Add fuzz parameter to reflective material

src/material.c

@@ -34,10 +34,15 @@ bool scatter_reflective(
     material_params_t params, hit_t hit, rng_t *rng, ray_t *ray,
     vec3_t *atten_out)
 {
-	(void)rng;
+	vec3_t reflected = reflect(ray->dir, hit.normal);
+	if (params.reflective.fuzz != 0.0) {
+		const double weight = params.reflective.fuzz * rng_canon(rng);
+		const vec3_t scatter = vec3_scale(rng_vec3(rng), weight);
+		reflected = vec3_unit(vec3_add(reflected, scatter));
+	}
 
 	ray->orig = hit.point;
-	ray->dir = reflect(ray->dir, hit.normal);
+	ray->dir = reflected;
 	*atten_out = params.reflective.tint;
 	return true;
 }