Refactored to improve some performance.

1. Removed duplication to increase performance a little bit
2. Fixed some minor rendering related issues
3. Added a Defocus Blur Demo

src/camera.rs

@@ -1,10 +1,19 @@
-use crate::types::{Ray, Vec3};
+use {
+    crate::types::{Ray, Vec3},
+    rand::Rng,
+};
 
 pub struct Camera {
-    pub origin: Vec3,
+    origin: Vec3,
-    pub horizontal: Vec3,
+    horizontal: Vec3,
-    pub vertical: Vec3,
+    vertical: Vec3,
-    pub lower_left_corner: Vec3,
+    lower_left_corner: Vec3,
+    lens_radius: f64,
+
+    // position vectors
+    u: Vec3,
+    v: Vec3,
+    w: Vec3,
 }
 
 impl Camera {
@@ -13,7 +22,15 @@ impl Camera {
     // look_at is the point where camera is looking
     // v_up is camera's up vector. i.e. it points upwards from the camera
     // orthogonal to look_from - look_at vector
-    pub fn new(look_from: Vec3, look_at: Vec3, v_up: Vec3, vertical_fov: f64, aspect: f64) -> Self {
+    pub fn new(
+        look_from: Vec3,
+        look_at: Vec3,
+        v_up: Vec3,
+        vertical_fov: f64,
+        aspect: f64,
+        aperture: f64,
+        focus_distance: f64,
+    ) -> Self {
         // convert degree to radian
         let angle = vertical_fov * std::f64::consts::PI / 180.0;
         let half_height = (angle / 2.0).tan();
@@ -24,35 +41,42 @@ impl Camera {
         let u = v_up.cross(&w).unit_vector();
         let v = w.cross(&u);
 
-        let lower_left_corner = origin - u * half_width - v * half_height - w;
+        let lower_left_corner = origin
+            - u * focus_distance * half_width
+            - v * focus_distance * half_height
+            - w * focus_distance;
         let horizontal = u * half_width * 2.0;
         let vertical = v * half_height * 2.0;
+        let lens_radius = aperture / 2.0;
 
         Self {
+            lens_radius,
             lower_left_corner,
             horizontal,
             vertical,
             origin,
+            u,
+            v,
+            w,
         }
     }
 
     pub fn get_ray(&self, u: f64, v: f64) -> Ray {
+        let mut rng = rand::thread_rng();
+        let rd = random_in_unit_disk(&mut rng) * self.lens_radius;
+        let offset = self.u * rd.x() + self.v * rd.y();
         Ray::new(
-            self.origin,
+            self.origin + offset,
-            self.lower_left_corner + self.horizontal * u + self.vertical * v - self.origin,
+            self.lower_left_corner + self.horizontal * u + self.vertical * v - self.origin - offset,
         )
     }
 }
 
-impl std::default::Default for Camera {
+fn random_in_unit_disk(rng: &mut rand::rngs::ThreadRng) -> Vec3 {
-    fn default() -> Self {
+    let mut p = Vec3::new(rng.gen::<f64>(), rng.gen::<f64>(), 0.0) * 2.0 - Vec3::new(1.0, 0.0, 0.0);
-        Camera::new(
+
-            Vec3::new(0.0, 0.0, 0.0),
+    while p.dot(&p) >= 1.0 {
-            Vec3::new(0.0, 0.0, -1.0),
+        p = Vec3::new(rng.gen::<f64>(), rng.gen::<f64>(), 0.0) * 2.0 - Vec3::new(1.0, 0.0, 0.0);
-            Vec3::new(0.0, 1.0, 0.0),
-            90.0,
-            // 2:1 aspect ratio width:height
-            2.0,
-        )
     }
+    p
 }

