library: implement refraction

This necessitated to rework how light properties for a material were
given. A material can have either reflectivity or transparency. This
changes the parsing of materials, using a `LightProperty` structure at
its core.

This is does not implement the true Fresnel equations to take into
account the amount of reflection that an incident goes through when
encountering a transparent object.

src/core/light_properties.rs

@@ -0,0 +1,124 @@
+use super::color::LinearColor;
+use serde::Deserialize;
+
+#[derive(Debug, PartialEq, Clone, Deserialize)]
+#[serde(untagged)]
+pub enum ReflTransEnum {
+    Transparency {
+        /// The transparency coefficient.
+        #[serde(rename = "transparency")]
+        coef: f32,
+        /// The diffraction index.
+        index: f32,
+    },
+    Reflectivity {
+        /// The reflectivity coefficient.
+        #[serde(rename = "reflectivity")]
+        coef: f32,
+    },
+}
+
+/// A structure holding all the physical proprerties relating to light at a point.
+#[derive(Debug, PartialEq, Clone, Deserialize)]
+pub struct LightProperties {
+    /// The diffuse component.
+    pub diffuse: LinearColor,
+    /// The specular component.
+    pub specular: LinearColor,
+    /// The transparency or reflectivity properties.
+    #[serde(flatten)]
+    pub refl_trans: Option<ReflTransEnum>,
+}
+
+impl LightProperties {
+    pub fn new(
+        diffuse: LinearColor,
+        specular: LinearColor,
+        refl_trans: Option<ReflTransEnum>,
+    ) -> Self {
+        LightProperties {
+            diffuse,
+            specular,
+            refl_trans,
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn new_works() {
+        let diffuse = LinearColor::new(0.25, 0.5, 1.);
+        let specular = LinearColor::new(0.75, 0.375, 0.125);
+        let refl_trans = Some(ReflTransEnum::Reflectivity { coef: 0.5 });
+        let properties =
+            LightProperties::new(diffuse.clone(), specular.clone(), refl_trans.clone());
+        assert_eq!(
+            properties,
+            LightProperties {
+                diffuse,
+                specular,
+                refl_trans,
+            }
+        )
+    }
+
+    #[test]
+    fn deserialization_without_refl_trans_works() {
+        let yaml = r#"
+            diffuse: {r: 1.0, g: 0.5, b: 0.25}
+            specular: {r: 0.25, g: 0.125, b: 0.75}
+        "#;
+        let properties: LightProperties = serde_yaml::from_str(yaml).unwrap();
+        assert_eq!(
+            properties,
+            LightProperties::new(
+                LinearColor::new(1., 0.5, 0.25),
+                LinearColor::new(0.25, 0.125, 0.75),
+                None
+            )
+        )
+    }
+
+    #[test]
+    fn deserialization_with_reflection_works() {
+        let yaml = r#"
+            diffuse: {r: 1.0, g: 0.5, b: 0.25}
+            specular: {r: 0.25, g: 0.125, b: 0.75}
+            transparency: 0.5
+            index: 1.5
+        "#;
+        let properties: LightProperties = serde_yaml::from_str(yaml).unwrap();
+        assert_eq!(
+            properties,
+            LightProperties::new(
+                LinearColor::new(1., 0.5, 0.25),
+                LinearColor::new(0.25, 0.125, 0.75),
+                Some(ReflTransEnum::Transparency {
+                    coef: 0.5,
+                    index: 1.5
+                })
+            )
+        )
+    }
+
+    #[test]
+    fn deserialization_with_transparency_works() {
+        let yaml = r#"
+            diffuse: {r: 1.0, g: 0.5, b: 0.25}
+            specular: {r: 0.25, g: 0.125, b: 0.75}
+            reflectivity: 0.25
+        "#;
+        let properties: LightProperties = serde_yaml::from_str(yaml).unwrap();
+        assert_eq!(
+            properties,
+            LightProperties::new(
+                LinearColor::new(1., 0.5, 0.25),
+                LinearColor::new(0.25, 0.125, 0.75),
+                Some(ReflTransEnum::Reflectivity { coef: 0.25 })
+            )
+        )
+    }
+}

src/core/mod.rs

@@ -6,3 +6,6 @@ pub use color::*;
 
 pub mod film;
 pub use film::*;
+
+pub mod light_properties;
+pub use light_properties::*;