library: light: add luminance to Light trait

pathtracer/src/light/ambient_light.rs

@@ -27,6 +27,10 @@ impl AmbientLight {
 
 impl Light for AmbientLight {
     fn illumination(&self, _: &Point) -> LinearColor {
+        self.luminance()
+    }
+
+    fn luminance(&self) -> LinearColor {
         self.color.clone()
     }
 }

pathtracer/src/light/directional_light.rs

@@ -34,6 +34,10 @@ impl DirectionalLight {
 
 impl Light for DirectionalLight {
     fn illumination(&self, _: &Point) -> LinearColor {
+        self.luminance()
+    }
+
+    fn luminance(&self) -> LinearColor {
         self.color.clone()
     }
 }

pathtracer/src/light/mod.rs

@@ -9,6 +9,9 @@ use nalgebra::Unit;
 pub trait Light: std::fmt::Debug {
     /// Get the illumination of that light on that point.
     fn illumination(&self, point: &Point) -> LinearColor;
+
+    /// Get the raw luminance of that light
+    fn luminance(&self) -> LinearColor;
 }
 
 /// Represent a light which has an abstract position in the scene being rendered.

pathtracer/src/light/point_light.rs

@@ -36,7 +36,11 @@ impl PointLight {
 impl Light for PointLight {
     fn illumination(&self, point: &Point) -> LinearColor {
         let dist = (self.position - point).norm();
-        self.color.clone() / dist
+        self.luminance() / dist
+    }
+
+    fn luminance(&self) -> LinearColor {
+        self.color.clone()
     }
 }
 

pathtracer/src/light/spot_light.rs

@@ -54,11 +54,15 @@ impl Light for SpotLight {
         let delt = point - self.position;
         let cos = self.direction.dot(&delt.normalize());
         if cos >= self.cosine_value {
-            self.color.clone() / delt.norm_squared()
+            self.luminance() / delt.norm_squared()
         } else {
             LinearColor::black()
         }
     }
+
+    fn luminance(&self) -> LinearColor {
+        self.color.clone()
+    }
 }
 
 impl SpatialLight for SpotLight {