src/demos/defocus_blur.rs

@@ -0,0 +1,125 @@
+use {
+    crate::{
+        demos::{Chunk, Demo},
+        types::{
+            material::{Dielectric, Lambertian, Metal},
+            Hitable, HitableList, Ray, Sphere, Vec3,
+        },
+        Camera,
+    },
+    rand::Rng,
+};
+
+pub struct DefocusBlur;
+
+impl Demo for DefocusBlur {
+    fn name(&self) -> &'static str {
+        "defocus-blur"
+    }
+
+    fn world(&self) -> Option<HitableList> {
+        let radius = (std::f64::consts::PI / 4.0).cos();
+        Some(HitableList {
+            list: vec![
+                Box::new(Sphere::with_material(
+                    Vec3::new(-radius, 0.0, -1.0),
+                    radius,
+                    Box::new(Lambertian::new(Vec3::new(0.0, 0.0, 1.0))),
+                )),
+                Box::new(Sphere::with_material(
+                    Vec3::new(radius, 0.0, -1.0),
+                    radius,
+                    Box::new(Metal::with_fuzz(Vec3::new(0.5, 0.5, 0.0), 0.2)),
+                )),
+                Box::new(Sphere::with_material(
+                    Vec3::new(-3.0 * radius, 0.0, -1.0),
+                    radius,
+                    Box::new(Dielectric::new(1.5)),
+                )),
+                Box::new(Sphere::with_material(
+                    Vec3::new(0.0, -100.5, -1.0),
+                    100.0,
+                    Box::new(Lambertian::new(Vec3::new(0.8, 0.8, 0.0))),
+                )),
+            ],
+        })
+    }
+
+    fn camera(&self, aspect_ratio: f64) -> Option<Camera> {
+        let lookfrom = Vec3::new(3.0, 3.0, 2.0);
+        let lookat = Vec3::new(0.0, 0.0, -1.0);
+        let aperture = 2.0;
+        let distance_to_focus = (lookfrom - lookat).length();
+        let camera = Camera::new(
+            lookfrom,
+            lookat,
+            Vec3::new(0.0, 1.0, 0.0),
+            20.0,
+            aspect_ratio,
+            aperture,
+            distance_to_focus,
+        );
+        Some(camera)
+    }
+
+    fn render_chunk(
+        &self,
+        chunk: &mut Chunk,
+        camera: Option<&Camera>,
+        world: Option<&HitableList>,
+        samples: u8,
+    ) {
+        let x = chunk.x;
+        let y = chunk.y;
+        let nx = chunk.nx;
+        let ny = chunk.ny;
+        let start_x = chunk.start_x;
+        let start_y = chunk.start_y;
+        let buffer = &mut chunk.buffer;
+        let camera = camera.unwrap();
+        let world = world.unwrap();
+
+        let mut rng = rand::thread_rng();
+        let mut offset = 0;
+
+        for j in start_y..start_y + ny {
+            for i in start_x..start_x + nx {
+                let mut color = Vec3::new(0.0, 0.0, 0.0);
+                for _s in 0..samples {
+                    let u = (i as f64 + rng.gen::<f64>()) / x as f64;
+                    let v = (j as f64 + rng.gen::<f64>()) / y as f64;
+
+                    let ray = camera.get_ray(u, v);
+                    color += calc_color(ray, &world, 0);
+                }
+
+                color /= samples as f64;
+
+                // gamma 2 corrected
+                buffer[offset] = (255.99 * color.r().sqrt()) as u8;
+                buffer[offset + 1] = (255.99 * color.g().sqrt()) as u8;
+                buffer[offset + 2] = (255.99 * color.b().sqrt()) as u8;
+                offset += 4;
+            }
+        }
+    }
+}
+
+fn calc_color(ray: Ray, world: &HitableList, depth: u32) -> Vec3 {
+    if let Some(hit_rec) = world.hit(&ray, 0.001, std::f64::MAX) {
+        if depth >= 50 {
+            Vec3::new(0.0, 0.0, 0.0)
+        } else {
+            let material = hit_rec.material.as_ref();
+            if let (attenuation, Some(scattered_ray)) = material.unwrap().scatter(&ray, &hit_rec) {
+                calc_color(scattered_ray, &world, depth + 1) * attenuation
+            } else {
+                Vec3::new(0.0, 0.0, 0.0)
+            }
+        }
+    } else {
+        let unit_direction = ray.direction().unit_vector();
+        let t = 0.5 * (unit_direction.y() + 1.0);
+        Vec3::new(1.0, 1.0, 1.0) * (1.0 - t) + Vec3::new(0.5, 0.7, 1.0) * t
+    }
+}

src/demos/dielectric_material.rs

@@ -17,16 +17,8 @@ impl Demo for DielectricMaterial {
         "dielectric-material"
     }
 
