From ed224b18cb8b329cbfffce91a35c815fa6ff019b Mon Sep 17 00:00:00 2001
From: Matthew Gordon <matthew.scott.gordon@gmail.com>
Date: Thu, 7 Oct 2021 11:23:46 -0400
Subject: [PATCH] Add random_distributions::LinearWeighted

---
 src/integrators/simple_random_integrator.rs |  2 +-
 src/integrators/whitted_integrator.rs       |  2 +-
 src/random_distributions/linear_weighted.rs | 67 +++++++++++++++++++++
 src/random_distributions/mod.rs             |  3 +
 4 files changed, 72 insertions(+), 2 deletions(-)
 create mode 100644 src/random_distributions/linear_weighted.rs

diff --git a/src/integrators/simple_random_integrator.rs b/src/integrators/simple_random_integrator.rs
index 89db98d..b24863c 100644
--- a/src/integrators/simple_random_integrator.rs
+++ b/src/integrators/simple_random_integrator.rs
@@ -1,6 +1,6 @@
-use crate::math::Vec3;
 use crate::colour::{ColourRgbF, Photon, Spectrum};
 use crate::materials::MaterialSampleResult;
+use crate::math::Vec3;
 use crate::raycasting::{IntersectionInfo, Ray};
 use crate::sampler::Sampler;
 use crate::util::algebra_utils::try_change_of_basis_matrix;
diff --git a/src/integrators/whitted_integrator.rs b/src/integrators/whitted_integrator.rs
index c6e0198..3875c26 100644
--- a/src/integrators/whitted_integrator.rs
+++ b/src/integrators/whitted_integrator.rs
@@ -1,6 +1,6 @@
-use crate::math::Vec3;
 use crate::colour::{Photon, Spectrum};
 use crate::materials::MaterialSampleResult;
+use crate::math::Vec3;
 use crate::raycasting::{IntersectionInfo, Ray};
 use crate::sampler::Sampler;
 use crate::util::algebra_utils::try_change_of_basis_matrix;
diff --git a/src/random_distributions/linear_weighted.rs b/src/random_distributions/linear_weighted.rs
new file mode 100644
index 0000000..705d990
--- /dev/null
+++ b/src/random_distributions/linear_weighted.rs
@@ -0,0 +1,67 @@
+use rand::distributions::Open01;
+use rand::{thread_rng, Rng};
+
+use super::RandomDistribution;
+
+pub struct LinearWeighted {
+    max_value: f64,
+}
+
+impl LinearWeighted {
+    pub fn new(max_value: f64) -> LinearWeighted {
+        LinearWeighted { max_value }
+    }
+}
+
+impl RandomDistribution<f64> for LinearWeighted {
+    fn value(&self) -> f64 {
+        let mut rng = thread_rng();
+        rng.sample::<f64, _>(Open01).sqrt() * self.max_value
+    }
+
+    fn pdf(&self, value: f64) -> f64 {
+        2.0 * value / (self.max_value * self.max_value)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    #[ignore]
+    fn print_values() {
+        let target = LinearWeighted::new(2.0);
+        for _ in 0..1000 {
+            let value = target.value();
+            println!("{}", value);
+        }
+    }
+
+    #[test]
+    #[ignore]
+    fn print_buckets() {
+        let mut buckets = [0; 20];
+        let target = LinearWeighted::new(20.0);
+        for _ in 0..10000 {
+            let value = target.value();
+            let i = value as usize;
+            buckets[i] += 1;
+        }
+        for count in buckets {
+            println!("{}", count);
+        }
+    }
+
+    #[test]
+    #[ignore]
+    fn integral_is_near_area() {
+        let target = LinearWeighted::new(2.0);
+        let integral = (0..100000)
+            .map(|_| target.value())
+            .map(|value| 1.0 / target.pdf(value))
+            .sum::<f64>()
+            / 100000.0;
+        println!("Area: {}\nIntegral: {}", 2.0, integral);
+    }
+}
diff --git a/src/random_distributions/mod.rs b/src/random_distributions/mod.rs
index b63ccd8..b259ca3 100644
--- a/src/random_distributions/mod.rs
+++ b/src/random_distributions/mod.rs
@@ -10,6 +10,9 @@ pub use uniform_hemisphere::UniformHemisphere;
 mod cosine_weighted_hemisphere;
 pub use cosine_weighted_hemisphere::CosineWeightedHemisphere;
 
+mod linear_weighted;
+pub use linear_weighted::LinearWeighted;
+
 pub trait RandomDistribution<T> {
     fn value(&self) -> T;
     fn pdf(&self, value: T) -> f64;