WIP: pathtrace soup

To prepare for adding the handling of focal blur, move the film so that
it is behind the point of convergence of the lens.

In addition, store the distance to the focal plane in the camera, which
will be used when calculating rays with an non-zero aperture.

beevee/src/bvh/accelerated.rs

@@ -0,0 +1,39 @@
+use super::Intersected;
+use crate::aabb::Bounded;
+use crate::ray::Ray;
+
+/// The trait for any mesh-like object to be used in the [`BVH`]. If your object is not an
+/// aggregate, you should instead implement [`Intersected`] which derives this trait automatically.
+///
+/// This trait is there to accomodate for aggregate objects inside the [`BVH`]: you can implement a
+/// faster look-up of information using a [`BVH`] in a mesh for example, returning directly the
+/// reference to a hit triangle. This enables us to return this triangle instead of returning a
+/// reference to the whole mesh.
+///
+/// [`BVH`]: struct.BVH.html
+/// [`Intersected`]: struct.Intersected.html
+pub trait Accelerated: Bounded {
+    /// The type contained in your [`Accelerated`] structure
+    ///
+    /// [`Accelerated`]: struct.Accelerated.html
+    type Output;
+
+    /// Return None if no intersection happens with the ray, or a tuple of distance along the ray
+    /// and a reference to the object that was hit.
+    fn intersect(&self, ray: &Ray) -> Option<(f32, &Self::Output)>;
+}
+
+/// The automatic implementation for any [`Intersected`] object to be used in the [`BVH`].
+///
+/// [`BVH`]: struct.BVH.html
+impl<T> Accelerated for T
+where
+    T: Intersected,
+{
+    type Output = Self;
+
+    /// Return a reference to `self` when a distance was found.
+    fn intersect(&self, ray: &Ray) -> Option<(f32, &Self::Output)> {
+        self.intersect(ray).map(|t| (t, self))
+    }
+}

beevee/src/bvh/intersected.rs

@@ -1,8 +1,11 @@
 use crate::aabb::Bounded;
 use crate::ray::Ray;
 
-/// The trait for any object to be used in the [`BVH`].
+/// The trait for any object to be used in the [`BVH`]. Its derivation for [`Accelerated`] is
+/// automatically derived to return a reference to itself. If this not the intended semantics, see
+/// [`Accelerated`].
 ///
+/// [`Accelerated`]: struct.Accelerated.html
 /// [`BVH`]: struct.BVH.html
 pub trait Intersected: Bounded {
     /// Return None if there is no intersection, or the distance along the ray to the closest

beevee/src/bvh/mod.rs

@@ -1,5 +1,8 @@
 //! The Boudning Volume Hiearchy
 
+mod accelerated;
+pub use accelerated::*;
+
 mod intersected;
 pub use intersected::*;
 

beevee/src/bvh/tree.rs

@@ -1,4 +1,4 @@
-use super::Intersected;
+use super::Accelerated;
 use crate::aabb::AABB;
 use crate::ray::Ray;
 use crate::Axis;
@@ -23,9 +23,9 @@ struct Node {
 }
 
 /// The BVH containing all the objects of type O.
-/// This type must implement [`Intersected`].
+/// This type must implement [`Accelerated`].
 ///
-/// [`Intersected`]: trait.Intersected.html
+/// [`Accelerated`]: trait.Accelerated.html
 #[derive(Clone, Debug, PartialEq)]
 pub struct BVH {
     tree: Node,
@@ -92,7 +92,7 @@ impl BVH {
     /// let spheres: &mut [Sphere] = &mut [Sphere{ center: Point::origin(), radius: 2.5 }];
     /// let bvh = BVH::build(spheres);
     /// ```
-    pub fn build<O: Intersected>(objects: &mut [O]) -> Self {
+    pub fn build<O: Accelerated>(objects: &mut [O]) -> Self {
         Self::with_max_capacity(objects, 32)
     }
 
@@ -157,7 +157,7 @@ impl BVH {
     /// let spheres: &mut [Sphere] = &mut [Sphere{ center: Point::origin(), radius: 2.5 }];
     /// let bvh = BVH::with_max_capacity(spheres, 32);
     /// ```
-    pub fn with_max_capacity<O: Intersected>(objects: &mut [O], max_cap: usize) -> Self {
+    pub fn with_max_capacity<O: Accelerated>(objects: &mut [O], max_cap: usize) -> Self {
         let tree = build_node(objects, 0, objects.len(), max_cap);
         Self { tree }
     }
@@ -226,8 +226,8 @@ impl BVH {
     /// let bvh = BVH::with_max_capacity(spheres, 32);
     /// assert!(bvh.is_sound(spheres));
     /// ```
-    pub fn is_sound<O: Intersected>(&self, objects: &[O]) -> bool {
-        fn check_node<O: Intersected>(objects: &[O], node: &Node) -> bool {
+    pub fn is_sound<O: Accelerated>(&self, objects: &[O]) -> bool {
+        fn check_node<O: Accelerated>(objects: &[O], node: &Node) -> bool {
             if node.begin > node.end {
                 return false;
             }
@@ -322,17 +322,21 @@ impl BVH {
     /// assert_eq!(dist, 0.5);
     /// assert_eq!(obj, &spheres[0]);
     /// ```
-    pub fn walk<'o, O: Intersected>(&self, ray: &Ray, objects: &'o [O]) -> Option<(f32, &'o O)> {
+    pub fn walk<'o, O: Accelerated>(
+        &self,
+        ray: &Ray,
+        objects: &'o [O],
+    ) -> Option<(f32, &'o O::Output)> {
         walk_rec_helper(ray, objects, &self.tree, std::f32::INFINITY)
     }
 }
 
-fn walk_rec_helper<'o, O: Intersected>(
+fn walk_rec_helper<'o, O: Accelerated>(
     ray: &Ray,
     objects: &'o [O],
     node: &Node,
     min: f32,
-) -> Option<(f32, &'o O)> {
+) -> Option<(f32, &'o O::Output)> {
     use std::cmp::Ordering;
 
     match &node.kind {
@@ -340,7 +344,7 @@ fn walk_rec_helper<'o, O: Intersected>(
         NodeEnum::Leaf => objects[node.begin..node.end]
             .iter()
             // This turns the Option<f32> of an intersection into an Option<(f32, &O)>
-            .filter_map(|o| o.intersect(ray).map(|d| (d, o)))
+            .filter_map(|o| o.intersect(ray))
             // Discard values that are too far away
             .filter(|(dist, _)| dist < &min)
             // Only keep the minimum value, if there is one
@@ -382,14 +386,14 @@ fn walk_rec_helper<'o, O: Intersected>(
     }
 }
 
-fn bounds_from_slice<O: Intersected>(objects: &[O]) -> AABB {
+fn bounds_from_slice<O: Accelerated>(objects: &[O]) -> AABB {
     objects
         .iter()
         .map(|o| o.aabb())
         .fold(AABB::empty(), |acc, other| acc.union(&other))
 }
 
-fn build_node<O: Intersected>(objects: &mut [O], begin: usize, end: usize, max_cap: usize) -> Node {
+fn build_node<O: Accelerated>(objects: &mut [O], begin: usize, end: usize, max_cap: usize) -> Node {
     let aabb = bounds_from_slice(objects);
     // Don't split nodes under capacity
     if objects.len() <= max_cap {
@@ -401,7 +405,7 @@ fn build_node<O: Intersected>(objects: &mut [O], begin: usize, end: usize, max_c
         };
     }
     // Calculate the SAH heuristic for this slice
-    let (split, axis, cost) = compute_sah(&mut objects[begin..end], aabb.surface(), max_cap);
+    let (split, axis, cost) = compute_sah(objects, aabb.surface(), max_cap);
     // Only split if the heuristic shows that it is worth it
     if cost >= objects.len() as f32 {
         return Node {
@@ -411,11 +415,11 @@ fn build_node<O: Intersected>(objects: &mut [O], begin: usize, end: usize, max_c
             kind: NodeEnum::Leaf,
         };
     }
-    // Avoid degenerate cases, and recenter the split inside [begin, end)
-    let split = if split == 0 || split >= (end - begin - 1) {
-        begin + (end - begin) / 2
+    // Avoid degenerate cases
+    let split = if split <= 1 || split >= (objects.len() - 1) {
+        (end - begin) / 2
     } else {
-        begin + split
+        split
     };
     // Project along chosen axis
     pdqselect::select_by(objects, split, |lhs, rhs| {
@@ -424,8 +428,18 @@ fn build_node<O: Intersected>(objects: &mut [O], begin: usize, end: usize, max_c
             .expect("Can't use Nans in the SAH computation")
     });
     // Construct children recurivsely on [begin, split) and [split, end)
-    let left = Box::new(build_node(objects, begin, split, max_cap));
-    let right = Box::new(build_node(objects, split, end, max_cap));
+    let left = Box::new(build_node(
+        &mut objects[0..split],
+        begin,
+        begin + split,
+        max_cap,
+    ));
+    let right = Box::new(build_node(
+        &mut objects[split..],
+        begin + split,
+        end,
+        max_cap,
+    ));
     // Build the node recursivelly
     Node {
         bounds: aabb,
@@ -437,7 +451,7 @@ fn build_node<O: Intersected>(objects: &mut [O], begin: usize, end: usize, max_c
 
 /// Returns the index at which to split for SAH, the Axis along which to split, and the calculated
 /// cost.
-fn compute_sah<O: Intersected>(
+fn compute_sah<O: Accelerated>(
     objects: &mut [O],
     surface: f32,
     max_cap: usize,
@@ -481,7 +495,7 @@ fn compute_sah<O: Intersected>(
 
             let cost = 1. / max_cap as f32
                 + (left_count as f32 * left_surfaces[left_count - 1]
-                    + right_count as f32 * right_surfaces[right_count])
+                    + right_count as f32 * right_surfaces[right_count - 1])
                     / surface;
 
             if cost < min {

pathtracer/Cargo.toml

@@ -28,6 +28,7 @@ rand = "0.7"
 rayon = "1.3.0"
 serde_yaml = "0.8"
 structopt = "0.3"
+tobj = "1.0"
 
