Add ColourXyz::from_photon()

src/colour/colour_xyz.rs

@@ -1,6 +1,6 @@
 use crate::math::{Mat3, Vec3};
 
-use super::ColourRgbF;
+use super::{ColourRgbF, Photon};
 
 /// A CIE XYZ Colour Value
 #[derive(Clone, Debug, Default, PartialEq)]
@@ -28,6 +28,12 @@ impl ColourXyz {
         ColourXyz { values }
     }
 
+    pub fn from_photon(photon: &Photon) -> ColourXyz {
+        let mut result = Self::for_wavelength(photon.wavelength);
+        result.values *= photon.intensity;
+        result
+    }
+
     pub fn x(&self) -> f64 {
         self.values.x()
     }