From 432e5a737ab29df30e39f30d8eca074dec317159 Mon Sep 17 00:00:00 2001
From: Leon Liu <leon.liuyang.d@gmail.com>
Date: Thu, 14 Aug 2025 10:00:31 +0900
Subject: [PATCH] update

---
 Cargo.lock             |  54 +++++++++++++
 Cargo.toml             |   1 +
 examples/cam_follow.rs |  87 +++++++++++++++++++++
 src/main.rs            | 169 ++++++++++++++++++++++++++++++-----------
 4 files changed, 268 insertions(+), 43 deletions(-)
 create mode 100644 examples/cam_follow.rs

diff --git a/Cargo.lock b/Cargo.lock
index e5c9c8e..6e6e490 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -154,6 +154,12 @@ version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fc7eb209b1518d6bb87b283c20095f5228ecda460da70b44f0802523dea6da04"
 
+[[package]]
+name = "android-tzdata"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e999941b234f3131b00bc13c22d06e8c5ff726d1b6318ac7eb276997bbb4fef0"
+
 [[package]]
 name = "android_log-sys"
 version = "0.3.2"
@@ -1704,6 +1710,18 @@ version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "613afe47fcd5fac7ccf1db93babcb082c5994d996f20b8b159f2ad1658eb5724"
 
+[[package]]
+name = "chrono"
+version = "0.4.41"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c469d952047f47f91b68d1cba3f10d63c11d73e4636f24f08daf0278abf01c4d"
+dependencies = [
+ "android-tzdata",
+ "iana-time-zone",
+ "num-traits",
+ "windows-link",
+]
+
 [[package]]
 name = "clang-sys"
 version = "1.8.1"
@@ -2663,6 +2681,30 @@ version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "dfa686283ad6dd069f105e5ab091b04c62850d3e4cf5d67debad1933f55023df"
 
+[[package]]
+name = "iana-time-zone"
+version = "0.1.63"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b0c919e5debc312ad217002b8048a17b7d83f80703865bbfcfebb0458b0b27d8"
+dependencies = [
+ "android_system_properties",
+ "core-foundation-sys",
+ "iana-time-zone-haiku",
+ "js-sys",
+ "log",
+ "wasm-bindgen",
+ "windows-core 0.61.2",
+]
+
+[[package]]
+name = "iana-time-zone-haiku"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f31827a206f56af32e590ba56d5d2d085f558508192593743f16b2306495269f"
+dependencies = [
+ "cc",
+]
+
 [[package]]
 name = "image"
 version = "0.25.6"
@@ -2756,6 +2798,17 @@ version = "1.0.15"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4a5f13b858c8d314ee3e8f639011f7ccefe71f97f96e50151fb991f267928e2c"
 
+[[package]]
+name = "iyes_perf_ui"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3e4468c51a47d2422a3a3e01b45cb47ed0fbce520495dd7de495bcfe8ce0f856"
+dependencies = [
+ "bevy",
+ "chrono",
+ "num-traits",
+]
+
 [[package]]
 name = "jni"
 version = "0.21.1"
@@ -4204,6 +4257,7 @@ dependencies = [
  "bevy",
  "bevy-inspector-egui",
  "bevy_panorbit_camera",
+ "iyes_perf_ui",
 ]
 
 [[package]]
diff --git a/Cargo.toml b/Cargo.toml
index 691fb51..0584c5d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,6 +7,7 @@ edition = "2024"
 bevy = "0.16"
 bevy-inspector-egui = "0.33.1"
 bevy_panorbit_camera = "0.26"
+iyes_perf_ui = "0.5.0"
 