-    fn render_chunk(&self, chunk: &mut Chunk, samples: u8) {
+    fn world(&self) -> Option<HitableList> {
-        let x = chunk.x;
+        Some(HitableList {
-        let y = chunk.y;
-        let nx = chunk.nx;
-        let ny = chunk.ny;
-        let start_x = chunk.start_x;
-        let start_y = chunk.start_y;
-        let buffer = &mut chunk.buffer;
-
-        let world = HitableList {
             list: vec![
                 Box::new(Sphere::with_material(
                     Vec3::new(0.0, 0.0, -1.0),
@@ -54,9 +46,26 @@ impl Demo for DielectricMaterial {
                     Box::new(Dielectric::new(1.5)),
                 )),
             ],
-        };
+        })
+    }
+
+    fn render_chunk(
+        &self,
+        chunk: &mut Chunk,
+        camera: Option<&Camera>,
+        world: Option<&HitableList>,
+        samples: u8,
+    ) {
+        let x = chunk.x;
+        let y = chunk.y;
+        let nx = chunk.nx;
+        let ny = chunk.ny;
+        let start_x = chunk.start_x;
+        let start_y = chunk.start_y;
+        let buffer = &mut chunk.buffer;
+        let camera = camera.unwrap();
+        let world = world.unwrap();
 
-        let camera: Camera = Default::default();
         let mut rng = rand::thread_rng();
         let mut offset = 0;
 

src/demos/diffuse_materials.rs

@@ -14,7 +14,22 @@ impl Demo for DiffuseMaterials {
         "diffuse-materials"
     }
 
-    fn render_chunk(&self, chunk: &mut Chunk, samples: u8) {
+    fn world(&self) -> Option<HitableList> {
+        Some(HitableList {
+            list: vec![
+                Box::new(Sphere::new(Vec3::new(0.0, 0.0, -1.0), 0.5)),
+                Box::new(Sphere::new(Vec3::new(0.0, -100.5, -1.0), 100.0)),
+            ],
+        })
+    }
+
+    fn render_chunk(
+        &self,
+        chunk: &mut Chunk,
+        camera: Option<&Camera>,
+        world: Option<&HitableList>,
+        samples: u8,
+    ) {
         let x = chunk.x;
         let y = chunk.y;
         let nx = chunk.nx;
@@ -22,15 +37,9 @@ impl Demo for DiffuseMaterials {
         let start_x = chunk.start_x;
         let start_y = chunk.start_y;
         let buffer = &mut chunk.buffer;
+        let camera = camera.unwrap();
+        let world = world.unwrap();
 
-        let world = HitableList {
-            list: vec![
-                Box::new(Sphere::new(Vec3::new(0.0, 0.0, -1.0), 0.5)),
-                Box::new(Sphere::new(Vec3::new(0.0, -100.5, -1.0), 100.0)),
-            ],
-        };
-
-        let camera: Camera = Default::default();
         let mut rng = rand::thread_rng();
         let mut offset = 0;
         for j in start_y..start_y + ny {

src/demos/hitable_sphere.rs

@@ -1,6 +1,7 @@
 use crate::{
     demos::{Chunk, Demo},
     types::{Hitable, HitableList, Ray, Sphere, Vec3},
+    Camera,
 };
 pub struct HitableSphere;
 
@@ -9,7 +10,22 @@ impl Demo for HitableSphere {
         "sphere-using-hit-table"
     }
 
