double sided, no backface culling

main.rs

use std::f32::consts::PI;

use bevy::prelude::*;

fn main() -> AppExit {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, startup)
        .add_systems(FixedUpdate, update)
        .run()
}

#[derive(Component)]
struct Rotate;

fn startup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    commands.spawn((
        Mesh3d(
            meshes.add(Plane3d::new(
                Vec3::Y,
                Vec2::splat(10.),
            )),
        ),
        MeshMaterial3d(materials.add(StandardMaterial {
            cull_mode: None,
            double_sided: true,
            ..default()
        })),
        Transform::from_rotation(Quat::from_rotation_x(
            -std::f32::consts::FRAC_PI_2,
        )),
        Rotate,
    ));
    // cube
    commands.spawn((
        Mesh3d(meshes.add(Cuboid::new(1.0, 1.0, 1.0))),
        MeshMaterial3d(
            materials.add(Color::srgb_u8(124, 144, 255)),
        ),
        Transform::from_xyz(0.0, 0.5, 0.0),
    ));
    // light
    commands.spawn((
        PointLight {
            shadows_enabled: true,
            ..default()
        },
        Transform::from_xyz(4.0, 8.0, 4.0),
    ));
    // camera
    commands.spawn((
        Camera3d::default(),
        Transform::from_xyz(-2.5, 4.5, 9.0)
            .looking_at(Vec3::ZERO, Vec3::Y),
    ));
}

fn update(
    mut query: Query<&mut Transform, With<Rotate>>,
    time: Res<Time>,
) {
    for mut transform in &mut query {
        transform.rotate_x(PI * time.delta_secs());
    }
}