Document distribution uniformity, fix `Rotation2` distribution

Also tweak UnitComplex distribution for consistency

CHANGELOG.md

@@ -6,7 +6,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [0.16.0] - WIP
 ## Modified
-  * Adjust `UnitQuaternion`s and `Rotation3`s generated from the `Standard` distribution to be uniformly distributed.
+  * Adjust `UnitQuaternion`s, `Rotation3`s, and `Rotation2`s generated from the `Standard` distribution to be uniformly
+    distributed.
 ### Added
   * Add construction of a `Point` from an array by implementing the `From` trait.
   * Add support for generating uniformly distributed random unit column vectors using the `Standard` distribution.

src/base/construction.rs

@@ -507,6 +507,7 @@ where
     DefaultAllocator: Allocator<N, D>,
     StandardNormal: Distribution<N>,
 {
+    /// Generate a uniformly distributed random unit vector.
     #[inline]
     fn sample<'a, G: Rng + ?Sized>(&self, rng: &'a mut G) -> Unit<VectorN<N, D>> {
         Unit::new_normalize(VectorN::from_distribution_generic(D::name(), U1, &mut StandardNormal, rng))

src/geometry/quaternion_construction.rs

@@ -415,6 +415,7 @@ impl<N: Real> Distribution<UnitQuaternion<N>> for Standard
 where
     OpenClosed01: Distribution<N>,
 {
+    /// Generate a uniformly distributed random rotation quaternion.
     #[inline]
     fn sample<'a, R: Rng + ?Sized>(&self, rng: &'a mut R) -> UnitQuaternion<N> {
         // Ken Shoemake's Subgroup Algorithm

src/geometry/rotation_specialization.rs

@@ -100,11 +100,12 @@ impl<N: Real> Rotation2<N> {
 
 impl<N: Real> Distribution<Rotation2<N>> for Standard
 where
-    Standard: Distribution<N>,
+    OpenClosed01: Distribution<N>,
 {
+    /// Generate a uniformly distributed random rotation.
     #[inline]
     fn sample<'a, R: Rng + ?Sized>(&self, rng: &'a mut R) -> Rotation2<N> {
-        Rotation2::new(rng.gen())
+        Rotation2::new(rng.sample(OpenClosed01) * N::two_pi())
     }
 }
 
@@ -386,6 +387,7 @@ impl<N: Real> Distribution<Rotation3<N>> for Standard
 where
     OpenClosed01: Distribution<N>,
 {
+    /// Generate a uniformly distributed random rotation.
     #[inline]
     fn sample<'a, R: Rng + ?Sized>(&self, rng: &mut R) -> Rotation3<N> {
         // James Arvo.

src/geometry/unit_complex_construction.rs

@@ -3,7 +3,7 @@ use quickcheck::{Arbitrary, Gen};
 
 use num::One;
 use num_complex::Complex;
-use rand::distributions::{Distribution, Standard};
+use rand::distributions::{Distribution, Standard, OpenClosed01};
 use rand::Rng;
 
 use alga::general::Real;
@@ -153,11 +153,12 @@ impl<N: Real> One for UnitComplex<N> {
 
 impl<N: Real> Distribution<UnitComplex<N>> for Standard
 where
-    Standard: Distribution<N>,
+    OpenClosed01: Distribution<N>,
 {
+    /// Generate a uniformly distributed random `UnitComplex`.
     #[inline]
     fn sample<'a, R: Rng + ?Sized>(&self, rng: &mut R) -> UnitComplex<N> {
-        UnitComplex::from_angle(rng.gen() * N::two_pi())
+        UnitComplex::from_angle(rng.sample(OpenClosed01) * N::two_pi())
     }
 }