 [dependencies.nalgebra]
 version = "0.20.0"

pathtracer/examples/colorful.yaml

@@ -1,5 +1,5 @@
 # Optional field
-aliasing_limit: 10
+shot_rays: 10
 # Optional field
 reflection_limit: 5
 

pathtracer/examples/cornell-box.yaml

@@ -0,0 +1,24 @@
+reflection_limit: 5
+
+camera:
+  origin: [0.0, 1.0, 0.0]
+  forward: [ 0.0, 0.0, 1.0]
+  up: [0.0, 1.0, 0.0]
+  fov: 90.0
+  distance_to_image: 1.0
+  x: 2160
+  y: 2160
+
+lights:
+  ambients:
+    - color: {r: 0.1, g: 0.1, b: 0.1}
+  points:
+    - position: [-0.5, 1.0, 1.8]
+      color: {r: 1.0, g: 1.0, b: 1.0}
+
+meshes:
+  # FIXME: make the path relative to the YAML in some way?
+  # Easiest solution would be to chdir to the YAML's directory
+  - obj_file: "pathtracer/examples/objs/cornell-box.obj"
+    translation: [0.0, 0.0, 1.0]
+    rotation: [0, 180, 0]

pathtracer/examples/objs/cornell-box.mtl

@@ -0,0 +1,88 @@
+# The original Cornell Box in OBJ format.
+# Note that the real box is not a perfect cube, so
+# the faces are imperfect in this data set.
+#
+# Created by Guedis Cardenas and Morgan McGuire at Williams College, 2011
+# Released into the Public Domain.
+#
+# http://graphics.cs.williams.edu/data
+# http://www.graphics.cornell.edu/online/box/data.html
+#
+
+newmtl leftWall
+  Ns 10.0000
+  Ni 1.5000
+  illum 2
+  Ka 0.63 0.065 0.05 # Red
+  Kd 0.63 0.065 0.05
+  Ks 0 0 0
+  Ke 0 0 0
+
+
+newmtl rightWall
+  Ns 10.0000
+  Ni 1.5000
+  illum 2
+  Ka 0.14 0.45 0.091 # Green
+  Kd 0.14 0.45 0.091
+  Ks 0 0 0
+  Ke 0 0 0
+
+
+newmtl floor
+  Ns 10.0000
+  Ni 1.0000
+  illum 2
+  Ka 0.725 0.71 0.68 # White
+  Kd 0.725 0.71 0.68
+  Ks 0 0 0
+  Ke 0 0 0
+
+
+newmtl ceiling
+  Ns 10.0000
+  Ni 1.0000
+  illum 2
+  Ka 0.725 0.71 0.68 # White
+  Kd 0.725 0.71 0.68
+  Ks 0     0    0
+  Ke 0     0    0
+
+
+newmtl backWall
+  Ns 10.0000
+  Ni 1.0000
+  illum 2
+  Ka 0.725 0.71 0.68 # White
+  Kd 0.725 0.71 0.68
+  Ks 0 0 0
+  Ke 0 0 0
+
+
+newmtl shortBox
+  Ns 10.0000
+  Ni 1.0000
+  illum 2
+  Ka 0.725 0.71 0.68 # White
+  Kd 0.725 0.71 0.68
+  Ks 0 0 0
+  Ke 0 0 0
+
+
+newmtl tallBox
+  Ns 10.0000
+  Ni 1.0000
+  illum 2
+  Ka 0.725 0.71 0.68 # White
+  Kd 0.725 0.71 0.68
+  Ks 0 0 0
+  Ke 0 0 0
+
+newmtl light
+  Ns 10.0000
+  Ni 1.0000
+  illum 2
+  Ka 0.78 0.78 0.78 # White
+  Kd 0.78 0.78 0.78
+  Ks 0 0 0
+  Ke 17 12 4

pathtracer/examples/objs/cornell-box.obj

@@ -0,0 +1,168 @@
+# The original Cornell Box in OBJ format.
+# Note that the real box is not a perfect cube, so
+# the faces are imperfect in this data set.
+#
+# Created by Guedis Cardenas and Morgan McGuire at Williams College, 2011
+# Released into the Public Domain.
+#
+# http://graphics.cs.williams.edu/data
+# http://www.graphics.cornell.edu/online/box/data.html
+#
+
+mtllib cornell-box.mtl
+
+## Object floor
+v  -1.01  0.00   0.99
+v   1.00  0.00   0.99
+v   1.00  0.00  -1.04
+v  -0.99  0.00  -1.04
+
+g floor
+usemtl floor
+f -4 -3 -2 -1
+
+## Object ceiling
+v  -1.02  1.99   0.99
+v  -1.02  1.99  -1.04
+v   1.00  1.99  -1.04
+v   1.00  1.99   0.99
+
+g ceiling
+usemtl ceiling
+f -4 -3 -2 -1
+
+## Object backwall
+v  -0.99  0.00  -1.04
+v   1.00  0.00  -1.04
+v   1.00  1.99  -1.04
+v  -1.02  1.99  -1.04
+
+g backWall
+usemtl backWall
+f -4 -3 -2 -1
+
+## Object rightwall
+v	1.00  0.00  -1.04
+v	1.00  0.00   0.99
+v	1.00  1.99   0.99
+v	1.00  1.99  -1.04
+
+g rightWall
+usemtl rightWall
+f -4 -3 -2 -1
+
+## Object leftWall
+v  -1.01  0.00   0.99
+v  -0.99  0.00  -1.04
+v  -1.02  1.99  -1.04
+v  -1.02  1.99   0.99
+
+g leftWall
+usemtl leftWall
+f -4 -3 -2 -1
+
+## Object shortBox
+usemtl shortBox
+
+# Top Face
+v	0.53  0.60   0.75
+v	0.70  0.60   0.17
+v	0.13  0.60   0.00
+v  -0.05  0.60   0.57
+f -4 -3 -2 -1
+
+# Left Face
+v  -0.05  0.00   0.57
+v  -0.05  0.60   0.57
+v   0.13  0.60   0.00
+v   0.13  0.00   0.00
+f -4 -3 -2 -1
+
+# Front Face
+v	0.53  0.00   0.75
+v	0.53  0.60   0.75
+v  -0.05  0.60   0.57
+v  -0.05  0.00   0.57
+f -4 -3 -2 -1
+
+# Right Face
+v	0.70  0.00   0.17
+v	0.70  0.60   0.17
+v	0.53  0.60   0.75
+v	0.53  0.00   0.75
+f -4 -3 -2 -1
+
+# Back Face
+v	0.13  0.00   0.00
+v	0.13  0.60   0.00
+v	0.70  0.60   0.17
+v	0.70  0.00   0.17
+f -4 -3 -2 -1
+
+# Bottom Face
+v	0.53  0.00   0.75
+v	0.70  0.00   0.17
+v	0.13  0.00   0.00
+v  -0.05  0.00   0.57
+f -12 -11 -10 -9
+
+g shortBox
+usemtl shortBox
+
+## Object tallBox
+usemtl tallBox
+
+# Top Face
+v	-0.53  1.20   0.09
+v	 0.04  1.20  -0.09
+v	-0.14  1.20  -0.67
+v	-0.71  1.20  -0.49
+f -4 -3 -2 -1
+
+# Left Face
+v	-0.53  0.00   0.09
+v	-0.53  1.20   0.09
+v	-0.71  1.20  -0.49
+v	-0.71  0.00  -0.49
+f -4 -3 -2 -1
+
+# Back Face
+v	-0.71  0.00  -0.49
+v	-0.71  1.20  -0.49
+v	-0.14  1.20  -0.67
+v	-0.14  0.00  -0.67
+f -4 -3 -2 -1
+
+# Right Face
+v	-0.14  0.00  -0.67
+v	-0.14  1.20  -0.67
+v	 0.04  1.20  -0.09
+v	 0.04  0.00  -0.09
+f -4 -3 -2 -1
+
+# Front Face
+v	 0.04  0.00  -0.09
+v	 0.04  1.20  -0.09
+v	-0.53  1.20   0.09
+v	-0.53  0.00   0.09
+f -4 -3 -2 -1
+
+# Bottom Face
+v	-0.53  0.00   0.09
+v	 0.04  0.00  -0.09
+v	-0.14  0.00  -0.67
+v	-0.71  0.00  -0.49
+f -8 -7 -6 -5
+
+g tallBox
+usemtl tallBox
+
+## Object light
+v	-0.24  1.98   0.16
+v	-0.24  1.98  -0.22
+v	 0.23  1.98  -0.22
+v	 0.23  1.98   0.16
+
+g light
+usemtl light
+f -4 -3 -2 -1

pathtracer/examples/scene.yaml

@@ -1,4 +1,4 @@
-aliasing_limit: 10
+shot_rays: 10
 reflection_limit: 5
 background: {r: 0.5, g: 0.5, b: 0.5}
 

pathtracer/src/core/camera.rs

@@ -2,13 +2,18 @@
 
 use super::film::Film;
 use crate::{Point, Vector};
-use serde::{Deserialize, Deserializer};
+use beevee::ray::Ray;
+use nalgebra::Unit;
+use serde::Deserialize;
 
 /// Represent an abstract camera to observe the scene.
-#[derive(Debug, PartialEq)]
+#[serde(from = "SerializedCamera")]
+#[derive(Debug, PartialEq, Deserialize)]
 pub struct Camera {
-    /// Where the camera is set in the scene (i.e: its focal point).
+    /// Where the camera is set in the scene (i.e: the center of the lens).
     origin: Point,
+    /// How far away is the camera's focal plane.
+    distance_to_image: f32,
     /// The film to represent each pixel in the scene.
     film: Film,
 }
@@ -37,15 +42,20 @@ impl Camera {
         forward: Vector,
         up: Vector,
         fov: f32,
-        dist_to_image: f32,
+        distance_to_image: f32,
         x: u32,
         y: u32,
     ) -> Self {
         let right = forward.cross(&up);
-        let center = origin + forward.normalize() * dist_to_image;
-        let screen_size = 2. * f32::tan(fov / 2.) * dist_to_image;
-        let film = Film::new(x, y, screen_size, center, up, right);
-        Camera { origin, film }
+        let screen_size = 2. * f32::tan(fov / 2.);
+        // Construct the film behind the camera, upside down
+        let center = origin - forward.normalize();
+        let film = Film::new(x, y, screen_size, center, -up, -right);
+        Camera {
+            origin,
+            distance_to_image,
+            film,
+        }
     }
 
