create some rays

src/main.rs

@@ -17,6 +17,7 @@ use crate::{
 };
 
 mod camera;
+mod ray;
 mod render;
 mod trace;
 
@@ -141,8 +142,10 @@ impl MainWindow {
 			position_yaw: 0.0,
 			position_pitch: PI / 3.,
 			distance: 1.0,
-			diameter: 0.25,
+			radius: 0.125,
+			spread: 0.125,
 		};
+
 		let contour: Vec<Vertex> = loop_list(source.contour(17))
 			.map(|pos| Vertex {
 				pos,
@@ -152,6 +155,25 @@ impl MainWindow {
 		self.pipeline
 			.render(&mut pass, [&Mesh::new(&self.device, &contour)]);
 
+		let mut prng = rand_pcg::Pcg64::new(42, 0);
+		let rays: Vec<Vertex> = (0..1000)
+			.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.),
+					},
+				]
+			})
+			.collect();
+		self.pipeline
+			.render(&mut pass, [&Mesh::new(&self.device, &rays)]);
+
 		drop(pass);
 		self.queue.submit(std::iter::once(encoder.finish()));
 	}

src/ray.rs

@@ -0,0 +1,6 @@
+use glam::Vec3;
+
+pub struct Ray {
+	pub base: Vec3,
+	pub dir: Vec3,
+}

src/trace.rs

@@ -1,8 +1,9 @@
 use std::f32::consts::PI;
 
-use glam::{Mat4, Vec3, vec3};
+use glam::{Mat4, Vec2, Vec3, vec3};
+use rand_distr::Distribution;
 
-use crate::camera::OrbitalCamera;
+use crate::{camera::OrbitalCamera, ray::Ray};
 
 #[derive(Debug, Clone)]
 pub struct Source {
@@ -16,7 +17,9 @@ pub struct Source {
 	pub distance: f32,
 
 	/// Disc diameter.
-	pub diameter: f32,
+	pub radius: f32,
+
+	pub spread: f32,
 }
 
 impl Source {
@@ -44,12 +47,27 @@ impl Source {
 
 	pub fn contour(&self, n: usize) -> impl Iterator<Item = Vec3> {
 		let step = 2. * PI / n as f32;
-		let r = 0.5 * self.diameter;
 		let m = self.transform();
 		(0..n).map(move |k| {
 			let angle = (k as f32) * step;
 			let (x, y) = angle.sin_cos();
-			m.transform_point3(r * vec3(x, y, 0.))
+			m.transform_point3(self.radius * vec3(x, y, 0.))
 		})
 	}
+
+	pub fn make_ray(&self, rng: &mut impl rand::Rng) -> Ray {
+		let base: Vec2 = rand_distr::UnitDisc.sample(rng).into();
+		let off: f32 = rand_distr::StandardUniform.sample(rng);
+		let side: Vec2 = rand_distr::UnitCircle.sample(rng).into();
+
+		let m = self.transform();
+		let base = Vec3::from((self.radius * base, 0.));
+		let fwd = 1. - self.spread * off;
+		let side_scale = (1. - fwd.powi(2)).sqrt();
+		let dir = Vec3::from((side_scale * side, fwd));
+		Ray {
+			base: m.transform_point3(base),
+			dir: m.transform_vector3(dir),
+		}
+	}
 }