        \draw[dashed] (0,0) -- node[above left]{$r$} (1,0);
    \end{scope}
}
\begin{document}
\begin{tikzpicture}
    \drawsphere{1}{0}{0}
    \drawsphere{2}{2}{2}
    \drawsphere{0.5}{-1}{-1}
\end{tikzpicture}
\end{document}

As noticed by Qrrbrbirlbel, the order of the scale option is important (scaling also the shift coordinates here), and also the central dot got scaled. Maybe a better implementation is

\documentclass[border=2.7mm,tikz]{standalone}
\newcommand\drawsphere[3]{%scale, x, y
    \begin{scope}[shift={(#2,#3)}, scale=#1,
            % transform shape % if you want the "r" scaled too
        ]
        \draw (-1,0) arc (180:360:1 and 0.5);
        \draw[dashed] (-1,0) arc (180:0:1 and 0.5);
        \draw (0,1) arc (90:270:0.5 and 1);
        \draw[dashed] (0,1) arc (90:-90:0.5 and 1);
        \draw (0,0) circle (1);
        \shade[ball color=blue!10!white,opacity=0.40] (0,0) circle (1);
        \draw[dashed] (0,0) -- node[above left]{$r$} (1,0);
    \end{scope}
    \fill[black] (#2,#3) circle [radius=1pt];
}
\begin{document}
\begin{tikzpicture}
    \drawsphere{1}{0}{0}
    \drawsphere{2}{2}{2}
    \drawsphere{0.5}{-1}{-1}
\end{tikzpicture}
\end{document}

Answer 2

Here are some ways to do it with \pics, also showing work left to do. Main topics:

1. using \pic without parameter arguments
2. using \pic with parameter arguments

1. without arguments

Simply rework the \newcommand like this:

 \begin{tikzpicture}[
    sph/.pic={% ~~~ with fixed radius ~~~~~~~~~
        \draw (-1,0) arc (180:360:1cm and 0.5cm);%
        \draw[dashed] (-1,0) arc (180:0:1cm and 0.5cm);%
        \draw (0,1) arc (90:270:0.5cm and 1cm);%
        \draw[dashed] (0,1) arc (90:-90:0.5cm and 1cm);%
        \draw (0,0) circle (1cm);%
        \shade[ball color=blue!10!white,opacity=0.20] (0,0) circle (1cm);%
        \fill[fill=black] (0,0) circle (1pt);%
        \draw[dashed] (0,0) -- node[above left]{$r$} (1,0);%    
        }
    ]
...

and call it a bit like a \node, where the node here just acts as a caption:

    \pic at (0,0) {sph}; \node at (0,-1.3){1};

Now pics 1-5 show some variations of this call:

1. regular call
2. different color, rotated !! internal label "r" needs rework
3. same, made smaller >> unchanged label "r"
4. like 3, but subjecting also the label to scaling
5. enlarging it
6. miscounted for a reason == missing

with arguments

The \tikzset in the beginning shows you how to do it, while the call to use it is just --- kindly recognize passing the parameter:

\pic at (45:5) {sphr={2cm}};

Now, as you can see in picture 7 the work remains unfinished, as a bit more calculations are needed for all the arcs ... it's not just replacing 1cm by #1. Perhaps the design approach here should be thought over and improved.

I.e. a successful rework needs to replace all hardcoded:

• 1cm
• +1 coordinate
• -1 coordinate
• calculate the half of #1 to replace the 0.5cm

This can probably done better right from the start ... like:

• refactoring, like discussed here , will help, i.e. introduce the solid AND dotted half-arcs as \pic
• and certainly Qrrbirbirbel's comment should be taken into account

\documentclass[10pt,border=3mm,tikz]{standalone}
\tikzset{% ~~~ unfinished sketch for \pic taking argument(s) ~~~
    pics/sphr/.style args={#1}{% #1=radius, obviously
      code={
        \draw               (-1,0) arc (180:360:#1 and 0.5cm);%
        \draw[dashed]       (-1,0) arc (180:0:1cm and 0.5cm);%
        \draw               ( 0,1) arc (90:270:0.5cm and 1cm);%
        \draw[dashed]       ( 0,1) arc (90:-90:0.5cm and 1cm);%
        \draw               ( 0,0) circle (#1);%
        \shade[ball color=blue!10!white,opacity=0.20] 
                            ( 0,0) circle (#1);%
        \fill[fill=black]   ( 0,0) circle (1pt);%
        \draw[dashed]       ( 0,0) -- node[above left]{$r$} (1,0);%

        }
    }
}
\begin{document}
 \begin{tikzpicture}[
    sph/.pic={% ~~~ with fixed radius ~~~~~~~~~
        \draw (-1,0) arc (180:360:1cm and 0.5cm);%
        \draw[dashed] (-1,0) arc (180:0:1cm and 0.5cm);%
        \draw (0,1) arc (90:270:0.5cm and 1cm);%
        \draw[dashed] (0,1) arc (90:-90:0.5cm and 1cm);%
        \draw (0,0) circle (1cm);%
        \shade[ball color=blue!10!white,opacity=0.20] (0,0) circle (1cm);%
        \fill[fill=black] (0,0) circle (1pt);%
        \draw[dashed] (0,0) -- node[above left]{$r$} (1,0);%

        }
    ]
\pic                            at (0,0) {sph}; \node at (0,-1.3){1};
\pic[red,rotate=30]             at (5,0) {sph}; \node at (5,-1.3){2};
\pic[scale=.5]                  at (3,0) {sph}; \node at (3,-.8 ){3};
\pic[scale=.5,transform shape]  at (3,-2) {sph};\node at (3,-2.8){4};
\pic[scale=2]                   at (-2,3) {sph};\node at (-2,.6){5};

\pic                            at (45:5) {sphr={2cm}}; \node at (20:5.5){7};


\end{tikzpicture}
\end{document}