 # Enable a small amount of optimization in the dev profile.
 [profile.dev]
diff --git a/examples/cam_follow.rs b/examples/cam_follow.rs
new file mode 100644
index 0000000..16f5334
--- /dev/null
+++ b/examples/cam_follow.rs
@@ -0,0 +1,87 @@
+//! Demonstrates how to have the camera follow a target object
+
+use bevy::prelude::*;
+use bevy_panorbit_camera::{PanOrbitCamera, PanOrbitCameraPlugin};
+use std::f32::consts::TAU;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_plugins(PanOrbitCameraPlugin)
+        .add_systems(Startup, setup)
+        .add_systems(Update, (animate_cube, cam_follow).chain())
+        .run();
+}
+
+#[derive(Component)]
+struct Cube;
+
+fn setup(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+) {
+    // Ground
+    commands.spawn((
+        Mesh3d(meshes.add(Plane3d::default().mesh().size(0.5, 0.5))),
+        MeshMaterial3d(materials.add(Color::srgb(0.3, 0.5, 0.3))),
+    ));
+    // Cube
+    commands
+        .spawn((
+            Mesh3d(meshes.add(Cuboid::new(0.1, 0.1, 0.1))),
+            MeshMaterial3d(materials.add(Color::srgb(0.8, 0.7, 0.6))),
+            Transform::from_xyz(0.0, 0.5, 0.0),
+        ))
+        .insert(Cube);
+    // Light
+    commands.spawn((
+        PointLight {
+            shadows_enabled: true,
+            ..default()
+        },
+        Transform::from_xyz(4.0, 8.0, 4.0),
+    ));
+    // Camera
+    commands.spawn((
+        Transform::from_translation(Vec3::new(0.0, 0.15, 0.5)),
+        PanOrbitCamera {
+            // Panning the camera changes the focus, and so you most likely want to disable
+            // panning when setting the focus manually
+            pan_sensitivity: 0.0,
+            // If you want to fully control the camera's focus, set smoothness to 0 so it
+            // immediately snaps to that location. If you want the 'follow' to be smoothed,
+            // leave this at default or set it to something between 0 and 1.
+            pan_smoothness: 0.0,
+            ..default()
+        },
+    ));
+}
+
+/// Move the cube in a circle around the Y axis
+fn animate_cube(
+    time: Res<Time>,
+    mut cube_q: Query<&mut Transform, With<Cube>>,
+    mut angle: Local<f32>,
+) {
+    if let Ok(mut cube_tfm) = cube_q.single_mut() {
+        // Rotate 20 degrees a second, wrapping around to 0 after a full rotation
+        *angle += 20f32.to_radians() * time.delta_secs() % TAU;
+        // Convert angle to position
+        let pos = Vec3::new(angle.sin() * 0.15, 0.05, angle.cos() * 0.15);
+        cube_tfm.translation = pos;
+    }
+}
+
+/// Set the camera's focus to the cube's position
+fn cam_follow(mut pan_orbit_q: Query<&mut PanOrbitCamera>, cube_q: Query<&Transform, With<Cube>>) {
+    if let Ok(mut pan_orbit) = pan_orbit_q.single_mut() {
+        if let Ok(cube_tfm) = cube_q.single() {
+            pan_orbit.target_focus = cube_tfm.translation;
+            // Whenever changing properties manually like this, it's necessary to force
+            // PanOrbitCamera to update this frame (by default it only updates when there are
+            // input events).
+            pan_orbit.force_update = true;
+        }
+    }
+}
diff --git a/src/main.rs b/src/main.rs
index c055832..a2097fd 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,11 +1,12 @@
 use bevy::{
     core_pipeline::{bloom::Bloom, tonemapping::Tonemapping},
+    input::mouse::{MouseScrollUnit, MouseWheel},
     math::DVec3,
     prelude::*,
-    window::WindowMode,
+    window::{WindowMode, WindowResolution},
 };
 use bevy_inspector_egui::{bevy_egui::EguiPlugin, quick::WorldInspectorPlugin};
-use bevy_panorbit_camera::{PanOrbitCamera, PanOrbitCameraPlugin};
+use iyes_perf_ui::{PerfUiPlugin, prelude::PerfUiAllEntries};
 
 // Scaling factor to convert AU to game units
 // Neptune is approximately 30.1 astronomical units (AU) from the Sun
@@ -55,6 +56,8 @@ struct ObjectBundle {
 
 #[derive(Component)]
 struct Star;
+#[derive(Component)]
+struct Earth;
 
 // Component for UI name labels
 #[derive(Component)]
@@ -66,20 +69,33 @@ struct ObjectLabel {
 #[derive(Component)]
 struct Trackable {}
 
+// Resource to track which entity the camera should follow
+#[derive(Resource)]
+struct CameraFollow {
+    target: Option<Entity>,
+    distance: f32, // Current zoom distance from target
+}
+
 pub struct SolarRenderingPlugin;
 
 impl Plugin for SolarRenderingPlugin {
     fn build(&self, app: &mut App) {
-        app.add_systems(Startup, (setup_rendering, setup_ui))
-            .add_systems(
-                FixedPostUpdate,
-                (
-                    sync_radius_to_mesh,
-                    sync_position_to_transform,
-                    sync_name_labels,
-                ),
-            )
-            .add_systems(Update, (update_label_positions, handle_label_clicks));
+        app.insert_resource(CameraFollow {
+            target: None,
+            distance: 10.0,
+        })
+        .add_systems(Startup, (setup_rendering, setup_ui))
+        .add_systems(
+            FixedPostUpdate,
+            (
+                sync_radius_to_mesh,
+                sync_position_to_transform,
+                sync_name_labels,
+                camera_follow_system.after(sync_position_to_transform),
+            ),
+        )
+        .add_systems(PostUpdate, update_label_positions)
+        .add_systems(Update, (handle_label_clicks, handle_scroll_zoom));
     }
 }
 
