From 7b0c09c3d7fd46f969c9fac2fbdb6941de6ced66 Mon Sep 17 00:00:00 2001
From: numzero <numzer0@yandex.ru>
Date: Sat, 16 Nov 2024 23:52:18 +0300
Subject: [PATCH] Add custom cylinder

---
 src/shape/cylinder.rs | 78 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 78 insertions(+)

diff --git a/src/shape/cylinder.rs b/src/shape/cylinder.rs
index baf21a9..0f06a21 100644
--- a/src/shape/cylinder.rs
+++ b/src/shape/cylinder.rs
@@ -2,6 +2,67 @@ use glam::{Vec3, Vec3Swizzles as _};
 
 use crate::types::Ray;
 
+pub struct Cylinder {
+	pub center: Vec3,
+	pub semiaxis: Vec3,
+	pub radius: f32,
+}
+
+impl Cylinder {
+	/// Split a vector into a component along the axis and one orthogonal to it.
+	fn split(&self, dir: Vec3) -> (f32, Vec3) {
+		let along = dir.dot(self.semiaxis) / self.semiaxis.length_squared();
+		(along, dir - along * self.semiaxis)
+	}
+
+	fn cap_inout(p: f32, d: f32) -> (f32, f32) {
+		((-d.signum() - p) / d.abs(), (d.signum() - p) / d.abs())
+	}
+
+	pub fn is_inside(&self, pt: Vec3) -> bool {
+		let (along, ortho) = self.split(pt - self.center);
+		along.abs() < 1. && ortho.length_squared() < self.radius.powi(2)
+	}
+
+	fn trace_inout(&self, ray: Ray) -> Option<(f32, f32)> {
+		let (pos_along, pos_ortho) = self.split(ray.pos - self.center);
+		let (dir_along, dir_ortho) = self.split(ray.dir);
+		let (t_cap_in, t_cap_out) = Self::cap_inout(pos_along, dir_along);
+		if dir_ortho.length_squared() < 1e-3 {
+			if pos_ortho.length_squared() >= self.radius.powi(2) {
+				return None;
+			}
+			return Some((t_cap_in, t_cap_out));
+		}
+		let (t_side_in, t_side_out) = solve_quadratic(
+			dir_ortho.length_squared(),
+			pos_ortho.dot(dir_ortho),
+			pos_ortho.length_squared() - self.radius.powi(2),
+		)?;
+		let t_in = f32::max(t_cap_in, t_side_in);
+		let t_out = f32::min(t_cap_out, t_side_out);
+		if t_out <= t_in {
+			return None;
+		}
+		Some((t_in, t_out))
+	}
+
+	pub fn trace_into(&self, ray: Ray) -> Option<f32> {
+		let (t, _) = self.trace_inout(ray)?;
+		if t < 0. {
+			return None;
+		}
+		Some(t)
+	}
+
+	pub fn trace_out_of(&self, ray: Ray) -> Option<f32> {
+		let (_, t) = self
+			.trace_inout(ray)
+			.expect("the ray starts inside so *has* to cross the boundary");
+		Some(t)
+	}
+}
+
 /// Цилиндр с центром в начале координат и осью вдоль оси Y.
 pub struct YCylinder {
 	pub half_length: f32,
@@ -88,6 +149,23 @@ mod tests {
 	use crate::types::ray;
 	use approx::assert_abs_diff_eq;
 	use glam::vec3;
+	use rand::{Rng, SeedableRng};
+
+	#[test]
+	fn test_split() {
+		let mut rng = rand_pcg::Pcg64Mcg::seed_from_u64(17);
+		let cyl = Cylinder {
+			center: vec3(1., 2., 3.),
+			semiaxis: vec3(4., 5., 6.),
+			radius: 7.,
+		};
+		for _ in 0..100 {
+			let dir = vec3(rng.gen(), rng.gen(), rng.gen());
+			let (along, ortho) = cyl.split(dir);
+			assert_abs_diff_eq!(along * cyl.semiaxis + ortho, dir, epsilon = 1e-5);
+			assert_abs_diff_eq!(cyl.semiaxis.dot(ortho), 0., epsilon = 1e-5);
+		}
+	}
 
 	#[test]
 	fn test_cylinder() {