From 2088877bd26899851fde1d5ea11ce3db1ab1fca4 Mon Sep 17 00:00:00 2001
From: Bruno BELANYI <brunobelanyi@gmail.com>
Date: Mon, 16 Mar 2020 18:35:01 +0100
Subject: [PATCH] library: light: add SpotLight implementation

---
 src/light/mod.rs        |   3 +
 src/light/spot_light.rs | 160 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 163 insertions(+)
 create mode 100644 src/light/spot_light.rs

diff --git a/src/light/mod.rs b/src/light/mod.rs
index d2c1d40..2096101 100644
--- a/src/light/mod.rs
+++ b/src/light/mod.rs
@@ -21,3 +21,6 @@ pub use directional_light::*;
 
 pub mod point_light;
 pub use point_light::*;
+
+pub mod spot_light;
+pub use spot_light::*;
diff --git a/src/light/spot_light.rs b/src/light/spot_light.rs
new file mode 100644
index 0000000..170ccce
--- /dev/null
+++ b/src/light/spot_light.rs
@@ -0,0 +1,160 @@
+use super::super::core::LinearColor;
+use super::super::{Point, Vector};
+use super::{Light, SpatialLight};
+
+/// Represent a light emanating from a directed light-source, outputting rays in a cone.
+/// The illumination cone cannot have an FOV over 180°.
+#[derive(Debug, PartialEq)]
+pub struct SpotLight {
+    position: Point,
+    direction: Vector,
+    cosine_value: f32,
+    color: LinearColor,
+}
+
+impl SpotLight {
+    /// Construct a SpotLight with the given FOV in radian.
+    pub fn radians_new(
+        position: Point,
+        direction: Vector,
+        fov_rad: f32,
+        color: LinearColor,
+    ) -> Self {
+        SpotLight {
+            position,
+            direction,
+            cosine_value: (fov_rad / 2.).cos(),
+            color,
+        }
+    }
+
+    /// Construct a SpotLight with the given FOV in degrees.
+    pub fn degrees_new(
+        position: Point,
+        direction: Vector,
+        fov_deg: f32,
+        color: LinearColor,
+    ) -> Self {
+        SpotLight {
+            position,
+            direction,
+            cosine_value: (std::f32::consts::PI * fov_deg / 360.).cos(),
+            color,
+        }
+    }
+}
+
+impl Light for SpotLight {
+    fn illumination(&self, point: &Point) -> LinearColor {
+        let delt = point - self.position;
+        let cos = self.direction.dot(&delt.normalize());
+        if cos >= self.cosine_value {
+            self.color.clone() / delt.norm_squared()
+        } else {
+            LinearColor::black()
+        }
+    }
+}
+
+impl SpatialLight for SpotLight {
+    fn to_source(&self, point: &Point) -> (Vector, f32) {
+        let delt = self.position - point;
+        let dist = delt.norm();
+        (delt.normalize(), dist)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn radian_new_works() {
+        let light = SpotLight::radians_new(
+            Point::origin(),
+            Vector::new(1., 0., 0.),
+            std::f32::consts::PI / 2.,
+            LinearColor::new(1., 1., 1.),
+        );
+        // The FOV is 90°, therefore the angle to the direction is 45° [= PI / 4]
+        let calculated_cosine_value = (std::f32::consts::PI / 4.).cos();
+        assert_eq!(
+            light,
+            SpotLight {
+                position: Point::origin(),
+                direction: Vector::new(1., 0., 0.),
+                cosine_value: calculated_cosine_value,
+                color: LinearColor::new(1., 1., 1.),
+            }
+        );
+        // Checking this way because of rounding issues...
+        assert!((calculated_cosine_value - f32::sqrt(2.) / 2.).abs() < 1e-5)
+    }
+
+    #[test]
+    fn degrees_new_works() {
+        let light = SpotLight::degrees_new(
+            Point::origin(),
+            Vector::new(1., 0., 0.),
+            60.,
+            LinearColor::new(1., 1., 1.),
+        );
+        let calculated_cosine_value = (std::f32::consts::PI * 60. / 360.).cos();
+        assert_eq!(
+            light,
+            SpotLight {
+                position: Point::origin(),
+                direction: Vector::new(1., 0., 0.),
+                cosine_value: calculated_cosine_value,
+                color: LinearColor::new(1., 1., 1.),
+            }
+        );
+        // Checking this way because of rounding issues...
+        assert!((calculated_cosine_value - f32::sqrt(3.) / 2.).abs() < 1e-5)
+    }
+
+    fn simple_light() -> impl SpatialLight {
+        SpotLight::degrees_new(
+            Point::origin(),
+            Vector::new(1., 0., 0.),
+            90.,
+            LinearColor::new(1., 1., 1.),
+        )
+    }
+
+    #[test]
+    fn illumination_in_axis_works() {
+        let light = simple_light();
+        let lum = light.illumination(&Point::new(1., 0., 0.));
+        assert_eq!(lum, LinearColor::new(1., 1., 1.))
+    }
+
+    #[test]
+    fn illumination_on_limit_works_1() {
+        let light = simple_light();
+        let lum = light.illumination(&Point::new(1., 1., 0.));
+        assert_eq!(lum, LinearColor::new(0.5, 0.5, 0.5))
+    }
+
+    #[test]
+    fn illumination_on_limit_works_2() {
+        let light = simple_light();
+        let lum = light.illumination(&Point::new(1., 0., 1.));
+        assert_eq!(lum, LinearColor::new(0.5, 0.5, 0.5))
+    }
+
+    #[test]
+    fn illumination_out_of_ray_works() {
+        let light = simple_light();
+        let lum = light.illumination(&Point::new(1., 1., 1.));
+        assert_eq!(lum, LinearColor::new(0., 0., 0.))
+    }
+
+    #[test]
+    fn to_source_is_correct() {
+        let light = simple_light();
+        let ans = light.to_source(&Point::new(1., 0., 0.));
+        let expected = (Vector::new(-1., 0., 0.), 1.);
+        assert_eq!(ans, expected);
+    }
+}