# [NTG-context] atan2 function

Thangalin thangalin at gmail.com
Sat Oct 15 01:09:41 CEST 2022

```That's certainly tighter, thank you, Alan.

Would making the conditional part of the API be useful to others?

Cheers!

On Fri, Oct 14, 2022 at 3:42 PM Alan Braslau <alan.braslau at icloud.com> wrote:
>
> On Fri, 14 Oct 2022 11:59:49 -0700
> Thangalin <thangalin at gmail.com> wrote:
>
> > I don't think an atantwo is needed. I *thought* I had read somewhere
> > that atan( y, x ) was equivalent to calling atan2 in Lua. Ensuring
> > there's no breakage when x == y would be nice, though. It was a little
> > surprising to see angle return degrees rather than radians, but it
> > does simplify my code:
> >
> >       dc := vbc - vac;
> >       dr := vbr - var;
> >       vi := 0;
> >
> >       if not( dc == dr ):
> >         vi := round( angle( dc, dr ) / 60 );
> >       fi;
> >
> >       % Compute the direction towards the first segment (to vertex of
> > an edge). vangle := vi * 60 * pi / 180;
> >
> > Even simpler would be:
> >
> >       dc := vbc - vac;
> >       dr := vbr - var;
> >       vi := round( angle( dc, dr ) / 60 ); % returns 0 when dc == dr
> >
> >       % Compute the direction towards the first segment (to vertex of
> > an edge). vangle := vi * 60 * pi / 180;
> >
> > Or accepting a third argument as the return value in the special case:
> >
> >       vi := round( angle( dc, dr, 0 ) / 60 ); % returns 0 when dc ==
> > dr
> >
> > Cheers!
>
> vi := if (dc = dr) : 0 else : round (angle(dc,dr)/60) fi ;
>
> Alan
```