     /// Get the `Camera`'s [`Film`].
@@ -78,6 +88,24 @@ impl Camera {
     pub fn origin(&self) -> &Point {
         &self.origin
     }
+
+    /// Get the Ray coming out of the camera at a given ratio on the image.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use pathtracer::core::Camera;
+    /// # use pathtracer::Point;
+    /// #
+    /// let cam = Camera::default();
+    /// let ray_ul = cam.ray_with_ratio(0., 0.); // Ray coming out of the upper-left pixel
+    /// let ray_ul = cam.ray_with_ratio(1., 1.); // Ray coming out of the lower-right pixel
+    /// ```
+    pub fn ray_with_ratio(&self, x: f32, y: f32) -> Ray {
+        let pixel = self.film().pixel_at_ratio(x, y);
+        let direction = Unit::new_normalize(self.origin() - pixel);
+        Ray::new(pixel, direction)
+    }
 }
 
 impl Default for Camera {
@@ -140,16 +168,6 @@ impl From<SerializedCamera> for Camera {
     }
 }
 
-impl<'de> Deserialize<'de> for Camera {
-    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
-    where
-        D: Deserializer<'de>,
-    {
-        let cam: SerializedCamera = Deserialize::deserialize(deserializer)?;
-        Ok(cam.into())
-    }
-}
-
 #[cfg(test)]
 mod test {
     use super::*;
@@ -157,7 +175,7 @@ mod test {
     #[test]
     fn new_works() {
         let cam = Camera::new(
-            Point::new(-1., 0., 0.),
+            Point::new(1., 0., 0.),
             Vector::new(1., 0., 0.),
             Vector::new(0., 1., 0.),
             2. * f32::atan(1.), /* 90° in radian */
@@ -168,14 +186,15 @@ mod test {
         assert_eq!(
             cam,
             Camera {
-                origin: Point::new(-1., 0., 0.),
+                origin: Point::new(1., 0., 0.),
+                distance_to_image: 1.,
                 film: Film::new(
                     1080,
                     1080,
                     2.,
                     Point::origin(),
-                    Vector::new(0., 1., 0.),
-                    Vector::new(0., 0., 1.),
+                    -Vector::new(0., 1., 0.),
+                    -Vector::new(0., 0., 1.),
                 )
             }
         )
@@ -184,7 +203,7 @@ mod test {
     #[test]
     fn deserialization_works() {
         let yaml = r#"
-            origin: [-1.0, 0.0, 0.0]
+            origin: [1.0, 0.0, 0.0]
             forward: [ 1.0, 0.0, 0.0]
             up: [0.0, 1.0, 0.0]
             fov: 90.0
@@ -196,14 +215,15 @@ mod test {
         assert_eq!(
             cam,
             Camera {
-                origin: Point::new(-1., 0., 0.),
+                origin: Point::new(1., 0., 0.),
+                distance_to_image: 1.0,
                 film: Film::new(
                     1080,
                     1080,
                     2.,
                     Point::origin(),
-                    Vector::new(0., 1., 0.),
-                    Vector::new(0., 0., 1.),
+                    -Vector::new(0., 1., 0.),
+                    -Vector::new(0., 0., 1.),
                 )
             }
         )

pathtracer/src/core/color.rs

@@ -70,6 +70,25 @@ impl LinearColor {
         LinearColor { r, g, b }
     }
 
+    /// Creates a new `Color` from a slice.
+    ///
+    /// Panics if slice has less than 3 elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use pathtracer::core::LinearColor;
+    /// #
+    /// let color = LinearColor::from_slice(&[1.0, 0.0, 0.0]); // bright red!
+    /// ```
+    pub fn from_slice(s: &[f32]) -> Self {
+        LinearColor {
+            r: s[0],
+            g: s[1],
+            b: s[2],
+        }
+    }
+
     #[must_use]
     /// Clamps the color's RGB components between 0.0 and 1.0.
     ///

pathtracer/src/lib.rs

@@ -12,6 +12,7 @@ pub mod core;
 pub mod light;
 pub mod material;
 pub mod render;
+pub mod scene;
 pub mod serialize;
 pub mod shape;
 pub mod texture;

pathtracer/src/light/mod.rs

@@ -2,6 +2,7 @@
 
 use super::core::LinearColor;
 use super::{Point, Vector};
+use beevee::ray::Ray;
 use nalgebra::Unit;
 
 /// Represent a light in the scene being rendered.
@@ -16,6 +17,11 @@ pub trait SpatialLight: Light {
     fn to_source(&self, origin: &Point) -> (Unit<Vector>, f32);
 }
 
+/// Represent a light from which rays can be sampled
+pub trait SampleLight: SpatialLight {
+    fn sample_ray(&self) -> Ray;
+}
+
 mod ambient_light;
 pub use ambient_light::*;
 

pathtracer/src/light/point_light.rs

@@ -1,7 +1,9 @@
-use super::{Light, SpatialLight};
+use super::{Light, SampleLight, SpatialLight};
 use crate::core::LinearColor;
 use crate::{Point, Vector};
+use beevee::ray::Ray;
 use nalgebra::Unit;
+use rand::{distributions::Uniform, Rng};
 use serde::Deserialize;
 
 /// Represent a light emanating from a point in space, following the square distance law.
@@ -45,6 +47,37 @@ impl SpatialLight for PointLight {
         (Unit::new_normalize(delt), dist)
     }
 }
+impl SampleLight for PointLight {
+    /// Uniformly sample a ray from the point-light in a random direction.
+    ///
+    /// # Examles
+    ///
+    ///```
+    /// # use pathtracer::light::PointLight;
+    /// # use pathtracer::core::color::LinearColor;
+    /// # use pathtracer::Point;
+    /// #
+    /// let dir_light = PointLight::new(
+    ///     Point::origin(),
+    ///     LinearColor::new(1.0, 0.0, 1.0),
+    /// );
+    /// let sampled = dir_light.sample_ray();
+    /// ```
+    fn sample_ray(&self) -> Ray {
+        let mut rng = rand::thread_rng();
+        // Sample sphere uniformly
+        // See <https://mathworld.wolfram.com/SpherePointPicking.html>
+        let theta = rng.gen_range(0., std::f32::consts::PI * 2.);
+        let y = rng.sample(Uniform::new(-1., 1.)); // Inclusive for the poles
+        let dir = Unit::new_unchecked(Vector::new(
+            // this vector is already of unit length
+            f32::sqrt(1. - y * y) * f32::cos(theta),
+            y,
+            f32::sqrt(1. - y * y) * f32::sin(theta),
+        ));
+        Ray::new(self.position, dir)
+    }
+}
 
 #[cfg(test)]
 mod test {

pathtracer/src/light/spot_light.rs

@@ -1,13 +1,15 @@
-use super::{Light, SpatialLight};
+use super::{Light, SampleLight, SpatialLight};
 use crate::core::LinearColor;
 use crate::{Point, Vector};
+use beevee::ray::Ray;
+use nalgebra::Rotation3;
 use nalgebra::Unit;
-use serde::{Deserialize, Deserializer};
+use rand::{distributions::Uniform, Rng};
+use serde::Deserialize;
 
 /// 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)]
+#[serde(from = "SerializedSpotLight")]
+#[derive(Debug, PartialEq, Deserialize)]
 pub struct SpotLight {
     position: Point,
     direction: Unit<Vector>,
@@ -66,6 +68,52 @@ impl SpatialLight for SpotLight {
         (Unit::new_normalize(delt), dist)
     }
 }
+impl SampleLight for SpotLight {
+    /// Uniformly sample a ray from the spot-light in a random direction.
+    ///
+    /// # Examles
+    ///
+    ///```
+    /// # use pathtracer::light::SpotLight;
+    /// # use pathtracer::core::color::LinearColor;
+    /// # use pathtracer::{Point, Vector};
+    /// #
+    /// let spot_light = SpotLight::degrees_new(
+    ///     Point::origin(),
+    ///     Vector::x_axis(),
+    ///     90.,
+    ///     LinearColor::new(1.0, 0.0, 1.0),
+    /// );
+    /// let sampled = spot_light.sample_ray();
+    /// ```
+    fn sample_ray(&self) -> Ray {
+        let mut rng = rand::thread_rng();
+        // Sample cap at Z-pole uniformly
+        // See <https://math.stackexchange.com/questions/56784>
+        let theta = rng.gen_range(0., std::f32::consts::PI * 2.);
+        let z = rng.sample(Uniform::new(self.cosine_value, 1.)); // Inclusive for the poles
+        let dir = Unit::new_unchecked(Vector::new(
+            // this vector is already of unit length
+            f32::sqrt(1. - z * z) * f32::cos(theta),
+            f32::sqrt(1. - z * z) * f32::sin(theta),
+            z,
+        ));
+        let dir =
+            if let Some(rotate) = Rotation3::rotation_between(&Vector::z_axis(), &self.direction) {
+                // Rotate the direction if needed
+                rotate * dir
+            } else if self.direction.dot(&dir) < 0. {
+                // Special case if the direction is directly opposite, its rotation axis is
+                // undefined, but we don't care about a special axis to perform the rotation
+                -dir
+            } else {
+                dir
+            };
+        // We should now be oriented the right way
+        debug_assert!(self.direction.dot(&dir) >= self.cosine_value);
+        Ray::new(self.position, dir)
+    }
+}
 
 #[derive(Debug, Deserialize)]
 struct SerializedSpotLight {
@@ -82,16 +130,6 @@ impl From<SerializedSpotLight> for SpotLight {
     }
 }
 
