From 9ec3525b1550f108179390ef23269419fbfff9df Mon Sep 17 00:00:00 2001
From: Matthew Gordon <matthew.scott.gordon@gmail.com>
Date: Sun, 3 Oct 2021 11:01:34 -0400
Subject: [PATCH] Add random_distributions::UnitDisc

---
 src/random_distributions/mod.rs       |  3 ++
 src/random_distributions/unit_disc.rs | 49 +++++++++++++++++++++++++++
 2 files changed, 52 insertions(+)
 create mode 100644 src/random_distributions/unit_disc.rs

diff --git a/src/random_distributions/mod.rs b/src/random_distributions/mod.rs
index 0df18b3..d74beca 100644
--- a/src/random_distributions/mod.rs
+++ b/src/random_distributions/mod.rs
@@ -1,6 +1,9 @@
 mod uniform_square;
 pub use uniform_square::UniformSquare;
 
+mod unit_disc;
+pub use unit_disc::UnitDisc;
+
 pub trait RandomDistribution<T> {
     fn value(&self) -> T;
 }
diff --git a/src/random_distributions/unit_disc.rs b/src/random_distributions/unit_disc.rs
new file mode 100644
index 0000000..84ce12c
--- /dev/null
+++ b/src/random_distributions/unit_disc.rs
@@ -0,0 +1,49 @@
+use std::f64::consts::PI;
+
+use crate::math::Vec2;
+
+use super::{RandomDistribution, UniformSquare};
+
+#[derive(Debug)]
+pub struct UnitDisc {
+    square_distribution: UniformSquare,
+}
+
+impl UnitDisc {
+    pub fn new() -> UnitDisc {
+        let square_distribution = UniformSquare::new(Vec2::new(-1.0, -1.0), 2.0);
+        UnitDisc {
+            square_distribution,
+        }
+    }
+}
+
+impl RandomDistribution<Vec2> for UnitDisc {
+    fn value(&self) -> Vec2 {
+        let offset = self.square_distribution.value();
+        if offset.x() == 0.0 && offset.y() == 0.0 {
+            offset
+        } else {
+            let (radius, angle) = if offset.x().abs() > offset.y().abs() {
+                (offset.x(), (PI / 4.0) * offset.y() / offset.x())
+            } else {
+                (offset.y(), PI / 2.0 - (PI / 4.0) * offset.x() / offset.y())
+            };
+            Vec2::new(angle.cos(), angle.sin()) * radius
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn print_values() {
+        let target = UnitDisc::new();
+        for _ in 0..1000 {
+            let value = target.value();
+            println!("{}, {}", value.x(), value.y());
+        }
+    }
+}