diff --git a/src/bin/mesh/main.rs b/src/bin/mesh/main.rs
index db0281e..b8c27fe 100644
--- a/src/bin/mesh/main.rs
+++ b/src/bin/mesh/main.rs
@@ -88,6 +88,27 @@ fn render(mesh: &Mesh, camera: impl Fn(Vec2) -> (Vec3, Vec3)) -> Image {
 	img
 }
 
+fn persp(dist: f32, off: Vec2) -> (Vec3, Vec3) {
+	(vec3(0., 0., -dist), vec3(off.x, off.y, dist))
+}
+
+fn ortho(dist: f32, off: Vec2) -> (Vec3, Vec3) {
+	(vec3(off.x, off.y, -dist), vec3(0., 0., 1.))
+}
+
+#[test]
+fn test_projs() {
+	fn check(f: fn(dist: f32, off: Vec2) -> (Vec3, Vec3), x: f32, y: f32, z: f32) {
+		let (base, ray) = f(z, vec2(x, y));
+		let at_dist = base + ray * (z / ray.z);
+		assert_eq!(at_dist, vec3(x, y, 0.));
+	}
+	check(persp, 1., 2., 3.);
+	check(ortho, 1., 2., 3.);
+	check(persp, 5., 3., 7.);
+	check(ortho, 9., 1., 8.);
+}
+
 #[show_image::main]
 fn main() -> Result<(), Box<dyn Error>> {
 	let args: Vec<String> = env::args().collect();
@@ -100,6 +121,7 @@ fn main() -> Result<(), Box<dyn Error>> {
 		let mut f = BufReader::new(f);
 		load_mesh(&mut f)?
 	};
+	let proj = persp;
 	let window = show_image::create_window("Raytracing", WindowOptions::default())?;
 	loop {
 		for phi in 0..360 {
@@ -110,14 +132,7 @@ fn main() -> Result<(), Box<dyn Error>> {
 			));
 			let m_camera = m_view.transpose();
 			let img = render(mesh.as_slice(), |off| {
-				// perspective projection
-				let base = vec3(0.0, 0.0, -40.0);
-				let ray = vec3(off.x, off.y, 2.0);
-
-				// orthographic projection
-				// let base = vec3(off.x, off.y, -10.0);
-				// let ray = vec3(0.0, 0.0, 1.0);
-
+				let (base, ray) = proj(40., 20. * off);
 				(m_camera * base, m_camera * ray)
 			});