-    fn render_chunk(&self, chunk: &mut Chunk, _samples: u8) {
+    fn world(&self) -> Option<HitableList> {
+        Some(HitableList {
+            list: vec![
+                Box::new(Sphere::new(Vec3::new(0.0, 0.0, -1.0), 0.5)),
+                Box::new(Sphere::new(Vec3::new(0.0, -100.5, -1.0), 100.0)),
+            ],
+        })
+    }
+
+    fn render_chunk(
+        &self,
+        chunk: &mut Chunk,
+        _camera: Option<&Camera>,
+        world: Option<&HitableList>,
+        _samples: u8,
+    ) {
         let x = chunk.x;
         let y = chunk.y;
         let nx = chunk.nx;
@@ -17,18 +33,13 @@ impl Demo for HitableSphere {
         let start_x = chunk.start_x;
         let start_y = chunk.start_y;
         let buffer = &mut chunk.buffer;
+        let world = world.unwrap();
 
         let lower_left_corner = Vec3::new(-2.0, -1.0, -1.0);
         let horizontal = Vec3::new(4.0, 0.0, 0.0);
         let vertical = Vec3::new(0.0, 2.0, 0.0);
         let origin = Vec3::new(0.0, 0.0, 0.0);
 
-        let world = HitableList {
-            list: vec![
-                Box::new(Sphere::new(Vec3::new(0.0, 0.0, -1.0), 0.5)),
-                Box::new(Sphere::new(Vec3::new(0.0, -100.5, -1.0), 100.0)),
-            ],
-        };
         let mut offset = 0;
         for j in start_y..start_y + ny {
             for i in start_x..start_x + nx {

src/demos/linear_gradient_rectangle.rs

@@ -1,7 +1,8 @@
 pub struct LinearGradientRectangle;
 
 use crate::{
-    types::{Ray, Vec3},
+    types::{HitableList, Ray, Vec3},
+    Camera,
     {demos::Chunk, Demo},
 };
 
@@ -10,7 +11,13 @@ impl Demo for LinearGradientRectangle {
         "linear-gradient-rectangle"
     }
 
-    fn render_chunk(&self, chunk: &mut Chunk, _samples: u8) {
+    fn render_chunk(
+        &self,
+        chunk: &mut Chunk,
+        _camera: Option<&Camera>,
+        _world: Option<&HitableList>,
+        _samples: u8,
+    ) {
         let x = chunk.x;
         let y = chunk.y;
         let nx = chunk.nx;

src/demos/materials.rs

@@ -17,16 +17,8 @@ impl Demo for Materials {
         "metal-material"
     }
 
-    fn render_chunk(&self, chunk: &mut Chunk, samples: u8) {
+    fn world(&self) -> Option<HitableList> {
-        let x = chunk.x;
+        Some(HitableList {
-        let y = chunk.y;
-        let nx = chunk.nx;
-        let ny = chunk.ny;
-        let start_x = chunk.start_x;
-        let start_y = chunk.start_y;
-        let buffer = &mut chunk.buffer;
-
-        let world = HitableList {
             list: vec![
                 Box::new(Sphere::with_material(
                     Vec3::new(0.0, 0.0, -1.0),
@@ -49,9 +41,25 @@ impl Demo for Materials {
                     Box::new(Metal::with_fuzz(Vec3::new(0.8, 0.8, 0.8), 0.5)),
                 )),
             ],
-        };
+        })
+    }
+
+    fn render_chunk(
+        &self,
+        chunk: &mut Chunk,
+        camera: Option<&Camera>,
+        world: Option<&HitableList>,
+        samples: u8,
+    ) {
+        let x = chunk.x;
+        let y = chunk.y;
+        let nx = chunk.nx;
+        let ny = chunk.ny;
+        let start_x = chunk.start_x;
+        let start_y = chunk.start_y;
+        let buffer = &mut chunk.buffer;
+        let camera = camera.unwrap();
 
-        let camera: Camera = Default::default();
         let mut rng = rand::thread_rng();
         let mut offset = 0;
 
