use std::{f32::consts::PI, ops::Range};  use bevy::{camera::ScalingMode, input::mouse::AccumulatedMouseScroll, prelude::*};  #[derive(Debug, Resource)] struct CameraSettings {     /// The height of the viewport in world units when the orthographic camera's scale is 1     pub orthographic_viewport_height: f32,     /// Clamp the orthographic camera's scale to this range     pub orthographic_zoom_range: Range<f32>,     /// Multiply mouse wheel inputs by this factor when using the orthographic camera     pub orthographic_zoom_speed: f32,     /// Clamp perspective camera's field of view to this range     pub perspective_zoom_range: Range<f32>,     /// Multiply mouse wheel inputs by this factor when using the perspective camera     pub perspective_zoom_speed: f32, }  fn main() {     App::new()         .add_plugins(DefaultPlugins)         .insert_resource(CameraSettings {             orthographic_viewport_height: 5.,             // In orthographic projections, we specify camera scale relative to a default value of 1,             // in which one unit in world space corresponds to one pixel.             orthographic_zoom_range: 0.1..10.0,             // This value was hand-tuned to ensure that zooming in and out feels smooth but not slow.             orthographic_zoom_speed: 0.2,             // Perspective projections use field of view, expressed in radians. We would             // normally not set it to more than π, which represents a 180° FOV.             perspective_zoom_range: (PI / 5.)..(PI - 0.2),             // Changes in FOV are much more noticeable due to its limited range in radians             perspective_zoom_speed: 0.05,         })         .add_systems(Startup, (setup, instructions))         .add_systems(Update, (switch_projection, zoom))         .run(); }  /// Set up a simple 3D scene fn setup(     asset_server: Res<AssetServer>,     camera_settings: Res<CameraSettings>,     mut commands: Commands,     mut meshes: ResMut<Assets<Mesh>>,     mut materials: ResMut<Assets<StandardMaterial>>, ) {     commands.spawn((         Name::new("Camera"),         Camera3d::default(),         Projection::from(OrthographicProjection {             // We can set the scaling mode to FixedVertical to keep the viewport height constant as its aspect ratio changes.             // The viewport height is the height of the camera's view in world units when the scale is 1.             scaling_mode: ScalingMode::FixedVertical {                 viewport_height: camera_settings.orthographic_viewport_height,             },             // This is the default value for scale for orthographic projections.             // To zoom in and out, change this value, rather than `ScalingMode` or the camera's position.             scale: 1.,             ..OrthographicProjection::default_3d()         }),         Transform::from_xyz(5.0, 5.0, 5.0).looking_at(Vec3::ZERO, Vec3::Y),     ));      commands.spawn((         Name::new("Plane"),         Mesh3d(meshes.add(Plane3d::default().mesh().size(5.0, 5.0))),         MeshMaterial3d(materials.add(StandardMaterial {             base_color: Color::srgb(0.3, 0.5, 0.3),             // Turning off culling keeps the plane visible when viewed from beneath.             cull_mode: None,             ..default()         })),     ));      commands.spawn((         Name::new("Fox"),         SceneRoot(             asset_server.load(GltfAssetLabel::Scene(0).from_asset("models/animated/Fox.glb")),         ),         // Note: the scale adjustment is purely an accident of our fox model, which renders         // HUGE unless mitigated!         Transform::from_translation(Vec3::splat(0.0)).with_scale(Vec3::splat(0.025)),     ));      commands.spawn((         Name::new("Light"),         PointLight::default(),         Transform::from_xyz(3.0, 8.0, 5.0),     )); }  fn instructions(mut commands: Commands) {     commands.spawn((         Name::new("Instructions"),         Text::new(             "Scroll mouse wheel to zoom in/out\n\             Space: switch between orthographic and perspective projections",         ),         Node {             position_type: PositionType::Absolute,             top: px(12),             left: px(12),             ..default()         },     )); }  fn switch_projection(     mut camera: Single<&mut Projection, With<Camera>>,     camera_settings: Res<CameraSettings>,     keyboard_input: Res<ButtonInput<KeyCode>>, ) {     if keyboard_input.just_pressed(KeyCode::Space) {         // Switch projection type         **camera = match **camera {             Projection::Orthographic(_) => Projection::Perspective(PerspectiveProjection {                 fov: camera_settings.perspective_zoom_range.start,                 ..default()             }),             Projection::Perspective(_) => Projection::Orthographic(OrthographicProjection {                 scaling_mode: ScalingMode::FixedVertical {                     viewport_height: camera_settings.orthographic_viewport_height,                 },                 ..OrthographicProjection::default_3d()             }),             _ => return,         }     } }  fn zoom(     camera: Single<&mut Projection, With<Camera>>,     camera_settings: Res<CameraSettings>,     mouse_wheel_input: Res<AccumulatedMouseScroll>, ) {     // Usually, you won't need to handle both types of projection,     // but doing so makes for a more complete example.     match *camera.into_inner() {         Projection::Orthographic(ref mut orthographic) => {             // We want scrolling up to zoom in, decreasing the scale, so we negate the delta.             let delta_zoom = -mouse_wheel_input.delta.y * camera_settings.orthographic_zoom_speed;             // When changing scales, logarithmic changes are more intuitive.             // To get this effect, we add 1 to the delta, so that a delta of 0             // results in no multiplicative effect, positive values result in a multiplicative increase,             // and negative values result in multiplicative decreases.             let multiplicative_zoom = 1. + delta_zoom;              orthographic.scale = (orthographic.scale * multiplicative_zoom).clamp(                 camera_settings.orthographic_zoom_range.start,                 camera_settings.orthographic_zoom_range.end,             );         }         Projection::Perspective(ref mut perspective) => {             // We want scrolling up to zoom in, decreasing the scale, so we negate the delta.             let delta_zoom = -mouse_wheel_input.delta.y * camera_settings.perspective_zoom_speed;              // Adjust the field of view, but keep it within our stated range.             perspective.fov = (perspective.fov + delta_zoom).clamp(                 camera_settings.perspective_zoom_range.start,                 camera_settings.perspective_zoom_range.end,             );         }         _ => (),     } }