Perfect reflection, and Lambert, for spheres and planes (#1)

RayTracing.Test/TestSphere.fs

@@ -0,0 +1,45 @@
+namespace RayTracing.Test
+
+open RayTracing
+open NUnit.Framework
+open FsCheck
+
+[<TestFixture>]
+module TestSphere =
+
+    [<Test>]
+    let ``Point at distance r from centre lies on sphere`` () =
+        let property (centre : Point<float>, radius : float, point : Point<float>) : bool =
+            let radius = abs radius
+            let sphere = Sphere.make Num.float (SphereStyle.PureReflection (1.0, Colour.White)) centre radius
+            Sphere.liesOn Num.float point sphere
+
+
+        let gen : Gen<Point<float> * float * Point<float>> =
+            gen {
+                let! centre = TestUtils.pointGen
+                let! radius = Arb.generate<NormalFloat> |> Gen.map NormalFloat.op_Explicit
+                let! theta =
+                    Arb.generate<NormalFloat>
+                    |> Gen.map NormalFloat.op_Explicit
+                    |> Gen.map Radian
+                let! phi =
+                    Arb.generate<NormalFloat>
+                    |> Gen.map NormalFloat.op_Explicit
+                    |> Gen.map Radian
+
+                let surfacePoint =
+                    [|
+                        radius * Num.float.Cos phi * Num.float.Sin theta
+                        radius * Num.float.Sin phi * Num.float.Sin theta
+                        radius * Num.float.Cos theta
+                    |]
+                    |> Point
+                    |> Point.difference Num.float centre
+                    |> fun (Vector v) -> Point v
+                return centre, radius, surfacePoint
+            }
+
+        property
+        |> Prop.forAll (Arb.fromGen gen)
+        |> Check.QuickThrowOnFailure