-impl<'de> Deserialize<'de> for SpotLight {
-    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
-    where
-        D: Deserializer<'de>,
-    {
-        let cam: SerializedSpotLight = Deserialize::deserialize(deserializer)?;
-        Ok(cam.into())
-    }
-}
-
 #[cfg(test)]
 mod test {
     use super::*;

pathtracer/src/main.rs

@@ -1,7 +1,18 @@
-use pathtracer::render::Scene;
+use pathtracer::render::{Pathtracer, Raytracer};
+use pathtracer::scene::Scene;
 use std::path::PathBuf;
+use std::str;
+use structopt::clap::arg_enum;
 use structopt::StructOpt;
 
+arg_enum! {
+    #[derive(Debug)]
+    enum RenderOption {
+        Raytracer,
+        Pathtracer,
+    }
+}
+
 #[derive(StructOpt, Debug)]
 struct Options {
     /// Input description for the scene to be rendered.
@@ -10,6 +21,15 @@ struct Options {
     /// Output image for the rendered scene.
     #[structopt(short, long, parse(from_os_str), default_value = "scene.png")]
     output: PathBuf,
+    /// Which renderer should be used on the input scene.
+    #[structopt(
+        short,
+        long,
+        possible_values = &RenderOption::variants(),
+        case_insensitive = true,
+        default_value = "Raytracer"
+    )]
+    renderer: RenderOption,
 }
 
 fn main() -> Result<(), Box<dyn std::error::Error>> {
@@ -17,7 +37,10 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     let f = std::fs::File::open(options.input)?;
 
     let scene: Scene = serde_yaml::from_reader(f)?;
-    let image = scene.render();
+    let image = match options.renderer {
+        RenderOption::Raytracer => Raytracer::new(scene).render(),
+        RenderOption::Pathtracer => Pathtracer::new(scene).render(),
+    };
 
     image.save(options.output)?;
     Ok(())

pathtracer/src/material/mod.rs

@@ -9,10 +9,11 @@ use serde::Deserialize;
 #[serde(rename_all = "lowercase")]
 #[allow(missing_docs)]
 #[enum_dispatch::enum_dispatch]
-#[derive(Debug, PartialEq, Deserialize)]
+#[derive(Debug, Clone, PartialEq, Deserialize)]
 pub enum MaterialEnum {
     #[serde(rename = "uniform")]
     UniformMaterial,
+    TriangleMaterial,
 }
 
 /// Represent the physical light properties of an object in the scene;
@@ -22,5 +23,8 @@ pub trait Material: std::fmt::Debug {
     fn properties(&self, point: Point2D) -> LightProperties;
 }
 
+mod triangle;
+pub use triangle::*;
+
 mod uniform;
 pub use uniform::*;

pathtracer/src/material/triangle.rs

@@ -0,0 +1,31 @@
+use super::Material;
+use crate::core::{LightProperties, LinearColor, ReflTransEnum};
+use crate::Point2D;
+use serde::Deserialize;
+
+/// Represent a material which interpolates between three points.
+#[derive(Debug, Clone, PartialEq, Deserialize)]
+pub struct TriangleMaterial {
+    /// The diffuse components.
+    diffuse: [LinearColor; 3],
+    /// The specular components.
+    specular: [LinearColor; 3],
+    /// The transparency or reflectivity properties, this is not interpolated.
+    #[serde(flatten)]
+    pub refl_trans: Option<ReflTransEnum>,
+}
+
+impl Material for TriangleMaterial {
+    fn properties(&self, point: Point2D) -> LightProperties {
+        let (u, v) = (point.x, point.y);
+        let diffuse = self.diffuse[0].clone() * (1. - u - v)
+            + self.diffuse[1].clone() * u
+            + self.diffuse[2].clone() * v;
+        let specular = self.specular[0].clone() * (1. - u - v)
+            + self.specular[1].clone() * u
+            + self.specular[2].clone() * v;
+        LightProperties::new(diffuse, specular, self.refl_trans.clone())
+    }
+}
+
+// FIXME: tests

pathtracer/src/render/mod.rs

@@ -1,12 +1,18 @@
-//! Rendering logic
+//! Define the different kinds of renderers for use on a given scene.
+use image::RgbImage;
 
-pub mod light_aggregate;
-pub use light_aggregate::*;
+/// Each renderer implements this trait, to be called after being built.
+pub trait Renderer {
+    /// Render the [`Scene`] using the chosen rendering technique.
+    ///
+    /// [`Scene`]: ../scene/scene/struct.Scene.html
+    fn render(&self) -> RgbImage;
+}
 
-pub mod object;
-pub use object::*;
+mod pathtrace;
+pub use pathtrace::*;
 
-pub mod scene;
-pub use scene::*;
+mod raytracer;
+pub use raytracer::*;
 
 pub(crate) mod utils;

pathtracer/src/render/pathtrace/light_path.rs

@@ -0,0 +1,37 @@
+use crate::core::{LightProperties, LinearColor};
+use crate::light::SampleLight;
+use crate::Point;
+
+pub struct LightPathPoint {
+    pub point: Point,
+    pub luminance: LinearColor,
+    pub properties: LightProperties,
+}
+
+impl LightPathPoint {
+    pub fn new(point: Point, luminance: LinearColor, properties: LightProperties) -> Self {
+        LightPathPoint {
+            point,
+            luminance,
+            properties,
+        }
+    }
+}
+
+pub struct LightPath<'a> {
+    pub origin: &'a dyn SampleLight,
+    pub points: Vec<LightPathPoint>,
+}
+
+impl<'a> LightPath<'a> {
+    pub fn new(origin: &'a dyn SampleLight) -> Self {
+        LightPath {
+            origin,
+            points: Vec::new(),
+        }
+    }
+
+    pub fn push_point(&mut self, new_point: LightPathPoint) {
+        self.points.push(new_point)
+    }
+}

pathtracer/src/render/pathtrace/mod.rs

@@ -0,0 +1,4 @@
+mod light_path;
+
+mod pathtracer;
+pub use self::pathtracer::*;

pathtracer/src/render/pathtrace/pathtracer.rs

@@ -0,0 +1,97 @@
+use super::super::utils::*;
+use super::super::Renderer;
+use super::light_path::{LightPath, LightPathPoint};
+use crate::core::{LightProperties, LinearColor};
+use crate::light::SampleLight;
+use crate::material::Material;
+use crate::scene::object::Object;
+use crate::scene::Scene;
+use crate::shape::Shape;
+use crate::{Point, Vector};
+use beevee::ray::Ray;
+use image::RgbImage;
+use nalgebra::Unit;
+use rand::Rng;
+
+/// Render the [`Scene`] using Bidirectional-Pathtracing
+///
+/// [`Scene`]: ../scene/scene/struct.Scene.html
+pub struct Pathtracer {
+    #[allow(unused)]
+    scene: Scene,
+}
+
+impl Pathtracer {
+    /// Create a [`Pathtracer`] renderer with the given [`Scene`]
+    ///
+    /// [`Pathtracer`]: struct.Pathtracer.html
+    /// [`Scene`]: ../scene/scene/struct.Scene.html
+    pub fn new(scene: Scene) -> Self {
+        Pathtracer { scene }
+    }
+
+    /// Render the [`Scene`] using Bidirectional-Pathtracing.
+    ///
+    /// [`Scene`]: ../scene/scene/struct.Scene.html
+    pub fn render(&self) -> RgbImage {
+        todo!()
+    }
+
+    fn cast_ray(&self, ray: Ray) -> Option<(f32, &Object)> {
+        self.scene.bvh.walk(&ray, &self.scene.objects)
+    }
+
+    fn construct_light_path(&self) -> LightPath {
+        let mut rng = rand::thread_rng();
+        let num_lights = self.scene.lights.points.len() + self.scene.lights.spots.len();
+        let index = rng.gen_range(0, num_lights);
+
+        let sample_light: &dyn SampleLight = if index < self.scene.lights.points.len() {
+            &self.scene.lights.points[index]
+        } else {
+            &self.scene.lights.spots[index - self.scene.lights.points.len()]
+        };
+
+        let mut ray = sample_light.sample_ray();
+        let mut res = LightPath::new(sample_light);
+
+        if let Some((dist, obj)) = self.cast_ray(ray) {
+            let hit_pos = ray.origin + ray.direction.as_ref() * dist;
+            let texel = obj.shape.project_texel(&hit_pos);
+            let new_point = LightPathPoint::new(
+                hit_pos,
+                sample_light.illumination(&hit_pos),
+                obj.material.properties(texel),
+            );
+            res.push_point(new_point);
+            ray = todo!(); // Sample new direction
+        } else {
+            return res;
+        };
+
+        for _ in 1..self.scene.reflection_limit {
+            if let Some((dist, obj)) = self.cast_ray(ray) {
+                let new_point = todo!();
+                res.push_point(new_point);
+            } else {
+                break;
+            }
+        }
+        res
+    }
+
+    fn illuminate(
+        &self,
+        point: Point,
+        properties: LightProperties,
+        path: LightPath,
+    ) -> LinearColor {
+        path.points.iter().map(|p| p.luminance.clone()).sum()
+    }
+}
+
+impl Renderer for Pathtracer {
+    fn render(&self) -> RgbImage {
+        self.render()
+    }
+}

pathtracer/src/render/raytracer.rs

@@ -1,93 +1,43 @@
-//! Scene rendering logic
-
-use super::{light_aggregate::LightAggregate, object::Object, utils::*};
+use super::utils::*;
+use super::Renderer;
+use crate::scene::{Object, Scene};
 use crate::{
-    core::{Camera, LightProperties, LinearColor, ReflTransEnum},
+    core::{LightProperties, LinearColor, ReflTransEnum},
     material::Material,
     shape::Shape,
     texture::Texture,
     {Point, Vector},
 };
-use beevee::{bvh::BVH, ray::Ray};
+use beevee::ray::Ray;
 use image::RgbImage;
 use nalgebra::Unit;
 use rand::prelude::thread_rng;
 use rand::Rng;
-use serde::{Deserialize, Deserializer};
 
