From 4fad56a7d1f36e1227bda7589502790c9a29a33f Mon Sep 17 00:00:00 2001
From: numzero <numzer0@yandex.ru>
Date: Sat, 17 Oct 2026 22:55:45 +0300
Subject: [PATCH] fix normals for the gear teeth

---
 src/crown_gear.rs | 110 +++++++++++++++++++++++++++++++++++-----------
 1 file changed, 85 insertions(+), 25 deletions(-)

diff --git a/src/crown_gear.rs b/src/crown_gear.rs
index 0ee3be1..d3e1b6b 100644
--- a/src/crown_gear.rs
+++ b/src/crown_gear.rs
@@ -23,7 +23,7 @@ impl CrownGear {
 		let outer_scale = self.outer_radius / self.pitch_radius;
 
 		let mut mesh = CpuMeshIndexed::new();
-		mesh.vertices.reserve_exact(4 * sides);
+		mesh.vertices.reserve_exact(8 * sides);
 		mesh.faces.reserve_exact(8 * sides);
 		for k in 0..sides {
 			let t = k as f32 / sides as f32;
@@ -31,24 +31,22 @@ impl CrownGear {
 			let (s, c) = phi.sin_cos();
 			let tooth = t * teeth;
 			let y = self.profile.y_from_tooth(tooth);
-			mesh.vertices.push(Vertex {
-				position: vec3(
-					c * self.inner_radius,
-					s * self.inner_radius,
-					-self.base_thickness,
-				),
-				color,
-				normal: Vec3::ZERO, // FIXME calculate the normal
-			});
-			mesh.vertices.push(Vertex {
-				position: vec3(
-					c * self.outer_radius,
-					s * self.outer_radius,
-					-self.base_thickness,
-				),
-				color,
-				normal: Vec3::ZERO, // FIXME calculate the normal
-			});
+			let eps = 1e-3;
+			let dy_dt = teeth
+				* (self.profile.y_from_tooth(tooth + eps) - self.profile.y_from_tooth(tooth - eps))
+				/ (2.0 * eps);
+
+			let v_radial = vec3(c * self.pitch_radius, s * self.pitch_radius, y);
+			let v_tan = vec3(-2.0 * PI * s, 2.0 * PI * c, dy_dt / self.pitch_radius);
+			let n_top = v_radial.cross(v_tan).normalize();
+
+			let n_top = vec3(
+				s * dy_dt - 2.0 * PI * c * y,
+				-c * dy_dt - 2.0 * PI * s * y,
+				2.0 * PI * self.pitch_radius,
+			);
+
+			// top
 			mesh.vertices.push(Vertex {
 				position: vec3(
 					c * self.outer_radius,
@@ -56,7 +54,7 @@ impl CrownGear {
 					outer_scale * y,
 				),
 				color,
-				normal: Vec3::ZERO, // FIXME calculate the normal
+				normal: n_top,
 			});
 			mesh.vertices.push(Vertex {
 				position: vec3(
@@ -65,12 +63,74 @@ impl CrownGear {
 					inner_scale * y,
 				),
 				color,
-				normal: Vec3::ZERO, // FIXME calculate the normal
+				normal: n_top,
 			});
-			let base1 = 4 * k;
-			let base2 = 4 * ((k + 1) % sides);
-			for j1 in 0..4 {
-				let j2 = (j1 + 1) % 4;
+
+			// bottom
+			mesh.vertices.push(Vertex {
+				position: vec3(
+					c * self.inner_radius,
+					s * self.inner_radius,
+					-self.base_thickness,
+				),
+				color,
+				normal: vec3(0.0, 0.0, -1.0),
+			});
+			mesh.vertices.push(Vertex {
+				position: vec3(
+					c * self.outer_radius,
+					s * self.outer_radius,
+					-self.base_thickness,
+				),
+				color,
+				normal: vec3(0.0, 0.0, -1.0),
+			});
+
+			// inner
+			mesh.vertices.push(Vertex {
+				position: vec3(
+					c * self.inner_radius,
+					s * self.inner_radius,
+					inner_scale * y,
+				),
+				color,
+				normal: vec3(-c, -s, 0.0),
+			});
+			mesh.vertices.push(Vertex {
+				position: vec3(
+					c * self.inner_radius,
+					s * self.inner_radius,
+					-self.base_thickness,
+				),
+				color,
+				normal: vec3(-c, -s, 0.0),
+			});
+
+			// outer
+			mesh.vertices.push(Vertex {
+				position: vec3(
+					c * self.outer_radius,
+					s * self.outer_radius,
+					-self.base_thickness,
+				),
+				color,
+				normal: vec3(c, s, 0.0),
+			});
+			mesh.vertices.push(Vertex {
+				position: vec3(
+					c * self.outer_radius,
+					s * self.outer_radius,
+					outer_scale * y,
+				),
+				color,
+				normal: vec3(c, s, 0.0),
+			});
+
+			let base1 = 8 * k;
+			let base2 = 8 * ((k + 1) % sides);
+			for j in 0..4 {
+				let j1 = 2 * j;
+				let j2 = 2 * j + 1;
 				mesh.faces.push(
 					[base1 + j1, base2 + j1, base1 + j2].map(|index| index.try_into().unwrap()),
 				);