zigrtiow: dielectric w/o internal reflection.

zigrtiow/src/main.zig

@@ -16,6 +16,7 @@ const Hittable = hittable.Hittable;
 const HittableList = hittable_list.HittableList;
 const Labertian = material.Labertian;
 const Metal = material.Metal;
+const Dielectric = material.Dielectric;
 const Material = material.Material;
 const Point3 = vec.Point3;
 const Ray = ray.Ray;
@@ -89,8 +90,10 @@ pub fn main() anyerror!void {
     var tmp_world = HittableList.init();
 
     const material_ground = Material{ .labertian = Labertian{ .albedo = Color.init(0.8, 0.8, 0.0) } };
-    const material_center = Material{ .labertian = Labertian{ .albedo = Color.init(0.7, 0.3, 0.3) } };
-    const material_left = Material{ .metal = Metal{ .albedo = Color.init(0.8, 0.8, 0.8), .fuzz = 0.3 } };
+    const material_center = Material{ .dielectric = Dielectric{ .ir = 1.5 } };
+    //const material_center = Material{ .labertian = Labertian{ .albedo = Color.init(0.7, 0.3, 0.3) } };
+    const material_left = Material{ .dielectric = Dielectric{ .ir = 1.5 } };
+    //const material_left = Material{ .metal = Metal{ .albedo = Color.init(0.8, 0.8, 0.8), .fuzz = 0.3 } };
     const material_right = Material{ .metal = Metal{ .albedo = Color.init(0.8, 0.6, 0.2), .fuzz = 1.0 } };
 
     try tmp_world.add(Hittable{ .sphere = Sphere.init(Point3.init(0, -100.5, -1), 100, material_ground) });

zigrtiow/src/material.zig

@@ -10,11 +10,13 @@ const random_in_unit_sphere = vec.random_in_unit_sphere;
 pub const Material = union(enum) {
     labertian: Labertian,
     metal: Metal,
+    dielectric: Dielectric,
 
     pub fn scatter(material: Material, r_in: Ray, rec: HitRecord) ?ScatterRec {
         return switch (material) {
             .labertian => |labertian| labertian.scatter(r_in, rec),
             .metal => |metal| metal.scatter(r_in, rec),
+            .dielectric => |dielectric| dielectric.scatter(r_in, rec),
         };
     }
 };
@@ -57,3 +59,27 @@ pub const Metal = struct {
         return v.sub(n.scale(v.dot(n) * 2));
     }
 };
+
+pub const Dielectric = struct {
+    ir: f32, // Index of Refraction
+
+    pub fn scatter(dielectric: Dielectric, r_in: Ray, rec: HitRecord) ?ScatterRec {
+        const attenuation = Color.init(1, 1, 1);
+        const refraction_ratio = if (rec.front_face) 1.0 / dielectric.ir else dielectric.ir;
+
+        const unit_direction = r_in.direction().unit();
+        const refracted = refract(unit_direction, rec.normal, refraction_ratio);
+
+        const scattered = Ray.init(rec.p, refracted);
+        return ScatterRec{
+            .attenuation = attenuation,
+            .scattered = scattered,
+        };
+    }
+    fn refract(uv: Vec3, n: Vec3, etai_over_etat: f32) Vec3 {
+        const cos_theta = @minimum(-uv.dot(n), 1.0);
+        const r_out_perp = uv.add(n.scale(cos_theta)).scale(etai_over_etat);
+        const r_out_parallel = n.scale(-@sqrt(@fabs(1.0 - r_out_perp.length_squared())));
+        return r_out_perp.add(r_out_parallel);
+    }
+};