@@ -63,7 +71,7 @@ impl Demo for Materials {
                     let v = (j as f64 + rng.gen::<f64>()) / y as f64;
 
                     let ray = camera.get_ray(u, v);
-                    color += calc_color(ray, &world, 0);
+                    color += calc_color(ray, world.unwrap(), 0);
                 }
 
                 color /= samples as f64;

src/demos/mod.rs

@@ -1,3 +1,4 @@
+mod defocus_blur;
 mod dielectric_material;
 mod diffuse_materials;
 mod hitable_sphere;
@@ -9,6 +10,7 @@ mod simple_rectangle;
 mod simple_sphere;
 mod surface_normal_sphere;
 
+pub use defocus_blur::DefocusBlur;
 pub use dielectric_material::DielectricMaterial;
 pub use diffuse_materials::DiffuseMaterials;
 pub use hitable_sphere::HitableSphere;
@@ -21,7 +23,10 @@ pub use simple_sphere::SimpleSphere;
 pub use surface_normal_sphere::SurfaceNormalSphere;
 
 use {
-    crate::{HORIZONTAL_PARTITION, VERTICAL_PARTITION},
+    crate::{
+        types::{HitableList, Vec3},
+        Camera, HORIZONTAL_PARTITION, VERTICAL_PARTITION,
+    },
     rayon::prelude::*,
     std::{
         fs::File,
@@ -45,14 +50,14 @@ pub trait Demo: std::marker::Sync {
     fn render(&self, buf: &mut Vec<u8>, width: usize, height: usize, samples: u8) {
         let nx = width / VERTICAL_PARTITION;
         let ny = height / HORIZONTAL_PARTITION;
+        let world = self.world();
+        let camera = self.camera(nx as f64 / ny as f64);
 
         let buf = Arc::new(Mutex::new(buf));
 
-        (0..VERTICAL_PARTITION).into_par_iter().for_each(move |j| {
+        (0..VERTICAL_PARTITION).into_par_iter().for_each(|j| {
             let buf = buf.clone();
-            (0..HORIZONTAL_PARTITION)
+            (0..HORIZONTAL_PARTITION).into_par_iter().for_each(|i| {
-                .into_par_iter()
-                .for_each(move |i| {
                 let start_y = j * ny;
                 let start_x = i * nx;
                 let x = width;
@@ -66,7 +71,7 @@ pub trait Demo: std::marker::Sync {
                     start_y,
                     buffer: vec![0; nx * ny * 4],
                 };
-                    self.render_chunk(&mut chunk, samples);
+                self.render_chunk(&mut chunk, camera.as_ref(), world.as_ref(), samples);
 
                 let mut buf = buf.lock().unwrap();
 
@@ -83,7 +88,31 @@ pub trait Demo: std::marker::Sync {
         });
     }
 
-    fn render_chunk(&self, chunk: &mut Chunk, samples: u8);
+    fn world(&self) -> Option<HitableList> {
+        None
+    }
+
+    fn camera(&self, aspect_ratio: f64) -> Option<Camera> {
+        let lookfrom = Vec3::new(0.0, 0.0, 0.0);
+        let lookat = Vec3::new(0.0, 0.0, -1.0);
+        Some(Camera::new(
+            lookfrom,
+            lookat,
+            Vec3::new(0.0, 1.0, 0.0),
+            90.0,
+            aspect_ratio,
+            0.0,
+            1.0,
+        ))
+    }
+
+    fn render_chunk(
+        &self,
+        chunk: &mut Chunk,
+        camera: Option<&Camera>,
+        world: Option<&HitableList>,
+        samples: u8,
+    );
 
     fn name(&self) -> &'static str;
 

src/demos/positionable_camera.rs

@@ -17,17 +17,9 @@ impl Demo for PositionableCamera {
         "positionable-camera"
     }
 
-    fn render_chunk(&self, chunk: &mut Chunk, samples: u8) {
+    fn world(&self) -> Option<HitableList> {
-        let x = chunk.x;
-        let y = chunk.y;
-        let nx = chunk.nx;
-        let ny = chunk.ny;
-        let start_x = chunk.start_x;
-        let start_y = chunk.start_y;
-        let buffer = &mut chunk.buffer;
         let radius = (std::f64::consts::PI / 4.0).cos();
-
+        Some(HitableList {
-        let world = HitableList {
             list: vec![
                 Box::new(Sphere::with_material(
                     Vec3::new(-radius, 0.0, -1.0),
@@ -50,15 +42,39 @@ impl Demo for PositionableCamera {
                     Box::new(Lambertian::new(Vec3::new(0.8, 0.8, 0.0))),
                 )),
             ],
-        };
+        })
+    }
 
