use bevy::{camera::ScalingMode, prelude::*};  fn main() {     App::new()         .add_plugins(DefaultPlugins)         .add_systems(Startup, setup)         .run(); }  /// set up a simple 3D scene fn setup(     mut commands: Commands,     mut meshes: ResMut<Assets<Mesh>>,     mut materials: ResMut<Assets<StandardMaterial>>, ) {     // camera     commands.spawn((         Camera3d::default(),         Projection::from(OrthographicProjection {             // 6 world units per pixel of window height.             scaling_mode: ScalingMode::FixedVertical {                 viewport_height: 6.0,             },             ..OrthographicProjection::default_3d()         }),         Transform::from_xyz(5.0, 5.0, 5.0).looking_at(Vec3::ZERO, Vec3::Y),     ));      // plane     commands.spawn((         Mesh3d(meshes.add(Plane3d::default().mesh().size(5.0, 5.0))),         MeshMaterial3d(materials.add(Color::srgb(0.3, 0.5, 0.3))),     ));     // cubes     commands.spawn((         Mesh3d(meshes.add(Cuboid::default())),         MeshMaterial3d(materials.add(Color::srgb(0.8, 0.7, 0.6))),         Transform::from_xyz(1.5, 0.5, 1.5),     ));     commands.spawn((         Mesh3d(meshes.add(Cuboid::default())),         MeshMaterial3d(materials.add(Color::srgb(0.8, 0.7, 0.6))),         Transform::from_xyz(1.5, 0.5, -1.5),     ));     commands.spawn((         Mesh3d(meshes.add(Cuboid::default())),         MeshMaterial3d(materials.add(Color::srgb(0.8, 0.7, 0.6))),         Transform::from_xyz(-1.5, 0.5, 1.5),     ));     commands.spawn((         Mesh3d(meshes.add(Cuboid::default())),         MeshMaterial3d(materials.add(Color::srgb(0.8, 0.7, 0.6))),         Transform::from_xyz(-1.5, 0.5, -1.5),     ));     // light     commands.spawn((PointLight::default(), Transform::from_xyz(3.0, 8.0, 5.0))); }