Add some comments about random variates

src/geometry/orthographic.rs

@@ -691,6 +691,7 @@ impl<N: RealField> Distribution<Orthographic3<N>> for Standard
 where
     Standard: Distribution<N>,
 {
+    /// Generate an arbitrary random variate for testing purposes.
     fn sample<R: Rng + ?Sized>(&self, r: &mut R) -> Orthographic3<N> {
         use crate::base::helper;
         let left = r.gen();

src/geometry/perspective.rs

@@ -275,6 +275,7 @@ impl<N: RealField> Distribution<Perspective3<N>> for Standard
 where
     Standard: Distribution<N>,
 {
+    /// Generate an arbitrary random variate for testing purposes.
     fn sample<'a, R: Rng + ?Sized>(&self, r: &'a mut R) -> Perspective3<N> {
         use crate::base::helper;
         let znear = r.gen();

src/geometry/point_construction.rs

@@ -164,6 +164,7 @@ where
     DefaultAllocator: Allocator<N, D>,
     Standard: Distribution<N>,
 {
+     /// Generate a `Point` where each coordinate is an independent variate from `[0, 1)`.
     #[inline]
     fn sample<'a, G: Rng + ?Sized>(&self, rng: &mut G) -> Point<N, D> {
         Point::from(rng.gen::<VectorN<N, D>>())

src/geometry/similarity_construction.rs

@@ -69,6 +69,7 @@ where
     DefaultAllocator: Allocator<N, D>,
     Standard: Distribution<N> + Distribution<R>,
 {
+    /// Generate an arbitrary random variate for testing purposes.
     #[inline]
     fn sample<'a, G: Rng + ?Sized>(&self, rng: &mut G) -> Similarity<N, D, R> {
         let mut s = rng.gen();

src/geometry/translation_construction.rs

@@ -78,6 +78,7 @@ where
     DefaultAllocator: Allocator<N, D>,
     Standard: Distribution<N>,
 {
+    /// Generate an arbitrary random variate for testing purposes.
     #[inline]
     fn sample<'a, G: Rng + ?Sized>(&self, rng: &'a mut G) -> Translation<N, D> {
         Translation::from(rng.gen::<VectorN<N, D>>())

tests/core/helper.rs

@@ -33,6 +33,8 @@ where
 
 // This is a wrapper similar to RandComplex, but for non-complex.
 // This exists only to make generic tests easier to write.
+//
+// Generates variates in the range [0, 1).
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 pub struct RandScalar<N>(pub N);