-        let camera = Camera::new(
+    fn camera(&self, aspect_ratio: f64) -> Option<Camera> {
-            Vec3::new(-2.0, 2.0, 1.0),
+        let lookfrom = Vec3::new(-2.0, 2.0, 1.0);
-            Vec3::new(0.0, 0.0, -1.0),
+        let lookat = Vec3::new(0.0, 0.0, -1.0);
+        Some(Camera::new(
+            lookfrom,
+            lookat,
             Vec3::new(0.0, 1.0, 0.0),
             68.0,
-            nx as f64 / ny as f64,
+            aspect_ratio,
-        );
+            0.0,
+            1.0,
+        ))
+    }
+
+    fn render_chunk(
+        &self,
+        chunk: &mut Chunk,
+        camera: Option<&Camera>,
+        world: Option<&HitableList>,
+        samples: u8,
+    ) {
+        let x = chunk.x;
+        let y = chunk.y;
+        let nx = chunk.nx;
+        let ny = chunk.ny;
+        let start_x = chunk.start_x;
+        let start_y = chunk.start_y;
+        let buffer = &mut chunk.buffer;
+        let camera = camera.unwrap();
+        let world = world.unwrap();
         let mut rng = rand::thread_rng();
         let mut offset = 0;
 
@@ -72,9 +88,7 @@ impl Demo for PositionableCamera {
                     let ray = camera.get_ray(u, v);
                     color += calc_color(ray, &world, 0);
                 }
-
                 color /= samples as f64;
-
                 // gamma 2 corrected
                 buffer[offset] = (255.99 * color.r().sqrt()) as u8;
                 buffer[offset + 1] = (255.99 * color.g().sqrt()) as u8;

src/demos/simple_antialiasing.rs

@@ -12,7 +12,23 @@ impl Demo for SimpleAntialiasing {
     fn name(&self) -> &'static str {
         "simple-antialiasing"
     }
-    fn render_chunk(&self, chunk: &mut Chunk, samples: u8) {
+
+    fn world(&self) -> Option<HitableList> {
+        Some(HitableList {
+            list: vec![
+                Box::new(Sphere::new(Vec3::new(0.0, 0.0, -1.0), 0.5)),
+                Box::new(Sphere::new(Vec3::new(0.0, -100.5, -1.0), 100.0)),
+            ],
+        })
+    }
+
+    fn render_chunk(
+        &self,
+        chunk: &mut Chunk,
+        camera: Option<&Camera>,
+        world: Option<&HitableList>,
+        samples: u8,
+    ) {
         let x = chunk.x;
         let y = chunk.y;
         let nx = chunk.nx;
@@ -20,15 +36,8 @@ impl Demo for SimpleAntialiasing {
         let start_x = chunk.start_x;
         let start_y = chunk.start_y;
         let buffer = &mut chunk.buffer;
+        let camera = camera.unwrap();
 
-        let world = HitableList {
-            list: vec![
-                Box::new(Sphere::new(Vec3::new(0.0, 0.0, -1.0), 0.5)),
-                Box::new(Sphere::new(Vec3::new(0.0, -100.5, -1.0), 100.0)),
-            ],
-        };
-
-        let camera: Camera = Default::default();
         let mut rng = rand::thread_rng();
         let mut offset = 0;
 
@@ -40,7 +49,7 @@ impl Demo for SimpleAntialiasing {
                     let v = (j as f64 + rng.gen::<f64>()) / y as f64;
 
                     let r = camera.get_ray(u, v);
-                    color += calc_color(r, &world);
+                    color += calc_color(r, world.unwrap());
                 }
                 color /= samples as f64;
                 buffer[offset] = (255.99 * color.r()) as u8;

src/demos/simple_rectangle.rs

@@ -1,4 +1,8 @@
-use crate::demos::{Chunk, Demo};
+use crate::{
+    demos::{Chunk, Demo},
+    types::HitableList,
+    Camera,
+};
 
 pub struct SimpleRectangle;
 
