Add UniformHemisphere random distribution

src/random_distributions/mod.rs

@@ -4,6 +4,9 @@ pub use uniform_square::UniformSquare;
 mod unit_disc;
 pub use unit_disc::UnitDisc;
 
+mod uniform_hemisphere;
+pub use uniform_hemisphere::UniformHemisphere;
+
 pub trait RandomDistribution<T> {
     fn value(&self) -> T;
 }

src/random_distributions/uniform_hemisphere.rs

@@ -0,0 +1,48 @@
+use rand::distributions::{Open01, OpenClosed01};
+use rand::{thread_rng, Rng};
+
+use crate::math::Vec3;
+
+use super::RandomDistribution;
+
+pub struct UniformHemisphere {}
+
+impl UniformHemisphere {
+    pub fn new() -> UniformHemisphere {
+        UniformHemisphere {}
+    }
+}
+
+impl RandomDistribution<Vec3> for UniformHemisphere {
+    fn value(&self) -> Vec3 {
+        let mut rng = thread_rng();
+        let mut result = Vec3::new(
+            2.0 * rng.sample::<f64, _>(Open01) - 1.0,
+            2.0 * rng.sample::<f64, _>(Open01) - 1.0,
+            rng.sample::<f64, _>(OpenClosed01),
+        );
+        while result.norm_squared() > 1.0 {
+            result = Vec3::new(
+                2.0 * rng.sample::<f64, _>(Open01) - 1.0,
+                2.0 * rng.sample::<f64, _>(Open01) - 1.0,
+                rng.sample::<f64, _>(OpenClosed01),
+            );
+        }
+        result.normalize()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    #[ignore]
+    fn print_values() {
+        let target = UniformHemisphere::new();
+        for _ in 0..1000 {
+            let value = target.value();
+            println!("{}, {}, {}", value.x(), value.y(), value.z());
+        }
+    }
+}