From 713fd25c9c88f03e576fb9a54bf7473bd56c0677 Mon Sep 17 00:00:00 2001
From: numzero <numzer0@yandex.ru>
Date: Thu, 20 Nov 2025 13:05:02 +0300
Subject: [PATCH] add generic reflector

---
 src/trace.rs | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/src/trace.rs b/src/trace.rs
index 5f461e6..baa2633 100644
--- a/src/trace.rs
+++ b/src/trace.rs
@@ -1,7 +1,7 @@
 use std::f32::consts::PI;
 
 use glam::{Mat4, Vec2, Vec3, vec3};
-use rand_distr::Distribution;
+use rand_distr::{Distribution, UnitSphere};
 
 use crate::{camera::OrbitalCamera, ray::Ray};
 
@@ -134,3 +134,27 @@ impl Scene {
 		})
 	}
 }
+
+pub trait Reflector {
+	fn brdf(&self, normal: Vec3, incident: Vec3, reflected: Vec3) -> f32 /* 1/sr */;
+	fn reflect(&self, rgen: &mut impl rand::Rng, normal: Vec3, incident: Vec3) -> Vec3;
+}
+
+pub struct Lambertian;
+
+impl Reflector for Lambertian {
+	fn brdf(&self, _normal: Vec3, _incident: Vec3, _reflected: Vec3) -> f32 {
+		1. / PI
+	}
+
+	fn reflect(&self, rgen: &mut impl rand::Rng, normal: Vec3, _incident: Vec3) -> Vec3 {
+		let sphere: Vec3 = UnitSphere.sample(rgen).into();
+		let sphere_n = normal.dot(sphere); // uniform on [-1, 1]!
+		let sphere_t = sphere - sphere_n * normal;
+
+		let out_n_len2 = sphere_n.abs();
+		let out_t = (1. + out_n_len2).recip().sqrt() * sphere_t;
+		let out_n = out_n_len2.sqrt() * normal;
+		out_t + out_n
+	}
+}