feat: add HitableTrait::centroid method

clovers/src/bvh/hitable_trait.rs

@@ -129,4 +129,9 @@ impl<'scene> HitableTrait for BVHNode<'scene> {
             }
         }
     }
+
+    // TODO: remove?
+    fn centroid(&self) -> Position {
+        self.bounding_box.centroid()
+    }
 }

clovers/src/hitable.rs

@@ -11,7 +11,7 @@ use crate::{
     objects::{Boxy, ConstantMedium, MovingSphere, Quad, RotateY, Sphere, Translate, Triangle},
     ray::Ray,
     wavelength::Wavelength,
-    Direction, Displacement, Float, HitRecord, Position,
+    Direction, Displacement, Float, HitRecord, Position, Vec3,
 };
 
 use enum_dispatch::enum_dispatch;
@@ -70,6 +70,10 @@ impl HitableTrait for Empty {
     ) -> Float {
         0.0
     }
+
+    fn centroid(&self) -> Position {
+        Vec3::new(0.0, 0.0, 0.0)
+    }
 }
 
 #[enum_dispatch]
@@ -107,6 +111,10 @@ pub trait HitableTrait {
             "HitableTrait::random called for a Hitable that has no implementation for it!"
         );
     }
+
+    /// Returns the center point of the hitable
+    #[must_use]
+    fn centroid(&self) -> Position;
 }
 
 /// Returns a tuple of `(front_face, normal)`. Used in lieu of `set_face_normal` in the Ray Tracing for the Rest Of Your Life book.

clovers/src/objects/boxy.rs

@@ -129,4 +129,9 @@ impl<'scene> HitableTrait for Boxy<'scene> {
 
         sum
     }
+
+    // TODO: correctness for rotations/translations?
+    fn centroid(&self) -> Position {
+        self.aabb.centroid()
+    }
 }

clovers/src/objects/constant_medium.rs

@@ -145,4 +145,8 @@ impl<'scene> HitableTrait for ConstantMedium<'scene> {
         self.boundary
             .pdf_value(origin, direction, wavelength, time, rng)
     }
+
+    fn centroid(&self) -> Position {
+        self.boundary.centroid()
+    }
 }

clovers/src/objects/gltf.rs

@@ -110,6 +110,11 @@ impl<'scene> HitableTrait for GLTF<'scene> {
         self.bvhnode
             .pdf_value(origin, direction, wavelength, time, rng)
     }
+
+    // TODO: correctness?
+    fn centroid(&self) -> Position {
+        self.aabb.centroid()
+    }
 }
 
 fn parse_node<'scene>(
@@ -357,6 +362,11 @@ impl<'scene> HitableTrait for GLTFTriangle<'scene> {
             None => 0.0,
         }
     }
+
+    // TODO: correctness
+    fn centroid(&self) -> Position {
+        self.q + (self.u / 4.0) + (self.v / 4.0)
+    }
 }
 
 #[must_use]

clovers/src/objects/moving_sphere.rs

@@ -177,4 +177,9 @@ impl<'scene> HitableTrait for MovingSphere<'scene> {
         // TODO: fix
         0.0
     }
+
+    fn centroid(&self) -> Position {
+        // TODO: proper time support
+        self.center(0.5)
+    }
 }

clovers/src/objects/quad.rs

@@ -173,6 +173,11 @@ impl<'scene> HitableTrait for Quad<'scene> {
                 + (rng.gen::<Float>() * self.v);
         point - origin
     }
+
+    // TODO: correctness
+    fn centroid(&self) -> Position {
+        self.q + (self.u / 2.0) + (self.v / 2.0)
+    }
 }
 
 #[must_use]

clovers/src/objects/rotate.rs

@@ -176,4 +176,9 @@ impl<'scene> HitableTrait for RotateY<'scene> {
         // TODO: fix
         0.0
     }
+
+    // TODO: correctness!
+    fn centroid(&self) -> Position {
+        self.object.centroid()
+    }
 }

clovers/src/objects/sphere.rs

@@ -171,6 +171,10 @@ impl<'scene> HitableTrait for Sphere<'scene> {
         let vec = Unit::new_normalize(vec);
         *uvw.local(vec)
     }
+
+    fn centroid(&self) -> Position {
+        self.center
+    }
 }
 
 /// Internal helper.

clovers/src/objects/stl.rs

@@ -66,6 +66,11 @@ impl<'scene> HitableTrait for STL<'scene> {
     fn random(&self, origin: Position, rng: &mut SmallRng) -> Displacement {
         self.bvhnode.random(origin, rng)
     }
+
+    // TODO: correctness
+    fn centroid(&self) -> Position {
+        self.aabb.centroid()
+    }
 }
 
 /// STL structure. This gets converted into an internal representation using [Triangles](crate::objects::Triangle)

clovers/src/objects/translate.rs

@@ -95,4 +95,9 @@ impl<'scene> HitableTrait for Translate<'scene> {
         self.object
             .pdf_value(origin + self.offset, direction, wavelength, time, rng)
     }
+
+    // TODO: correctness
+    fn centroid(&self) -> Position {
+        self.object.centroid() + self.offset
+    }
 }

clovers/src/objects/triangle.rs

@@ -220,6 +220,11 @@ impl<'scene> HitableTrait for Triangle<'scene> {
 
         point - origin
     }
+
+    // TODO: correctness
+    fn centroid(&self) -> Position {
+        self.q + (self.u / 4.0) + (self.v / 4.0)
+    }
 }
 
 #[must_use]