cyber_rider/src/geometry.rs

use bevy::{
    prelude::{shape::Icosphere, *},
    render::mesh::Indices,
};
use hexasphere::shapes::IcoSphere;
use noise::{HybridMulti, NoiseFn, Perlin};
use wgpu::PrimitiveTopology;

use crate::Label;

pub const PLANET_RADIUS: f32 = 860.0;
pub(crate) const SPAWN_ALTITUDE: f32 = PLANET_RADIUS + 2.0;

#[derive(Component, Debug)]
pub struct CyberBike;

#[derive(Component)]
pub struct CyberSphere;

fn spawn_giant_sphere(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    let color = Color::DARK_GRAY;
    let isphere = shape::Icosphere {
        radius: PLANET_RADIUS,
        subdivisions: 26,
    };

    let pmesh = gen_planet(isphere);

    commands
        .spawn_bundle(PbrBundle {
            mesh: meshes.add(pmesh),
            material: materials.add(StandardMaterial {
                base_color: color,
                metallic: 0.1,
                perceptual_roughness: 0.3,
                alpha_mode: AlphaMode::Blend,
                ..Default::default()
            }),

            ..Default::default()
        })
        .insert(CyberSphere);
}

fn spawn_cyberbike(mut commands: Commands, asset_server: Res<AssetServer>) {
    commands
        .spawn_bundle((
            Transform {
                translation: Vec3::new(SPAWN_ALTITUDE, 0.0, 0.0),
                ..Default::default()
            }
            .looking_at(Vec3::new(PLANET_RADIUS, 1000.0, 0.0), Vec3::X),
            GlobalTransform::identity(),
        ))
        .with_children(|rider| {
            rider.spawn_scene(asset_server.load("cyber-bike_no_y_up.glb#Scene0"));
        })
        .insert(CyberBike);
}

pub struct CyberGeomPlugin;
impl Plugin for CyberGeomPlugin {
    fn build(&self, app: &mut App) {
        app.add_startup_system(spawn_giant_sphere.label(Label::Geometry))
            .add_startup_system(spawn_cyberbike.label(Label::Geometry));
    }
}

//---------------------------------------------------------------------
// utils
//---------------------------------------------------------------------

fn gen_planet(sphere: Icosphere) -> Mesh {
    // straight-up stolen from Bevy's impl of Mesh from Icosphere, so I can do the
    // displacement before normals are calculated.
    let generated = IcoSphere::new(sphere.subdivisions, |point| {
        let inclination = point.y.acos();
        let azimuth = point.z.atan2(point.x);

        let norm_inclination = inclination / std::f32::consts::PI;
        let norm_azimuth = 0.5 - (azimuth / std::f32::consts::TAU);

        [norm_azimuth, norm_inclination]
    });

    // TODO: use displaced points for normals by replacing raw_points with
    // noise-displaced points.
    let noise = HybridMulti::<Perlin>::default();

    let raw_points = generated
        .raw_points()
        .iter()
        .map(|&p| {
            let disp = noise.get(p.as_dvec3().into()) as f32 * 0.07;
            let pt = p + disp;
            pt.into()
        })
        .collect::<Vec<[f32; 3]>>();

    let points = raw_points
        .iter()
        .map(|&p| (Vec3::from_slice(&p) * sphere.radius).into())
        .collect::<Vec<[f32; 3]>>();

    let normals = raw_points
        .iter()
        .copied()
        .map(Into::into)
        .collect::<Vec<[f32; 3]>>();

    let uvs = generated.raw_data().to_owned();

    let mut indices = Vec::with_capacity(generated.indices_per_main_triangle() * 20);

    for i in 0..20 {
        generated.get_indices(i, &mut indices);
    }

    let indices = Indices::U32(indices);

    let mut mesh = Mesh::new(PrimitiveTopology::TriangleList);
    mesh.set_indices(Some(indices));
    mesh.set_attribute(Mesh::ATTRIBUTE_POSITION, points);
    mesh.set_attribute(Mesh::ATTRIBUTE_NORMAL, normals);
    mesh.set_attribute(Mesh::ATTRIBUTE_UV_0, uvs);
    mesh
}