diff --git a/src/main.rs b/src/main.rs
index da50183..4491e80 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -2,7 +2,7 @@
 
 use std::{convert::identity, error::Error, f32::consts::PI, sync::Arc};
 
-use glam::{Mat4, vec3};
+use glam::{Mat4, Vec3, vec3};
 use winit::{
 	application::ApplicationHandler,
 	event::WindowEvent,
@@ -13,7 +13,7 @@ use winit::{
 use crate::{
 	camera::OrbitalCamera,
 	render::lines::{LookParams, Mesh, Pipeline, Vertex},
-	trace::Source,
+	trace::{Scene, Source, Sphere},
 };
 
 mod camera;
@@ -155,20 +155,54 @@ impl MainWindow {
 		self.pipeline
 			.render(&mut pass, [&Mesh::new(&self.device, &contour)]);
 
+		const BASE_R: f32 = 2.;
+		const BASE_POS: Vec3 = vec3(0., 0., -BASE_R);
+		const BASE: Sphere = Sphere {
+			position: vec3(0., 0., -BASE_R),
+			radius: BASE_R,
+		};
+		fn sphere(pos: Vec3) -> Sphere {
+			Sphere {
+				position: pos,
+				radius: BASE_POS.distance(pos) - BASE_R,
+			}
+		}
+		let scene = Scene {
+			objects: vec![
+				BASE,
+				sphere(vec3(0., 0., 0.1)),
+				sphere(vec3(0.3, 0., 0.1)),
+				sphere(vec3(0.1, 0.3, 0.1)),
+			],
+		};
+
 		let mut prng = rand_pcg::Pcg64::new(42, 0);
-		let rays: Vec<Vertex> = (0..1000)
+		let rays: Vec<Vertex> = (0..10000)
 			.flat_map(|_| {
 				let ray = source.make_ray(&mut prng);
-				[
-					Vertex {
-						pos: ray.base,
-						color: vec3(0., 0., 0.),
-					},
-					Vertex {
-						pos: ray.base + 0.1 * ray.dir,
-						color: vec3(1., 1., 1.),
-					},
-				]
+				if let Some(ray) = scene.trace_ray(ray) {
+					[
+						Vertex {
+							pos: ray.base - 0.02 * ray.dir,
+							color: vec3(1., 1., 1.),
+						},
+						Vertex {
+							pos: ray.base,
+							color: vec3(0., 1., 0.),
+						},
+					]
+				} else {
+					[
+						Vertex {
+							pos: ray.base,
+							color: vec3(1., 1., 1.),
+						},
+						Vertex {
+							pos: ray.base + 0.1 * ray.dir,
+							color: vec3(1., 0., 0.),
+						},
+					]
+				}
 			})
 			.collect();
 		self.pipeline
diff --git a/src/ray.rs b/src/ray.rs
index 265dd96..2617a75 100644
--- a/src/ray.rs
+++ b/src/ray.rs
@@ -1,6 +1,27 @@
 use glam::Vec3;
 
+#[derive(Debug, Clone, Copy)]
 pub struct Ray {
 	pub base: Vec3,
 	pub dir: Vec3,
 }
+
+impl Ray {
+	pub fn new(base: Vec3, dir: Vec3) -> Self {
+		Ray { base, dir }
+	}
+
+	pub fn normalize(self) -> Self {
+		Self {
+			base: self.base,
+			dir: self.dir.normalize(),
+		}
+	}
+
+	pub fn advance(self, amount: f32) -> Self {
+		Self {
+			base: self.base + amount * self.dir,
+			dir: self.dir,
+		}
+	}
+}
diff --git a/src/trace.rs b/src/trace.rs
index 196dc67..b1945c2 100644
--- a/src/trace.rs
+++ b/src/trace.rs
@@ -71,3 +71,45 @@ impl Source {
 		}
 	}
 }
+
+#[derive(Debug, Clone)]
+pub struct Sphere {
+	pub position: Vec3,
+	pub radius: f32,
+}
+
+impl Sphere {
+	fn trace_ray(&self, ray: Ray) -> Option<f32> {
+		// let t: f32;
+		// let hit = ray.base + t * ray.dir;
+		// (hit - self.position).length() == self.radius;
+		let Ray { base, dir } = ray;
+		let rel = base - self.position;
+		// (rel + t⋅dir)² == r²
+		// rel² − r² + 2⋅t⋅rel⋅dir + t²⋅dir² = 0
+		let a = dir.length_squared();
+		let b2 = rel.dot(dir);
+		let c = rel.length_squared() - self.radius.powi(2);
+		let d4 = b2.powi(2) - a * c;
+		if d4 < 0. {
+			return None;
+		}
+		Some((-b2 - d4.sqrt()) / a)
+	}
+}
+
+#[derive(Debug)]
+pub struct Scene {
+	pub objects: Vec<Sphere>,
+}
+
+impl Scene {
+	pub fn trace_ray(&self, ray: Ray) -> Option<Ray> {
+		let dist = self
+			.objects
+			.iter()
+			.filter_map(|obj| obj.trace_ray(ray))
+			.min_by(f32::total_cmp);
+		Some(ray.advance(dist?))
+	}
+}