bevy_math/sampling/
mesh_sampling.rs

1//! Functionality related to random sampling from triangle meshes.
2
3use crate::{
4    primitives::{Measured2d, Triangle3d},
5    ShapeSample, Vec3,
6};
7use alloc::vec::Vec;
8use rand::Rng;
9use rand_distr::{
10    weighted::{Error as WeightedError, WeightedAliasIndex},
11    Distribution,
12};
13
14/// A [distribution] that caches data to allow fast sampling from a collection of triangles.
15/// Generally used through [`sample`] or [`sample_iter`].
16///
17/// [distribution]: Distribution
18/// [`sample`]: Distribution::sample
19/// [`sample_iter`]: Distribution::sample_iter
20///
21/// Example
22/// ```
23/// # use bevy_math::{Vec3, primitives::*};
24/// # use bevy_math::sampling::mesh_sampling::UniformMeshSampler;
25/// # use rand::{SeedableRng, rngs::StdRng, distr::Distribution};
26/// let faces = Tetrahedron::default().faces();
27/// let sampler = UniformMeshSampler::try_new(faces).unwrap();
28/// let rng = StdRng::seed_from_u64(8765309);
29/// // 50 random points on the tetrahedron:
30/// let samples: Vec<Vec3> = sampler.sample_iter(rng).take(50).collect();
31/// ```
32pub struct UniformMeshSampler {
33    triangles: Vec<Triangle3d>,
34    face_distribution: WeightedAliasIndex<f32>,
35}
36
37impl Distribution<Vec3> for UniformMeshSampler {
38    fn sample<R: Rng + ?Sized>(&self, rng: &mut R) -> Vec3 {
39        let face_index = self.face_distribution.sample(rng);
40        self.triangles[face_index].sample_interior(rng)
41    }
42}
43
44impl UniformMeshSampler {
45    /// Construct a new [`UniformMeshSampler`] from a list of [triangles].
46    ///
47    /// Returns an error if the distribution of areas for the collection of triangles could not be formed
48    /// (most notably if the collection has zero surface area).
49    ///
50    /// [triangles]: Triangle3d
51    pub fn try_new<T: IntoIterator<Item = Triangle3d>>(
52        triangles: T,
53    ) -> Result<Self, WeightedError> {
54        let triangles: Vec<Triangle3d> = triangles.into_iter().collect();
55        let areas = triangles.iter().map(Measured2d::area).collect();
56
57        WeightedAliasIndex::new(areas).map(|face_distribution| Self {
58            triangles,
59            face_distribution,
60        })
61    }
62}
bevy_math/sampling/mesh_sampling.rs

bevy_math/sampling/
mesh_sampling.rs