@@ -7,7 +11,13 @@ impl Demo for SimpleRectangle {
         "simple_rectangle"
     }
 
-    fn render_chunk(&self, chunk: &mut Chunk, _samples: u8) {
+    fn render_chunk(
+        &self,
+        chunk: &mut Chunk,
+        _camera: Option<&Camera>,
+        _world: Option<&HitableList>,
+        _samples: u8,
+    ) {
         let x = chunk.x;
         let y = chunk.y;
         let nx = chunk.nx;

src/demos/simple_sphere.rs

@@ -1,6 +1,7 @@
 use crate::{
     demos::{Chunk, Demo},
-    types::{Ray, Vec3},
+    types::{HitableList, Ray, Vec3},
+    Camera,
 };
 
 const RADIUS: f64 = 0.5;
@@ -12,7 +13,13 @@ impl Demo for SimpleSphere {
         "simple_sphere"
     }
 
-    fn render_chunk(&self, chunk: &mut Chunk, _samples: u8) {
+    fn render_chunk(
+        &self,
+        chunk: &mut Chunk,
+        _camera: Option<&Camera>,
+        _world: Option<&HitableList>,
+        _samples: u8,
+    ) {
         let x = chunk.x;
         let y = chunk.y;
         let nx = chunk.nx;

src/demos/surface_normal_sphere.rs

@@ -1,6 +1,7 @@
 use crate::{
     demos::{Chunk, Demo},
-    types::{Ray, Vec3},
+    types::{HitableList, Ray, Vec3},
+    Camera,
 };
 
 const RADIUS: f64 = 0.5;
@@ -11,7 +12,13 @@ impl Demo for SurfaceNormalSphere {
         "surface_normal_sphere"
     }
 
-    fn render_chunk(&self, chunk: &mut Chunk, _samples: u8) {
+    fn render_chunk(
+        &self,
+        chunk: &mut Chunk,
+        _camera: Option<&Camera>,
+        _world: Option<&HitableList>,
+        _samples: u8,
+    ) {
         let x = chunk.x;
         let y = chunk.y;
         let nx = chunk.nx;

src/main.rs

@@ -80,6 +80,7 @@ fn main() -> Result<(), String> {
                         Some(Keycode::Num8) => active_demo = Box::new(demos::Materials),
                         Some(Keycode::Num9) => active_demo = Box::new(demos::DielectricMaterial),
                         Some(Keycode::Num0) => active_demo = Box::new(demos::PositionableCamera),
+                        Some(Keycode::Minus) => active_demo = Box::new(demos::DefocusBlur),
                         None => unreachable!(),
                         _ => (),
                     };

src/types/hitable.rs

@@ -21,7 +21,7 @@ pub struct HitRecord<'a> {
     pub material: Option<&'a Box<dyn Material>>,
 }
 
-pub trait Hitable {
+pub trait Hitable: Send + Sync {
     fn hit(&self, _ray: &Ray, _t_min: f64, _t_max: f64) -> Option<HitRecord> {
         None
     }

src/types/material.rs

@@ -3,7 +3,7 @@ use {
     rand::Rng,
 };
 
-pub trait Material {
+pub trait Material: Send + Sync {
     fn scatter(&self, ray: &Ray, hit_rec: &HitRecord) -> (Vec3, Option<Ray>);
 }
 
@@ -106,7 +106,8 @@ impl Material for Dielectric {
     }
 }
 
-// Polynomial approximation to figure out reflectivity as the angle changes
+// Christophe Schlick's Polynomial approximation to figure out reflectivity as the angle changes
+// See Fresnel Equations, https://en.wikipedia.org/wiki/Fresnel_equations
 fn schlick(cosine: f64, reflection_index: f64) -> f64 {
     let mut r0 = (1.0 - reflection_index) / (1.0 + reflection_index);
     r0 = r0 * r0;