From 77cab94a6e50e8247c4e1a9c050facfeaadbb59c Mon Sep 17 00:00:00 2001
From: numzero <numzer0@yandex.ru>
Date: Mon, 24 Nov 2025 17:10:12 +0300
Subject: [PATCH] add basic shape generation

---
 src/lib.rs   |   1 +
 src/shape.rs | 140 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 141 insertions(+)
 create mode 100644 src/shape.rs

diff --git a/src/lib.rs b/src/lib.rs
index 18937dd..ce55aa2 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -15,6 +15,7 @@ use crate::{
 mod camera;
 mod ray;
 mod render;
+mod shape;
 mod trace;
 
 const OUTPUT_FORMAT: wgpu::TextureFormat = wgpu::TextureFormat::Bgra8UnormSrgb;
diff --git a/src/shape.rs b/src/shape.rs
new file mode 100644
index 0000000..e1b5865
--- /dev/null
+++ b/src/shape.rs
@@ -0,0 +1,140 @@
+use std::f32::consts::PI;
+
+use glam::{Vec3, vec3};
+
+pub type Face = [u16; 3];
+
+#[derive(Debug, Clone)]
+pub struct Mesh {
+	pub vertices: Vec<Vec3>,
+	pub indices: Vec<Face>,
+}
+
+pub fn sphere(subdiv: usize) -> Mesh {
+	assert!(subdiv >= 2);
+	assert!(2 * subdiv * (subdiv - 1) + 2 <= 1 << 16);
+
+	let mut vertices = Vec::new();
+	vertices.push(Vec3::Z);
+	for j in 1..subdiv {
+		let v = j as f32 / subdiv as f32;
+		let theta = PI * v;
+		let (xy, z) = theta.sin_cos();
+		for i in 0..2 * subdiv {
+			let u = i as f32 / (2 * subdiv) as f32;
+			let phi = 2. * PI * u;
+			let (y, x) = phi.sin_cos();
+			vertices.push(vec3(xy * x, xy * y, z));
+		}
+	}
+	vertices.push(-Vec3::Z);
+	assert_eq!(vertices.len(), 2 * subdiv * (subdiv - 1) + 2);
+
+	let mut indices = Vec::new();
+	let subdiv = subdiv as u16;
+	for i in 0..2 * subdiv - 1 {
+		indices.push([0, i + 1, i + 2]);
+	}
+	indices.push([0, 2 * subdiv, 1]);
+	for j in 0..subdiv - 2 {
+		let k1 = j * 2 * subdiv + 1;
+		let k2 = k1 + 2 * subdiv;
+		for i in 0..2 * subdiv - 1 {
+			let a = k1 + i;
+			let b = k2 + i;
+			indices.push([a, b, b + 1]);
+			indices.push([a, b + 1, a + 1]);
+		}
+		let a = k1 + 2 * subdiv - 1;
+		let b = k2 + 2 * subdiv - 1;
+		indices.push([a, b, k2]);
+		indices.push([a, k2, k1]);
+	}
+	let k1 = 2 * subdiv * (subdiv - 2) + 1;
+	let k2 = 2 * subdiv * (subdiv - 1) + 1;
+	for i in 0..2 * subdiv - 1 {
+		indices.push([k1 + i, k2, k1 + i + 1]);
+	}
+	indices.push([k1 + 2 * subdiv - 1, k2, k1]);
+
+	Mesh { vertices, indices }
+}
+
+#[cfg(test)]
+mod tests {
+	use approx::abs_diff_eq;
+
+	use super::*;
+
+	#[test]
+	fn test_sphere_2_topology() {
+		assert_eq!(
+			sphere(2).indices,
+			vec![
+				[0, 1, 2],
+				[0, 2, 3],
+				[0, 3, 4],
+				[0, 4, 1],
+				[1, 5, 2],
+				[2, 5, 3],
+				[3, 5, 4],
+				[4, 5, 1],
+			]
+		);
+	}
+
+	fn are_equal_eps(left: &[Vec3], right: &[Vec3], eps: f32) -> bool {
+		if left.len() != right.len() {
+			return false;
+		}
+		left.iter()
+			.zip(right.iter())
+			.all(|(a, b)| abs_diff_eq!(a, b, epsilon = eps))
+	}
+
+	#[test]
+	fn test_sphere_2_geometry() {
+		let left = sphere(2).vertices;
+		let right = [Vec3::Z, Vec3::X, Vec3::Y, -Vec3::X, -Vec3::Y, -Vec3::Z];
+		assert!(
+			are_equal_eps(&left, &right, 1e-6),
+			"assertion `left == right` failed\n  left: {left:?}\n right: {right:?}"
+		);
+	}
+
+	#[test]
+	fn test_sphere_3_topology() {
+		assert_eq!(
+			sphere(3).indices,
+			vec![
+				// top
+				[0, 1, 2],
+				[0, 2, 3],
+				[0, 3, 4],
+				[0, 4, 5],
+				[0, 5, 6],
+				[0, 6, 1],
+				// belt
+				[1, 7, 8],
+				[1, 8, 2],
+				[2, 8, 9],
+				[2, 9, 3],
+				[3, 9, 10],
+				[3, 10, 4],
+				[4, 10, 11],
+				[4, 11, 5],
+				[5, 11, 12],
+				[5, 12, 6],
+				[6, 12, 7],
+				[6, 7, 1],
+				// bottom
+				[7, 13, 8],
+				[8, 13, 9],
+				[9, 13, 10],
+				[10, 13, 11],
+				[11, 13, 12],
+				[12, 13, 7],
+			]
+		);
+	}
+}