bevy_mesh/primitives/dim3/
triangle3d.rs

1use crate::{Indices, Mesh, MeshBuilder, Meshable};
2use bevy_asset::RenderAssetUsages;
3use bevy_math::{primitives::Triangle3d, Vec3};
4use wgpu::PrimitiveTopology;
5
6/// A builder used for creating a [`Mesh`] with a [`Triangle3d`] shape.
7pub struct Triangle3dMeshBuilder {
8    triangle: Triangle3d,
9}
10
11impl MeshBuilder for Triangle3dMeshBuilder {
12    fn build(&self) -> Mesh {
13        let positions: Vec<_> = self.triangle.vertices.into();
14        let uvs: Vec<_> = uv_coords(&self.triangle).into();
15
16        // Every vertex has the normal of the face of the triangle (or zero if the triangle is degenerate).
17        let normal: Vec3 = normal_vec(&self.triangle);
18        let normals = vec![normal; 3];
19
20        let indices = Indices::U32(vec![0, 1, 2]);
21
22        Mesh::new(
23            PrimitiveTopology::TriangleList,
24            RenderAssetUsages::default(),
25        )
26        .with_inserted_indices(indices)
27        .with_inserted_attribute(Mesh::ATTRIBUTE_POSITION, positions)
28        .with_inserted_attribute(Mesh::ATTRIBUTE_NORMAL, normals)
29        .with_inserted_attribute(Mesh::ATTRIBUTE_UV_0, uvs)
30    }
31}
32
33impl Meshable for Triangle3d {
34    type Output = Triangle3dMeshBuilder;
35
36    fn mesh(&self) -> Self::Output {
37        Triangle3dMeshBuilder { triangle: *self }
38    }
39}
40
41/// The normal of a [`Triangle3d`] with zeroing so that a [`Vec3`] is always obtained for meshing.
42#[inline]
43pub(crate) fn normal_vec(triangle: &Triangle3d) -> Vec3 {
44    triangle.normal().map_or(Vec3::ZERO, Into::into)
45}
46
47/// Unskewed uv-coordinates for a [`Triangle3d`].
48#[inline]
49pub(crate) fn uv_coords(triangle: &Triangle3d) -> [[f32; 2]; 3] {
50    let [a, b, c] = triangle.vertices;
51
52    let main_length = a.distance(b);
53    let Some(x) = (b - a).try_normalize() else {
54        return [[0., 0.], [1., 0.], [0., 1.]];
55    };
56    let y = c - a;
57
58    // `x` corresponds to one of the axes in uv-coordinates;
59    // to uv-map the triangle without skewing, we use the orthogonalization
60    // of `y` with respect to `x` as the second direction and construct a rectangle that
61    // contains `triangle`.
62    let y_proj = y.project_onto_normalized(x);
63
64    // `offset` represents the x-coordinate of the point `c`; note that x has been shrunk by a
65    // factor of `main_length`, so `offset` follows it.
66    let offset = y_proj.dot(x) / main_length;
67
68    // Obtuse triangle leaning to the left => x direction extends to the left, shifting a from 0.
69    if offset < 0. {
70        let total_length = 1. - offset;
71        let a_uv = [offset.abs() / total_length, 0.];
72        let b_uv = [1., 0.];
73        let c_uv = [0., 1.];
74
75        [a_uv, b_uv, c_uv]
76    }
77    // Obtuse triangle leaning to the right => x direction extends to the right, shifting b from 1.
78    else if offset > 1. {
79        let a_uv = [0., 0.];
80        let b_uv = [1. / offset, 0.];
81        let c_uv = [1., 1.];
82
83        [a_uv, b_uv, c_uv]
84    }
85    // Acute triangle => no extending necessary; a remains at 0 and b remains at 1.
86    else {
87        let a_uv = [0., 0.];
88        let b_uv = [1., 0.];
89        let c_uv = [offset, 1.];
90
91        [a_uv, b_uv, c_uv]
92    }
93}
94
95impl From<Triangle3d> for Mesh {
96    fn from(triangle: Triangle3d) -> Self {
97        triangle.mesh().build()
98    }
99}
100
101#[cfg(test)]
102mod tests {
103    use super::uv_coords;
104    use bevy_math::primitives::Triangle3d;
105
106    #[test]
107    fn uv_test() {
108        use bevy_math::vec3;
109        let mut triangle = Triangle3d::new(vec3(0., 0., 0.), vec3(2., 0., 0.), vec3(-1., 1., 0.));
110
111        let [a_uv, b_uv, c_uv] = uv_coords(&triangle);
112        assert_eq!(a_uv, [1. / 3., 0.]);
113        assert_eq!(b_uv, [1., 0.]);
114        assert_eq!(c_uv, [0., 1.]);
115
116        triangle.vertices[2] = vec3(3., 1., 0.);
117        let [a_uv, b_uv, c_uv] = uv_coords(&triangle);
118        assert_eq!(a_uv, [0., 0.]);
119        assert_eq!(b_uv, [2. / 3., 0.]);
120        assert_eq!(c_uv, [1., 1.]);
121
122        triangle.vertices[2] = vec3(2., 1., 0.);
123        let [a_uv, b_uv, c_uv] = uv_coords(&triangle);
124        assert_eq!(a_uv, [0., 0.]);
125        assert_eq!(b_uv, [1., 0.]);
126        assert_eq!(c_uv, [1., 1.]);
127    }
128}
bevy_mesh/primitives/dim3/triangle3d.rs

bevy_mesh/primitives/dim3/
triangle3d.rs
