Adds a constructor for regular polygons

[gampleman]

Adds a constructor for regular polygons that are aligned with the x axis.

[ianmackenzie]

Couple small comments above but I think this looks good!

[ianmackenzie]

Argh I thought I had left a comment about API design here but it looks like it got lost somehow - I think we talked about switching to a record argument and supporting fromCircumcircle and fromIncircle as well? For the purposes of argument, what do you think about:

Polygon2d.regular :
    { numSides : Int
    , centerPoint : Point2d units coordinates
    , circumradius : Quantity Float units
    }
    -> Polygon2d units coordinates

Polygon2d.fromCircumcircle : 
    Circle2d units coordinates
    -> Int 
    -> Polygon2d units coordinates

Polygon2d.fromIncircle : 
    Circle2d units coordinates
    -> Int 
    -> Polygon2d units coordinates

[gampleman]

I believe we agreed to do the first, then leave the rest for later.

With regard to record vs. positional, I don't have any strong opinion. Since all the arguments have distinct types, I don't think the record particularly adds much value and so perhaps is just unnecessary verbose? But I could definitely swing either way.

fromCircumcircle is super straightforward and is just a wrapper around regular. It kind of makes me think you would want to have only one of these.

fromIncircle is a little trickier, so perhaps we would want to have that?

(Also I wonder if the names should be regularFromIncircle to emphasise that this is construction of regular polygons, rather than say an approximation of circle)

[ianmackenzie]

Oops, forgot to get back to this - I think I kind of like the record argument for explicitness/clarity (you can't mess up the order, but I think when reading the code it would be nice to have that confirmation that for example the Quantity value is in fact the circumradius and not the length of one side or something).

And even fromIncircle isn't that bad, I think you'd just end up doing something like

Polygon2d.regular
    { numSides = n
    , centerPoint = p
    , circumradius = r |> Quantity.divideBy (cos (pi / toFloat n))
    }

So I'm tempted to say let's just switch regular to use a record and then merge this - we can always add regularFromIncircle later if it turns out to be a common use case.

[ianmackenzie]

Looks good! OK to merge?

[gampleman]

Sure, go ahead.