-/// Represent the scene being rendered.
-pub struct Scene {
-    camera: Camera,
-    lights: LightAggregate,
-    objects: Vec<Object>,
-    bvh: BVH,
-    background: LinearColor,
-    aliasing_limit: u32,
-    reflection_limit: u32,
-    diffraction_index: f32,
+/// Render the [`Scene`] using Raytracing.
+///
+/// [`Scene`]: ../scene/scene/struct.Scene.html
+pub struct Raytracer {
+    scene: Scene,
 }
 
-impl Scene {
-    /// Creates a new `Scene`.
+impl Raytracer {
+    /// Create a [`Raytracer`] renderer with the given [`Scene`]
     ///
-    /// # Examples
-    ///
-    /// ```
-    /// # use pathtracer::core::{Camera, LightProperties, LinearColor};
-    /// # use pathtracer::material::UniformMaterial;
-    /// # use pathtracer::render::{LightAggregate, Object, Scene};
-    /// # use pathtracer::shape::Sphere;
-    /// # use pathtracer::texture::UniformTexture;
-    /// # use pathtracer::Point;
-    /// #
-    /// let scene = Scene::new(
-    ///     Camera::default(),
-    ///     LightAggregate::empty(),
-    ///     vec![
-    ///         Object::new(
-    ///             Sphere::new(Point::origin(), 1.0).into(),
-    ///             UniformMaterial::new(
-    ///                 LightProperties::new(
-    ///                     LinearColor::new(1.0, 0.0, 0.0), // diffuse component
-    ///                     LinearColor::new(0.0, 0.0, 0.0), // specular component
-    ///                     None,
-    ///                 ),
-    ///             ).into(),
-    ///             UniformTexture::new(LinearColor::new(0.5, 0.5, 0.5)).into(),
-    ///         ),
-    ///     ],
-    ///     LinearColor::black(), // Background color
-    ///     5,   // aliasing limit
-    ///     3,   // reflection recursion limit
-    ///     0.0, // diffraction index
-    /// );
-    /// ```
-    pub fn new(
-        camera: Camera,
-        lights: LightAggregate,
-        mut objects: Vec<Object>,
-        background: LinearColor,
-        aliasing_limit: u32,
-        reflection_limit: u32,
-        diffraction_index: f32,
-    ) -> Self {
-        // NOTE(Antoine): fun fact: BVH::build stack overflows when given an empty slice :)
-        let bvh = BVH::build(&mut objects);
-        Scene {
-            camera,
-            lights,
-            objects,
-            bvh,
-            background,
-            aliasing_limit,
-            reflection_limit,
-            diffraction_index,
-        }
+    /// [`Raytracer`]: struct.Raytracer.html
+    /// [`Scene`]: ../scene/scene/struct.Scene.html
+    pub fn new(scene: Scene) -> Self {
+        Raytracer { scene }
     }
 
-    /// Render the scene into an image.
+    /// Render the [`Scene`] using Raytracing.
+    ///
+    /// [`Scene`]: ../scene/scene/struct.Scene.html
     pub fn render(&self) -> RgbImage {
-        let mut image = RgbImage::new(self.camera.film().width(), self.camera.film().height());
+        let mut image = RgbImage::new(
+            self.scene.camera.film().width(),
+            self.scene.camera.film().height(),
+        );
 
         let total = (image.width() * image.height()) as u64;
         let pb = indicatif::ProgressBar::new(total);
@@ -96,7 +46,7 @@ impl Scene {
             "{spinner:.green} [{elapsed_precise}] [{wide_bar:.cyan/blue}] {percent:>3}%: {pos}/{len} pixels (ETA: {eta})",
         ));
 
-        let pixel_func = if self.aliasing_limit > 0 {
+        let pixel_func = if self.scene.shot_rays > 0 {
             Self::anti_alias_pixel
         } else {
             Self::pixel
@@ -121,18 +71,17 @@ impl Scene {
 
     /// Get pixel color for (x, y) a pixel **coordinate**
     fn pixel(&self, x: f32, y: f32) -> LinearColor {
-        let (x, y) = self.camera.film().pixel_ratio(x, y);
-        let pixel = self.camera.film().pixel_at_ratio(x, y);
-        let direction = Unit::new_normalize(pixel - self.camera.origin());
-        let indices = RefractionInfo::with_index(self.diffraction_index);
-        self.cast_ray(Ray::new(pixel, direction)).map_or_else(
-            || self.background.clone(),
+        let (x, y) = self.scene.camera.film().pixel_ratio(x, y);
+        let indices = RefractionInfo::with_index(self.scene.diffraction_index);
+        let ray = self.scene.camera.ray_with_ratio(x, y);
+        self.cast_ray(ray).map_or_else(
+            || self.scene.background.clone(),
             |(t, obj)| {
                 self.color_at(
-                    pixel + direction.as_ref() * t,
+                    ray.origin + ray.direction.as_ref() * t,
                     obj,
-                    direction,
-                    self.reflection_limit,
+                    ray.direction,
+                    self.scene.reflection_limit,
                     indices,
                 )
             },
@@ -141,7 +90,7 @@ impl Scene {
 
     /// Get pixel color with anti-aliasing
     fn anti_alias_pixel(&self, x: f32, y: f32) -> LinearColor {
-        let range = 0..self.aliasing_limit;
+        let range = 0..self.scene.shot_rays;
         let mut rng = thread_rng();
         let acc: LinearColor = range
             .map(|_| {
@@ -151,11 +100,11 @@ impl Scene {
             })
             .map(LinearColor::clamp)
             .sum();
-        acc / self.aliasing_limit as f32
+        acc / self.scene.shot_rays as f32
     }
 
     fn cast_ray(&self, ray: Ray) -> Option<(f32, &Object)> {
-        self.bvh.walk(&ray, &self.objects)
+        self.scene.bvh.walk(&ray, &self.scene.objects)
     }
 
     fn color_at(
@@ -173,6 +122,9 @@ impl Scene {
         let normal = object.shape.normal(&point);
         let reflected_ray = reflected(incident_ray, normal);
 
+        // FIXME: change this to averaged sampled rays instead of visiting every light ?
+        // Indeed the path-tracing algorithm is good for calculating the radiance at a point
+        // But it should be used for reflection and refraction too...
         let lighting = self.illuminate(point, object_color, &properties, normal, reflected_ray);
         if properties.refl_trans.is_none() {
             // Avoid calculating reflection when not needed
@@ -261,7 +213,8 @@ impl Scene {
     }
 
     fn illuminate_ambient(&self, color: LinearColor) -> LinearColor {
-        self.lights
+        self.scene
+            .lights
             .ambient_lights_iter()
             .map(|light| color.clone() * light.illumination(&Point::origin()))
             .map(LinearColor::clamp)
@@ -275,11 +228,12 @@ impl Scene {
         normal: Unit<Vector>,
         reflected: Unit<Vector>,
     ) -> LinearColor {
-        self.lights
+        self.scene
+            .lights
             .spatial_lights_iter()
             .map(|light| {
                 let (direction, t) = light.to_source(&point);
-                let light_ray = Ray::new(point + 0.001 * direction.as_ref(), direction);
+                let light_ray = Ray::new(point + direction.as_ref() * 0.001, direction);
                 match self.cast_ray(light_ray) {
                     // Take shadows into account
                     Some((obstacle_t, _)) if obstacle_t < t => return LinearColor::black(),
@@ -295,72 +249,8 @@ impl Scene {
     }
 }
 
-#[derive(Debug, PartialEq, Deserialize)]
-struct SerializedScene {
-    camera: Camera,
-    #[serde(default)]
-    lights: LightAggregate,
-    #[serde(default)]
-    objects: Vec<Object>,
-    #[serde(default)]
-    background: LinearColor,
-    #[serde(default)]
-    aliasing_limit: u32,
-    #[serde(default)]
-    reflection_limit: u32,
-    #[serde(default = "crate::serialize::default_identity")]
-    starting_diffraction: f32,
-}
-
-impl From<SerializedScene> for Scene {
-    fn from(scene: SerializedScene) -> Self {
-        Scene::new(
-            scene.camera,
-            scene.lights,
-            scene.objects,
-            scene.background,
-            scene.aliasing_limit,
-            scene.reflection_limit,
-            scene.starting_diffraction,
-        )
-    }
-}
-
-impl<'de> Deserialize<'de> for Scene {
-    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
-    where
-        D: Deserializer<'de>,
-    {
-        let cam: SerializedScene = Deserialize::deserialize(deserializer)?;
-        Ok(cam.into())
-    }
-}
-
-#[cfg(test)]
-mod test {
-    use super::*;
-
-    #[test]
-    fn deserialization_works() {
-        let yaml = std::include_str!("../../examples/scene.yaml");
-        let _: Scene = serde_yaml::from_str(yaml).unwrap();
-        // FIXME: actually test the equality ?
-    }
-
-    #[test]
-    #[ignore] // stack overflow because of BVH :(
-    fn bvh_fails() {
-        use crate::core::Camera;
-        use crate::render::{LightAggregate, Scene};
-
-        let _scene = Scene::new(
-            Camera::default(),
-            LightAggregate::empty(),
-            Vec::new(),           // Objects list
-            LinearColor::black(), // Background color
-            5,                    // aliasing limit
-            3,                    // reflection recursion limit
-            0.0,                  // diffraction index
-        );
+impl Renderer for Raytracer {
+    fn render(&self) -> RgbImage {
+        self.render()
     }
 }

pathtracer/src/render/utils.rs

@@ -1,5 +1,7 @@
 use crate::Vector;
 use nalgebra::Unit;
+use rand::prelude::thread_rng;
+use rand::Rng;
 
