Feat: Materials!

Got the enums to work. This match block is going to be absolutely
massive, but whatever. Current materials are Lambertian and Metal.

src/hittable.rs

@@ -2,12 +2,11 @@
 use crate::vec3::Vec3;
 use crate::ray::Ray;
 use crate::material::Material;
-use std::rc::Rc;
 
 pub struct HitRecord{
     pub p: Vec3,
     pub normal: Vec3,
-    pub material: Option<Rc<dyn Material>>,
+    pub material: Option<Material>,
     pub t: f32,
     pub front_face: bool,
 }

src/main.rs

@@ -14,6 +14,7 @@ use crate::hittable::{
     Hittable,
     HittableList,
 };
+use crate::material::Material;
 
 use crate::camera::Camera;
 use rand::{Rng, SeedableRng};
@@ -32,25 +33,52 @@ fn main() {
     
     // world
 
+    let mat_ground = Material::Lambertian{ albedo: Vec3::new(0.8, 0.8, 0.0) };
+    let mat_center = Material::Lambertian{ albedo: Vec3::new(0.7, 0.3, 0.3) };
+    let mat_left   = Material::Metal{ albedo: Vec3::new(0.8, 0.8, 0.8) };
+    let mat_right  = Material::Metal{ albedo: Vec3::new(0.8, 0.6, 0.2) };
+
     let mut world = HittableList::new();
-    world.add(
-        Box::new(
-            Sphere{
-                center: Vec3{ x: 0.0, y: 0.0, z: -1.0},
-                radius: 0.5,
-                material: None,
-            }
-        )
-    );
     world.add(
         Box::new(
             Sphere{
                 center: Vec3{ x: 0.0, y: -100.5, z: -1.0 },
                 radius: 100.0,
-                material: None,
+                material: Some(mat_ground),
             }
         )
     );
+
+    world.add(
+        Box::new(
+            Sphere{
+                center: Vec3{ x: 0.0, y: 0.0, z: -1.0},
+                radius: 0.5,
+                material: Some(mat_center),
+            }
+        )
+    );
+
+    world.add(
+        Box::new(
+            Sphere{
+                center: Vec3::new(-1.0, 0.0, -1.0),
+                radius: 0.5,
+                material: Some(mat_left),
+            }
+        )
+    );
+    
+    world.add(
+        Box::new(
+            Sphere{
+                center: Vec3::new( 1.0, 0.0, -1.0),
+                radius: 0.5,
+                material: Some(mat_right),
+            }
+        )
+    );
+
     // camera
 
     let cam = Camera::new();
@@ -78,19 +106,26 @@ fn main() {
 fn ray_color(r: Ray, world: &dyn Hittable, depth: u32, srng: &mut SmallRng, distrib: Uniform<f32> ) -> Vec3 {
     // recursion depth guard
     if depth == 0 {
-        return Vec3::new(0.0, 0.0, 0.0);
+        return Vec3::zero();
     }
 
     if let Some(rec) = world.hit(r, 0.001, f32::INFINITY){
-        let target = rec.p + rec.normal + Vec3::rand_unit_vector(srng, distrib);
-        return ray_color(
-            Ray{
-                orig: rec.p,
-                dir: target - rec.p,
+        let mut scattered = Ray {
+            orig: Vec3::zero(),
+            dir: Vec3::zero()
+        };
+        let mut attenuation = Vec3::zero();
+        match rec.material {
+            Some(mat) => {
+                if mat.scatter(r, rec, &mut attenuation, &mut scattered, srng, distrib) {
+                    return attenuation * ray_color(scattered, world, depth-1, srng, distrib);
+                };
+
             },
-            world, depth, srng, distrib
-        ) * 0.5;
+            None => return Vec3::zero(),
+        }
     }
+
     let unitdir = Vec3::as_unit(&r.dir);
     let t = 0.5 * (unitdir.y + 1.0);
     return Vec3::ones() * (1.0 - t) + Vec3::new(0.5, 0.7, 1.0) * t

src/material.rs

@@ -3,9 +3,62 @@ use crate::ray::Ray;
 use crate::hittable::HitRecord;
 use crate::Vec3;
 
-pub trait Material {
-    fn scatter(
-        &self, ray_in: Ray, rec: HitRecord, attenuation: Vec3, scattered: Ray
-    ) -> bool;
+use rand::Rng;
+use rand::rngs::SmallRng;
+use rand::distributions::Uniform;
+
+
+
+#[derive(Copy, Clone, Debug)]
+pub enum Material{
+    Lambertian{ albedo: Vec3 },
+    Metal{ albedo:Vec3 },
 }
 
+impl Material {
+    pub fn scatter(
+        &self,
+        ray_in: Ray,
+        rec: HitRecord,
+        attenuation: &mut Vec3,
+        scattered:&mut Ray,
+        srng: &mut SmallRng,
+        distrib: Uniform<f32>,
+    ) -> bool {
+        match self {
+            Material::Lambertian { albedo } => {
+                let scatter_dir = rec.normal + Vec3::rand_unit_vector(srng, distrib);
+                // The compiler might be smart enough to compute this ^^^ just once. In which case,
+                // I don't need to do this weird dance. Oh well. It'll work.
+                let scatter_dir = if scatter_dir.near_zero() {  // if near zero,
+                    rec.normal                                  // replace with normal
+                } else {
+                    scatter_dir                                 // else preserve current
+                };
+
+                //TODO: Revisit this out-parameter pattern
+                // It's a side effect of C++'s obtuse move semantics (and the RTIOW author not
+                // using them at all)
+                *scattered = Ray{
+                    orig: rec.p,
+                    dir: scatter_dir
+                };
+                *attenuation = *albedo; // deref on both sides? Wacky
+                return true;
+            },
+            Material::Metal { albedo } => {
+                let reflected = Vec3::reflect(
+                    Vec3::as_unit(&ray_in.dir),
+                    rec.normal
+                );
+                *scattered = Ray{
+                    orig: rec.p,
+                    dir: reflected,
+                };
+                *attenuation = *albedo;
+                return Vec3::dot(scattered.dir, rec.normal) > 0.0;
+            },
+            _ => return false,
+        }
+    }
+}

src/sphere.rs

@@ -7,12 +7,10 @@ use crate::hittable::{
 use crate::material::Material;
 use crate::ray::Ray;
 
-use std::rc::Rc;
-
 pub struct Sphere{
     pub center: Vec3,
     pub radius: f32,
-    pub material: Option<Rc<dyn Material>>,
+    pub material: Option<Material>,
 }
 
 impl Hittable for Sphere {
@@ -39,7 +37,7 @@ impl Hittable for Sphere {
         let mut record = HitRecord{
             p: r.at(root),
             normal: (r.at(root) - self.center) / self.radius,
-            material: self.material.clone(),
+            material: self.material,
             t: root,
             front_face: false,
         };

src/vec3.rs

@@ -92,6 +92,18 @@ impl Vec3{
         let ib = (Vec3::clamp(b, 0.0, 0.999) * 256.0) as i32;
         format!("{} {} {}", ir, ig, ib)
     }
+    
+    pub fn near_zero(&self) -> bool {
+        let epsilon: f32 = 1e-8;
+        return 
+            self.x < epsilon &&
+            self.y < epsilon &&
+            self.z < epsilon
+    }
+    
+    pub fn reflect(v: Vec3, n: Vec3) -> Vec3 {
+        return v - n * Vec3::dot(v, n) * 2.0;
+    }
 
     pub fn dot(left: Vec3, right: Vec3) -> f32{
         left.x * right.x +