[swift-evolution] [Pitch] Angle Type

[Kelvin Ma]

This could work, but you’re also giving up all the nice Numeric and
FloatingPoint conformances when you use this,, all of a sudden adding two
angles together isn’t let γ = α + β, it’s γ = Angle.radians(α.radians +
β.radians). just no. at the risk of blowing up the scope of this idea,
dedicated Angle types also begs for generic trigonometric functions like
Angle.sin(_:) and Angle.cos(_:). i proposed that a while back and even
tried implementing it but fast trig evaluation doesn’t genericize well
since it relies a lot on rsqrt-style magic constants

also, why are radians(_:) and degrees(_:) static functions? i really only
use static constructors for initializers that have side effects

On Sun, Jan 14, 2018 at 6:36 AM, Karl Wagner <razielim at gmail.com> wrote:

>
>
> On 14. Jan 2018, at 09:51, Taylor Swift via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> I do a lot of geometry and spherical-related work and i have never found
> an Angle type to be worth having. Always use radians. It’s what sin() and
> cos() take, it’s what graphics APIs like Cairo expect, it’s what graphics
> formats like SVG use. plus,, do you *really* want to be case-branching on
> every angle value? that really adds up when you’re converting 100,000s of
> lat-long pairs to cartesian.
>
>
> You can do it without case-branching. I too have an Angle type; this is
> what I use:
>
> public struct Angle<T: FloatingPoint> {
>   public var radians: T
>   public var degrees: T {
>     return (radians / .pi) * 180
>   }
>
>   public static func radians(_ rads: T) -> Angle {
>     return Angle(radians: rads)
>   }
>   public static func degrees(_ degs: T) -> Angle {
>     return Angle(radians: (degs / 180) * .pi)
>   }
> }
>
> If you ask for “radians” (like most low-level trig code will), you just
> get the stored property. The conversion “overhead” is only done at
> construction time, so it makes a convenient parameter/return value.
>
> - Karl
>
>
> On Jan 14, 2018, at 12:04 AM, BJ Homer via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> An Angle type already exists in Foundation; see Measurement<UnitAngle>.
> You could add some convenience methods in an extension pretty easily.
>
> import Foundation
>
> typealias Angle = Measurement<UnitAngle>
>
> extension Measurement where UnitType == UnitAngle {
>     var sine: Double {
>         let radians = self.converted(to: .radians).value
>         return sin(radians)
>     }
>
>
>     static var threeQuarterTurn: Angle {
>         return Angle(value: 0.75, unit: .revolutions)
>     }
> }
>
> let x = Angle.threeQuarterTurn
> x.sine // -1
>
>
> -BJ
>
>
> On Jan 13, 2018, at 9:31 PM, Erica Sadun via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> I would like to see a full Geometry implementation but I don't think it
> should be part of the standard library.
>
> I've kicked around some ideas here:
>
> * https://gist.github.com/erica/8cb4b21cf0c429828fad1d8ad459b71b
> * https://gist.github.com/erica/ee06008202c9fed699bfa6254c42c721
>
> and
>
> * https://github.com/erica/SwiftGeometry
>
> On Jan 13, 2018, at 7:49 PM, Jonathan Hull via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> Hi Evolution,
>
> I would *really* like to see Swift gain an Angle type in the standard
> library.  Every time I have to deal with an angle in an api, I have to go
> figure out the conventions for that call.  Is it in degrees? Is it in
> radians?  What if it is in radians, but I want to think about it in degrees?
>
> I ended up writing an Angle type for my own code a few years back, and I
> have to say it is really wonderful.  It has greatly simplified my graphics
> work.  It takes a lot of mental load off of my brain when dealing with
> Angles.
>
> I can of course initialize it either as degrees or radians (or
> revolutions), but I can also just say things like ‘.threeQuarterTurn’, and
> then I can get the value back out in whatever format I like.  There are
> also useful additions that let me normalize the angle to different ranges
> and which let me snap to the nearest multiple of an angle. Both of these
> are enormously useful for user facing features.  I can also do math on
> angles in a way that makes geometric sense for angles.  It is also really
> useful for interacting with CGVectors in intelligent ways.
>
> Using Doubles or CGFloats to represent angles everywhere is just
> semantically wrong IMHO, and it stops us from adding all of these
> angle-specific niceties.
>
> Happy to provide code if there is interest…
>
> Thanks,
> Jon
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