 pub fn reflected(incident: Unit<Vector>, normal: Unit<Vector>) -> Unit<Vector> {
     let proj = incident.dot(&normal);
@@ -65,3 +67,58 @@ impl RefractionInfo {
         std::mem::swap(&mut self.old_index, &mut self.new_index)
     }
 }
+
+/// Returns a random ray in the hemisphere described by a normal unit-vector, and the probability
+/// to have picked that direction.
+#[allow(unused)] // FIXME: remove once used
+pub fn sample_hemisphere(normal: Vector) -> (Vector, f32) {
+    let mut rng = thread_rng();
+    let azimuth = rng.gen::<f32>() * std::f32::consts::PI * 2.;
+    // Cosine weighted importance sampling
+    let cos_elevation: f32 = rng.gen();
+    let sin_elevation = f32::sqrt(1. - cos_elevation * cos_elevation);
+
+    let x = sin_elevation * azimuth.cos();
+    let y = cos_elevation;
+    let z = sin_elevation * azimuth.sin();
+
+    // Calculate orthonormal base, defined by (normalb_b, normal, normal_t)
+    // Pay attention to degenerate cases when (y, z) is small for use with cross product
+    let normal_t = if normal.x.abs() > normal.y.abs() {
+        Vector::new(normal.z, 0., -normal.x).normalize()
+    } else {
+        Vector::new(0., -normal.z, normal.y).normalize()
+    };
+    let normal_b = normal.cross(&normal_t);
+
+    // Perform the matrix calculation by hand...
+    let scattered = Vector::new(
+        x * normal_b.x + y * normal.x + z * normal_t.x,
+        x * normal_b.y + y * normal.y + z * normal_t.y,
+        x * normal_b.z + y * normal.z + z * normal_t.z,
+    );
+
+    // The probability to have picked the ray is inversely proportional to cosine of the angle with
+    // the normal
+    (scattered, 1. / scattered.dot(&normal))
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn sample_hemisphere_work() {
+        // NOTE(Bruno): should use some test-case generation for failure-reproduction purposes...
+        let mut rng = thread_rng();
+        for _ in 0..100 {
+            let normal = Vector::new(rng.gen(), rng.gen(), rng.gen());
+            for _ in 0..100 {
+                let (sample, proportion) = sample_hemisphere(normal);
+                let cos_angle = normal.dot(&sample);
+                assert!(cos_angle >= 0.);
+                assert!(1. / cos_angle - proportion < std::f32::EPSILON);
+            }
+        }
+    }
+}

pathtracer/src/scene/light_aggregate.rs

@@ -8,13 +8,13 @@ use std::iter::Iterator;
 /// A struct centralizing the light computation logic.
 pub struct LightAggregate {
     #[serde(default)]
-    ambients: Vec<AmbientLight>,
+    pub(crate) ambients: Vec<AmbientLight>,
     #[serde(default)]
-    directionals: Vec<DirectionalLight>,
+    pub(crate) directionals: Vec<DirectionalLight>,
     #[serde(default)]
-    points: Vec<PointLight>,
+    pub(crate) points: Vec<PointLight>,
     #[serde(default)]
-    spots: Vec<SpotLight>,
+    pub(crate) spots: Vec<SpotLight>,
 }
 
 impl LightAggregate {
@@ -23,7 +23,7 @@ impl LightAggregate {
     /// # Examples
     ///
     /// ```
-    /// # use pathtracer::render::LightAggregate;
+    /// # use pathtracer::scene::LightAggregate;
     /// #
     /// let la = LightAggregate::empty();
     /// assert_eq!(la.ambient_lights_iter().count(), 0);
@@ -40,7 +40,7 @@ impl LightAggregate {
     /// # Examples
     ///
     /// ```
-    /// # use pathtracer::render::LightAggregate;
+    /// # use pathtracer::scene::LightAggregate;
     /// #
     /// let la = LightAggregate::new(
     ///     Vec::new(),

pathtracer/src/scene/mesh.rs

@@ -0,0 +1,133 @@
+use std::convert::TryFrom;
+use std::path::PathBuf;
+
+use nalgebra::{Similarity3, Unit, VectorSlice3};
+
+use serde::Deserialize;
+
+use tobj::{self, load_obj};
+
+use super::Object;
+use crate::{
+    core::{LightProperties, LinearColor},
+    material::{MaterialEnum, UniformMaterial},
+    shape::{InterpolatedTriangle, ShapeEnum, Triangle},
+    texture::{TextureEnum, UniformTexture},
+    Point, Vector,
+};
+
+/// Represent a mesh of objects.
+#[serde(try_from = "Wavefront")]
+#[derive(Debug, PartialEq, Deserialize)]
+pub struct Mesh {
+    /// The shapes composing the mesh
+    pub(crate) shapes: Vec<Object>,
+}
+
+#[derive(Debug, PartialEq, Deserialize)]
+pub(crate) struct Wavefront {
+    pub obj_file: PathBuf,
+    #[serde(default = "nalgebra::zero")]
+    translation: Vector,
+    #[serde(default = "nalgebra::zero")]
+    rotation: Vector,
+    #[serde(default = "crate::serialize::coefficient::default_identity")]
+    scale: f32,
+}
+
+impl TryFrom<Wavefront> for Mesh {
+    type Error = tobj::LoadError;
+
+    fn try_from(wavefront: Wavefront) -> Result<Mesh, Self::Error> {
+        let mut shapes = Vec::new();
+
+        let (models, materials) = load_obj(&wavefront.obj_file)?;
+
+        // The object to world transformation matrix
+        let transform = Similarity3::new(
+            wavefront.translation,
+            wavefront.rotation * std::f32::consts::PI / 180., // From degrees to radians
+            wavefront.scale,
+        );
+
+        for model in models {
+            let mesh = &model.mesh;
+
+            // mesh.indices contains all vertices. Each group of 3 vertices
+            // is a triangle, so we iterate over indices 3 by 3.
+            for i in 0..(mesh.indices.len() / 3) {
+                let (a, b, c) = (
+                    mesh.indices[i * 3] as usize,
+                    mesh.indices[i * 3 + 1] as usize,
+                    mesh.indices[i * 3 + 2] as usize,
+                );
+
+                let pos_a = transform * Point::from_slice(&mesh.positions[(a * 3)..(a * 3 + 3)]);
+                let pos_b = transform * Point::from_slice(&mesh.positions[(b * 3)..(b * 3 + 3)]);
+                let pos_c = transform * Point::from_slice(&mesh.positions[(c * 3)..(c * 3 + 3)]);
+
+                let triangle: ShapeEnum = if mesh.normals.is_empty() {
+                    Triangle::new(pos_a, pos_b, pos_c).into()
+                } else {
+                    // We apply the (arguably useless) scaling to the vectors in case it is
+                    // negative, which would invert their direction
+                    let norm_a = {
+                        let vec: Vector =
+                            VectorSlice3::from_slice(&mesh.normals[(a * 3)..(a * 3 + 3)]).into();
+                        Unit::new_normalize(transform * vec)
+                    };
+                    let norm_b = {
+                        let vec: Vector =
+                            VectorSlice3::from_slice(&mesh.normals[(b * 3)..(b * 3 + 3)]).into();
+                        Unit::new_normalize(transform * vec)
+                    };
+                    let norm_c = {
+                        let vec: Vector =
+                            VectorSlice3::from_slice(&mesh.normals[(c * 3)..(c * 3 + 3)]).into();
+                        Unit::new_normalize(transform * vec)
+                    };
+
+                    InterpolatedTriangle::new(pos_a, pos_b, pos_c, norm_a, norm_b, norm_c).into()
+                };
+
+                // FIXME: handle material
+                let (material, texture): (MaterialEnum, TextureEnum) =
+                    if let Some(mat_id) = mesh.material_id {
+                        let mesh_mat = &materials[mat_id];
+
+                        let diffuse = LinearColor::from_slice(&mesh_mat.ambient[..]);
+                        let specular = LinearColor::from_slice(&mesh_mat.ambient[..]);
+
+                        let material = UniformMaterial::new(LightProperties::new(
+                            diffuse.clone(),
+                            specular,
+                            // FIXME: material.dissolve is supposed to be "the alpha term"
+                            // Needs translation to our ReflTransEnum
+                            None,
+                        ));
+
+                        // we only handle uniform textures
+                        let texture = UniformTexture::new(diffuse);
+
+                        (material.into(), texture.into())
+                    } else {
+                        // FIXME: should we accept this, and use a default
+                        // Material, or throw a LoadError
+                        (
+                            UniformMaterial::new(LightProperties::new(
+                                LinearColor::new(0.5, 0.5, 0.5),
+                                LinearColor::new(0.1, 0.1, 0.1),
+                                None,
+                            ))
+                            .into(),
+                            UniformTexture::new(LinearColor::new(0.5, 0.5, 0.5)).into(),
+                        )
+                    };
+
+                shapes.push(Object::new(triangle, material, texture));
+            }
+        }
+
+        Ok(Mesh { shapes })
+    }
+}

pathtracer/src/scene/mod.rs

@@ -0,0 +1,13 @@
+//! Desciption of the scene.
+
+pub mod light_aggregate;
+pub use light_aggregate::*;
+
+mod mesh;
+pub use mesh::*;
+
+pub mod object;
+pub use object::*;
+
+pub mod scene;
+pub use scene::*;

pathtracer/src/scene/object.rs

@@ -1,7 +1,7 @@
 //! Logic for the scene objects
 
 use crate::material::MaterialEnum;
-use crate::shape::{Shape, ShapeEnum};
+use crate::shape::ShapeEnum;
 use crate::texture::TextureEnum;
 use crate::Point;
 use beevee::{
@@ -12,7 +12,7 @@ use beevee::{
 use serde::Deserialize;
 
