shape.rs

#[derive(Debug, Clone, Default)]
pub struct Shape {
    pub vertices: Vec<V3>,
    pub tris: Vec<[u16; 3]>,
}
impl Shape {
    // ...
    pub fn new_sphere(radius: f32, bands: (usize, usize)) -> Self {
        use std::{f32, u16};
        assert_le!(bands.0 * bands.1 * 4, u16::MAX as usize);
        let mut vertices = Vec::with_capacity(bands.0 * bands.1 * 4);
        let mut tris = Vec::with_capacity(bands.0 * bands.1 * 2);
        let lat_step = f32::consts::PI / (bands.0 as f32);
        let lng_step = f32::consts::PI * 2.0 / (bands.1 as f32);

        for i in 0..bands.0 {
            let lat_angle = (i as f32) * lat_step;
            let (lat_sin, y1) = lat_angle.sin_cos();
            let (lat_sin2, y2) = (lat_angle + lat_step).sin_cos();

            for j in 0..bands.1 {
                let lng_angle = (j as f32) * lng_step;
                let (lng_sin, lng_cos) = lng_angle.sin_cos();
                let (lng_sin2, lng_cos2) = (lng_angle + lng_step).sin_cos();

                let x1 = lat_sin * lng_cos;
                let x2 = lat_sin * lng_cos2;
                let x3 = lat_sin2 * lng_cos;
                let x4 = lat_sin2 * lng_cos2;

                let z1 = lat_sin * lng_sin;
                let z2 = lat_sin * lng_sin2;
                let z3 = lat_sin2 * lng_sin;
                let z4 = lat_sin2 * lng_sin2;

                // texcoords
                // let u1 = 1.0 - (j as f32) / (bands.1 as f32);
                // let u2 = 1.0 - (j as f32 + 1.0) / (bands.1 as f32);

                // let v1 = 1.0 - (i as f32) / (bands.0 as f32);
                // let v2 = 1.0 - (i as f32 + 1.0) / (bands.0 as f32);

                let k = vertices.len() as u16;
                vertices.extend(&[
                    // normals are same without * radius
                    vec3(x1, y1, z1) * radius,
                    vec3(x2, y1, z2) * radius,
                    vec3(x3, y2, z3) * radius,
                    vec3(x4, y2, z4) * radius,
                ]);

                tris.extend(&[
                    [k + 0, k + 1, k + 2],
                    [k + 2, k + 1, k + 3],
                ]);
            }
        }
        Shape { vertices, tris }
    }
    // ....
}