 /// An object being rendered in the scene.
-#[derive(Debug, PartialEq, Deserialize)]
+#[derive(Debug, Clone, PartialEq, Deserialize)]
 pub struct Object {
     /// The `Object`'s physical shape
     pub shape: ShapeEnum,
@@ -30,7 +30,7 @@ impl Object {
     /// ```
     /// # use pathtracer::core::{LightProperties, LinearColor};
     /// # use pathtracer::material::UniformMaterial;
-    /// # use pathtracer::render::Object;
+    /// # use pathtracer::scene::Object;
     /// # use pathtracer::shape::Sphere;
     /// # use pathtracer::texture::UniformTexture;
     /// # use pathtracer::Point;

pathtracer/src/scene/scene.rs

@@ -0,0 +1,148 @@
+//! Scene representation.
+
+use super::{LightAggregate, Mesh, Object};
+use crate::core::{Camera, LinearColor};
+use beevee::bvh::BVH;
+use serde::Deserialize;
+
+/// Represent the scene being rendered.
+#[serde(from = "SerializedScene")]
+#[derive(Debug, PartialEq, Deserialize)]
+pub struct Scene {
+    pub(crate) camera: Camera,
+    pub(crate) lights: LightAggregate,
+    pub(crate) objects: Vec<Object>,
+    pub(crate) bvh: BVH,
+    pub(crate) background: LinearColor,
+    pub(crate) shot_rays: u32,
+    pub(crate) reflection_limit: u32,
+    pub(crate) diffraction_index: f32,
+}
+
+impl Scene {
+    /// Creates a new `Scene`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use pathtracer::core::{Camera, LightProperties, LinearColor};
+    /// # use pathtracer::material::UniformMaterial;
+    /// # use pathtracer::scene::{LightAggregate, Object, Scene};
+    /// # use pathtracer::shape::Sphere;
+    /// # use pathtracer::texture::UniformTexture;
+    /// # use pathtracer::Point;
+    /// #
+    /// let scene = Scene::new(
+    ///     Camera::default(),
+    ///     LightAggregate::empty(),
+    ///     vec![
+    ///         Object::new(
+    ///             Sphere::new(Point::origin(), 1.0).into(),
+    ///             UniformMaterial::new(
+    ///                 LightProperties::new(
+    ///                     LinearColor::new(1.0, 0.0, 0.0), // diffuse component
+    ///                     LinearColor::new(0.0, 0.0, 0.0), // specular component
+    ///                     None,
+    ///                 ),
+    ///             ).into(),
+    ///             UniformTexture::new(LinearColor::new(0.5, 0.5, 0.5)).into(),
+    ///         ),
+    ///     ],
+    ///     LinearColor::black(), // Background color
+    ///     5,   // amount of rays shot per pixel
+    ///     3,   // reflection recursion limit
+    ///     0.0, // diffraction index
+    /// );
+    /// ```
+    pub fn new(
+        camera: Camera,
+        lights: LightAggregate,
+        mut objects: Vec<Object>,
+        background: LinearColor,
+        shot_rays: u32,
+        reflection_limit: u32,
+        diffraction_index: f32,
+    ) -> Self {
+        let bvh = BVH::build(&mut objects);
+        Scene {
+            camera,
+            lights,
+            objects,
+            bvh,
+            background,
+            shot_rays,
+            reflection_limit,
+            diffraction_index,
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Deserialize)]
+#[serde(deny_unknown_fields)]
+struct SerializedScene {
+    camera: Camera,
+    #[serde(default)]
+    lights: LightAggregate,
+    #[serde(default)]
+    objects: Vec<Object>,
+    #[serde(default)]
+    meshes: Vec<Mesh>,
+    #[serde(default)]
+    background: LinearColor,
+    #[serde(default)]
+    shot_rays: u32,
+    #[serde(default)]
+    reflection_limit: u32,
+    #[serde(default = "crate::serialize::default_identity")]
+    starting_diffraction: f32,
+}
+
+impl From<SerializedScene> for Scene {
+    fn from(mut scene: SerializedScene) -> Self {
+        let mut flattened_meshes: Vec<Object> = scene
+            .meshes
+            .into_iter()
+            .map(|m| m.shapes)
+            .flatten()
+            .collect();
+        scene.objects.append(&mut flattened_meshes);
+
+        Scene::new(
+            scene.camera,
+            scene.lights,
+            scene.objects,
+            scene.background,
+            scene.shot_rays,
+            scene.reflection_limit,
+            scene.starting_diffraction,
+        )
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn deserialization_works() {
+        let yaml = std::include_str!("../../examples/scene.yaml");
+        let _: Scene = serde_yaml::from_str(yaml).unwrap();
+        // FIXME: actually test the equality ?
+    }
+
+    #[test]
+    fn empty_scene() {
+        use crate::core::Camera;
+        use crate::scene::{LightAggregate, Scene};
+
+        let _scene = Scene::new(
+            Camera::default(),
+            LightAggregate::empty(),
+            Vec::new(),           // Objects list
+            LinearColor::black(), // Background color
+            5,                    // aliasing limit
+            3,                    // reflection recursion limit
+            0.0,                  // diffraction index
+        );
+    }
+}

pathtracer/src/shape/interpolated_triangle.rs

@@ -0,0 +1,158 @@
+use super::triangle::Triangle;
+use super::Shape;
+use crate::{Point, Point2D, Vector};
+use beevee::aabb::{Bounded, AABB};
+use beevee::bvh::Intersected;
+use beevee::ray::Ray;
+use nalgebra::Unit;
+use serde::Deserialize;
+
+/// Represent a triangle with interpolated normals inside the scene.
+#[derive(Clone, Debug, PartialEq, Deserialize)]
+pub struct InterpolatedTriangle {
+    #[serde(flatten)]
+    tri: Triangle,
+    // FIXME: serialize with unit
+    normals: [Unit<Vector>; 3],
+}
+
+impl InterpolatedTriangle {
+    /// Creates a new `InterpolatedTriangle` from 3 [`Point`]s and 3 [`Vector`]s.
+    ///
+    /// [`Point`]: ../../type.Point.html
+    /// [`Point`]: ../../type.Vector.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use pathtracer::shape::InterpolatedTriangle;
+    /// # use pathtracer::{Point, Vector};
+    /// #
+    /// let t = InterpolatedTriangle::new(
+    ///     Point::new(1.0, 0.0, 0.0),
+    ///     Point::new(0.0, 1.0, 0.0),
+    ///     Point::new(0.0, 0.0, 1.0),
+    ///     Vector::x_axis(),
+    ///     Vector::y_axis(),
+    ///     Vector::z_axis(),
+    /// );
+    /// ```
+    pub fn new(
+        c0: Point,
+        c1: Point,
+        c2: Point,
+        n0: Unit<Vector>,
+        n1: Unit<Vector>,
+        n2: Unit<Vector>,
+    ) -> Self {
+        InterpolatedTriangle {
+            tri: Triangle::new(c0, c1, c2),
+            normals: [n0, n1, n2],
+        }
+    }
+}
+
+impl Shape for InterpolatedTriangle {
+    fn normal(&self, point: &Point) -> Unit<Vector> {
+        let (u, v) = {
+            let c = self.tri.barycentric(point);
+            (c.x, c.y)
+        };
+        let interpol = self.normals[0].as_ref() * (1. - u - v)
+            + self.normals[1].as_ref() * u
+            + self.normals[2].as_ref() * v;
+        Unit::new_normalize(interpol)
+    }
+
+    fn project_texel(&self, point: &Point) -> Point2D {
+        self.tri.project_texel(point)
+    }
+}
+
+impl Bounded for InterpolatedTriangle {
+    fn aabb(&self) -> AABB {
+        self.tri.aabb()
+    }
+
+    fn centroid(&self) -> Point {
+        self.tri.centroid()
+    }
+}
+
+impl Intersected for InterpolatedTriangle {
+    fn intersect(&self, ray: &Ray) -> Option<f32> {
+        self.tri.intersect(ray)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    fn simple_triangle() -> InterpolatedTriangle {
+        InterpolatedTriangle::new(
+            Point::origin(),
+            Point::new(0., 1., 1.),
+            Point::new(0., 1., 0.),
+            Vector::x_axis(),
+            Vector::y_axis(),
+            Vector::z_axis(),
+        )
+    }
+
+    #[test]
+    fn normal_interpolation_at_c0_works() {
+        let triangle = simple_triangle();
+        let normal = triangle.normal(&Point::origin());
+        assert_eq!(normal, Vector::x_axis());
+    }
+
+    #[test]
+    fn normal_interpolation_at_c1_works() {
+        let triangle = simple_triangle();
+        let normal = triangle.normal(&Point::new(0., 1., 1.));
+        assert_eq!(normal, Vector::y_axis());
+    }
+
+    #[test]
+    fn normal_interpolation_at_c2_works() {
+        let triangle = simple_triangle();
+        let normal = triangle.normal(&Point::new(0., 1., 0.));
+        assert_eq!(normal, Vector::z_axis());
+    }
+
+    #[test]
+    fn normal_interpolation_at_center_works() {
+        let triangle = simple_triangle();
+        let center = Point::new(0., 2. / 3., 1. / 3.);
+        let normal = triangle.normal(&center);
+        let expected = Unit::new_normalize(Vector::new(1., 1., 1.));
+        assert!((normal.as_ref() - expected.as_ref()).magnitude() < 1e-5)
+    }
+
+    #[test]
+    fn deserialization_works() {
+        let yaml = r#"
+            corners:
+              - [0.0, 0.0, 0.0]
+              - [0.0, 1.0, 1.0]
+              - [0.0, 1.0, 0.0]
+            normals:
+              - [1.0, 0.0, 0.0]
+              - [0.0, 1.0, 0.0]
+              - [0.0, 0.0, 1.0]
+        "#;
+        let triangle: InterpolatedTriangle = serde_yaml::from_str(yaml).unwrap();
+        assert_eq!(
+            triangle,
+            InterpolatedTriangle::new(
+                Point::origin(),
+                Point::new(0., 1., 1.),
+                Point::new(0., 1., 0.),
+                Vector::x_axis(),
+                Vector::y_axis(),
+                Vector::z_axis(),
+            )
+        )
+    }
+}

pathtracer/src/shape/mesh.rs

@@ -0,0 +1,9 @@
+use super::{InterpolatedTriangle, Shape, Triangle};
+use crate::material::{Material, TriangleMaterial, UniformMaterial};
+use crate::texture::{Texture, TriangleTexture, UniformTexture};
+use crate::Point;
+use beevee::{
+    aabb::{Bounded, AABB},
+    bvh::Intersected,
+    ray::Ray,
+};

pathtracer/src/shape/mod.rs

@@ -14,42 +14,53 @@ use serde::Deserialize;
 #[serde(rename_all = "lowercase")]
 #[allow(missing_docs)]
 #[enum_dispatch::enum_dispatch]
-#[derive(Debug, PartialEq, Deserialize)]
+#[derive(Debug, Clone, PartialEq, Deserialize)]
 pub enum ShapeEnum {
     Sphere,
     Triangle,
+    InterpolatedTriangle,
+}
+
+// FIXME: this has to be written by hand due to a limitation of `enum_dispatch` on super traits
+impl Bounded for ShapeEnum {
+    fn aabb(&self) -> AABB {
+        match self {
+            ShapeEnum::Sphere(s) => s.aabb(),
+            ShapeEnum::Triangle(s) => s.aabb(),
+            ShapeEnum::InterpolatedTriangle(s) => s.aabb(),
+        }
+    }
+
+    fn centroid(&self) -> Point {
+        match self {
+            ShapeEnum::Sphere(s) => s.centroid(),
+            ShapeEnum::Triangle(s) => s.centroid(),
+            ShapeEnum::InterpolatedTriangle(s) => s.centroid(),
+        }
+    }
+}
+
+impl Intersected for ShapeEnum {
+    fn intersect(&self, ray: &Ray) -> Option<f32> {
+        match self {
+            ShapeEnum::Sphere(s) => s.intersect(ray),
+            ShapeEnum::Triangle(s) => s.intersect(ray),
+            ShapeEnum::InterpolatedTriangle(s) => s.intersect(ray),
+        }
+    }
 }
 
 /// Represent an abstract shape inside the scene.
 #[enum_dispatch::enum_dispatch(ShapeEnum)]
-pub trait Shape: std::fmt::Debug {
-    /// Return the distance at which the object intersects with the ray, or None if it does not.
-    fn intersect(&self, ray: &Ray) -> Option<f32>;
+pub trait Shape: std::fmt::Debug + Intersected {
     /// Return the unit vector corresponding to the normal at this point of the shape.
     fn normal(&self, point: &Point) -> Unit<Vector>;
     /// Project the point from the shape's surface to its texel coordinates.
     fn project_texel(&self, point: &Point) -> Point2D;
-    /// Enclose the `Shape` in an axi-aligned bounding-box.
-    fn aabb(&self) -> AABB;
-    /// Return the centroid of the shape.
-    fn centroid(&self) -> Point;
 }
 
-impl Bounded for dyn Shape {
-    fn aabb(&self) -> AABB {
-        self.aabb()
-    }
-
-    fn centroid(&self) -> Point {
-        self.centroid()
-    }
-}
-
-impl Intersected for dyn Shape {
-    fn intersect(&self, ray: &Ray) -> Option<f32> {
-        self.intersect(ray)
-    }
-}
+mod interpolated_triangle;
+pub use interpolated_triangle::*;
 
 mod sphere;
 pub use sphere::*;

pathtracer/src/shape/sphere.rs

@@ -1,6 +1,7 @@
 use super::Shape;
 use crate::{Point, Point2D, Vector};
-use beevee::aabb::AABB;
+use beevee::aabb::{Bounded, AABB};
+use beevee::bvh::Intersected;
 use beevee::ray::Ray;
 use nalgebra::Unit;
 use serde::Deserialize;
@@ -38,6 +39,38 @@ impl Sphere {
 }
 
 impl Shape for Sphere {
+    fn normal(&self, point: &Point) -> Unit<Vector> {
+        let delt = if self.inverted {
+            self.center - point
+        } else {
+            point - self.center
+        };
+        Unit::new_normalize(delt)
+    }
+
+    fn project_texel(&self, point: &Point) -> Point2D {
+        // Project the sphere on the XY-plane
+        Point2D::new(
+            0.5 + (point.x - self.center.x) / (2. * self.radius),
+            0.5 + (point.y - self.center.y) / (2. * self.radius),
+        )
+    }
+}
+
+impl Bounded for Sphere {
+    fn aabb(&self) -> AABB {
+        let delt = Vector::new(self.radius, self.radius, self.radius);
+        let min = self.center - delt;
+        let max = self.center + delt;
+        AABB::with_bounds(min, max)
+    }
+
+    fn centroid(&self) -> Point {
+        self.center
+    }
+}
+
+impl Intersected for Sphere {
     fn intersect(&self, ray: &Ray) -> Option<f32> {
         use std::mem;
 
@@ -67,34 +100,6 @@ impl Shape for Sphere {
             Some(t_0)
         }
     }
-
-    fn normal(&self, point: &Point) -> Unit<Vector> {
-        let delt = if self.inverted {
-            self.center - point
-        } else {
-            point - self.center
-        };
-        Unit::new_normalize(delt)
-    }
-
-    fn project_texel(&self, point: &Point) -> Point2D {
-        // Project the sphere on the XY-plane
-        Point2D::new(
-            0.5 + (point.x - self.center.x) / (2. * self.radius),
-            0.5 + (point.y - self.center.y) / (2. * self.radius),
-        )
-    }
-
-    fn aabb(&self) -> AABB {
-        let delt = Vector::new(self.radius, self.radius, self.radius);
-        let min = self.center - delt;
-        let max = self.center + delt;
-        AABB::with_bounds(min, max)
-    }
-
-    fn centroid(&self) -> Point {
-        self.center
-    }
 }
 
 #[cfg(test)]

pathtracer/src/shape/triangle.rs

@@ -1,12 +1,14 @@
 use super::Shape;
 use crate::{Point, Point2D, Vector};
-use beevee::aabb::AABB;
+use beevee::aabb::{Bounded, AABB};
+use beevee::bvh::Intersected;
 use beevee::ray::Ray;
 use nalgebra::Unit;
-use serde::{Deserialize, Deserializer};
+use serde::Deserialize;
 
 /// Represent a triangle inside the scene.
-#[derive(Clone, Debug, PartialEq)]
+#[serde(from = "SerializedTriangle")]
+#[derive(Clone, Debug, PartialEq, Deserialize)]
 pub struct Triangle {
     c0: Point,
     c0c1: Vector,
@@ -38,7 +40,7 @@ impl Triangle {
         }
     }
 
-    fn barycentric(&self, point: &Point) -> Point2D {
+    pub(crate) fn barycentric(&self, point: &Point) -> Point2D {
         let c0_pos = point - self.c0;
         // P - A  =  u * (B - A) + v * (C - A)
         // (C - A) = v0 is c0c2
@@ -58,6 +60,29 @@ impl Triangle {
 }
 
 impl Shape for Triangle {
+    fn normal(&self, _: &Point) -> Unit<Vector> {
+        Unit::new_normalize(self.c0c1.cross(&self.c0c2))
+    }
+
+    fn project_texel(&self, point: &Point) -> Point2D {
+        self.barycentric(point)
+    }
+}
+
+impl Bounded for Triangle {
+    fn aabb(&self) -> AABB {
+        AABB::empty()
+            .grow(&self.c0)
+            .grow(&(self.c0 + self.c0c1))
+            .grow(&(self.c0 + self.c0c2))
+    }
+
+    fn centroid(&self) -> Point {
+        self.c0 + (self.c0c1 + self.c0c2) / 2.
+    }
+}
+
+impl Intersected for Triangle {
     fn intersect(&self, ray: &Ray) -> Option<f32> {
         let pvec = ray.direction.cross(&self.c0c2);
         let det = self.c0c1.dot(&pvec);
@@ -88,25 +113,6 @@ impl Shape for Triangle {
             Some(t)
         }
     }
-
-    fn normal(&self, _: &Point) -> Unit<Vector> {
-        Unit::new_normalize(self.c0c1.cross(&self.c0c2))
-    }
-
-    fn project_texel(&self, point: &Point) -> Point2D {
-        self.barycentric(point)
-    }
-
-    fn aabb(&self) -> AABB {
-        AABB::empty()
-            .grow(&self.c0)
-            .grow(&(self.c0 + self.c0c1))
-            .grow(&(self.c0 + self.c0c2))
-    }
-
-    fn centroid(&self) -> Point {
-        self.c0 + (self.c0c1 + self.c0c2) / 2.
-    }
 }
 
 #[derive(Debug, Deserialize)]
@@ -124,16 +130,6 @@ impl From<SerializedTriangle> for Triangle {
     }
 }
 
-impl<'de> Deserialize<'de> for Triangle {
-    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
-    where
-        D: Deserializer<'de>,
-    {
-        let cam: SerializedTriangle = Deserialize::deserialize(deserializer)?;
-        Ok(cam.into())
-    }
-}
-
 #[cfg(test)]
 mod test {
     use super::*;

pathtracer/src/texture/mod.rs

@@ -9,10 +9,11 @@ use serde::Deserialize;
 #[serde(rename_all = "lowercase")]
 #[allow(missing_docs)]
 #[enum_dispatch::enum_dispatch]
-#[derive(Debug, PartialEq, Deserialize)]
+#[derive(Debug, Clone, PartialEq, Deserialize)]
 pub enum TextureEnum {
     #[serde(rename = "uniform")]
     UniformTexture,
+    TriangleTexture,
 }
 
 /// Represent an object's texture.
@@ -22,5 +23,8 @@ pub trait Texture: std::fmt::Debug {
     fn texel_color(&self, point: Point2D) -> LinearColor;
 }
 
+mod triangle;
+pub use triangle::*;
+
 mod uniform;
 pub use uniform::*;

pathtracer/src/texture/triangle.rs

@@ -0,0 +1,23 @@
+use super::{uniform::UniformTexture, Texture};
+use crate::core::LinearColor;
+use crate::Point2D;
+use serde::Deserialize;
+
+/// Represent a texture which interpolates between three points.
+#[derive(Debug, Clone, PartialEq, Deserialize)]
+pub struct TriangleTexture {
+    /// The texture at each point
+    textures: [UniformTexture; 3],
+}
+
+impl Texture for TriangleTexture {
+    fn texel_color(&self, point: Point2D) -> LinearColor {
+        let (u, v) = (point.x, point.y);
+        let sum = self.textures[0].texel_color(point) * (1. - u - v)
+            + self.textures[1].texel_color(point) * u
+            + self.textures[2].texel_color(point) * v;
+        sum / 3.
+    }
+}
+
+// FIXME: tests