@@ -93,8 +109,6 @@ fn sync_radius_to_mesh(
         // Convert AU to game units for rendering
         let render_radius = radius.0.0 * AU_TO_GAME_UNITS;
 
-        println!("render_radius: {:?}", render_radius);
-
         // Create or update sphere mesh
         let sphere_mesh = meshes.add(Sphere::new(render_radius as f32));
         let material = materials.add(if star.is_none() {
@@ -129,7 +143,6 @@ fn sync_position_to_transform(
     for (entity, position, transform) in query.iter_mut() {
         // Convert AU to game units for rendering
         let scaled_position = position.0.0 * AU_TO_GAME_UNITS;
-        println!("scaled_position: {:?}", scaled_position);
         match transform {
             Some(mut t) => {
                 // Update existing transform
@@ -161,13 +174,14 @@ fn setup_rendering(mut commands: Commands) {
         }),
         Tonemapping::TonyMcMapface,
         Transform::from_translation(Vec3::new(0., 0., 10.0)),
-        Bloom::NATURAL,
-        PanOrbitCamera {
-            pan_sensitivity: 0.0, // Disable panning by setting sensitivity to 0
-            focus: Vec3::ZERO,
-            zoom_lower_limit: 1e-8,
-            ..default()
-        },
+        // Bloom::NATURAL,
+        // PanOrbitCamera {
+        //     pan_sensitivity: 0.0, // Disable panning by setting sensitivity to 0
+        //     focus: Vec3::ZERO,
+        //     zoom_lower_limit: 1e-8,
+        //     allow_upside_down: true,
+        //     ..default()
+        // },
     ));
 
     commands.spawn(PointLight {
@@ -175,6 +189,7 @@ fn setup_rendering(mut commands: Commands) {
         shadows_enabled: true,
         ..default()
     });
+    commands.spawn(PerfUiAllEntries::default());
 }
 
 fn setup_ui(mut commands: Commands) {
@@ -225,7 +240,7 @@ fn sync_name_labels(
 
 fn update_label_positions(
     mut label_query: Query<(&mut Node, &ObjectLabel, &mut Text), With<ObjectLabel>>,
-    objects_query: Query<(&Position, &Name, &Radius)>,
+    objects_query: Query<(&GlobalTransform, &Name, &Radius)>,
     camera_query: Query<(&Camera, &GlobalTransform)>,
 ) {
     let Ok((camera, camera_transform)) = camera_query.single() else {
@@ -233,14 +248,12 @@ fn update_label_positions(
     };
 
     for (mut node, label, mut text) in label_query.iter_mut() {
-        if let Ok((position, name, _radius)) = objects_query.get(label.target_entity) {
-            let world_pos = position.0.0 * AU_TO_GAME_UNITS;
-
-            if let Ok(screen_pos) = camera.world_to_viewport(camera_transform, world_pos.as_vec3())
-            {
+        if let Ok((global_transform, name, _radius)) = objects_query.get(label.target_entity) {
+            let world_pos = global_transform.translation();
+            if let Ok(screen_pos) = camera.world_to_viewport(camera_transform, world_pos) {
                 // Position the label on screen, offset slightly to avoid overlapping the object
-                node.left = Val::Px(screen_pos.x + 10.0);
-                node.top = Val::Px(screen_pos.y - 10.0);
+                node.left = Val::Px(screen_pos.x);
+                node.top = Val::Px(screen_pos.y);
 
                 // Update text in case name changed
                 text.0 = name.0.0.clone();
@@ -261,26 +274,87 @@ fn handle_label_clicks(
         (&Interaction, &ObjectLabel),
         (Changed<Interaction>, With<ObjectLabel>),
     >,
-    trackable_objects: Query<(&Position, &Trackable, &Radius)>,
-    mut camera_query: Query<&mut PanOrbitCamera>,
+    trackable_objects: Query<(&Transform, &Trackable, &Radius)>,
+    mut camera_query: Query<&mut Transform, (With<Camera>, Without<Trackable>)>,
+    mut camera_follow: ResMut<CameraFollow>,
 ) {
     for (interaction, label) in interaction_query.iter() {
         if *interaction == Interaction::Pressed {
-            if let Ok((position, _trackable, radius)) = trackable_objects.get(label.target_entity) {
-                if let Ok(mut pan_orbit) = camera_query.single_mut() {
-                    // Focus camera on the clicked object using target values for smooth transitions
-                    pan_orbit.target_focus = (position.0.0 * AU_TO_GAME_UNITS).as_vec3();
-                    pan_orbit.target_radius = (radius.0.0 * AU_TO_GAME_UNITS) as f32 * 4.;
+            if let Ok((target_transform, _trackable, radius)) =
+                trackable_objects.get(label.target_entity)
+            {
+                if let Ok(mut camera_transform) = camera_query.single_mut() {
+                    let target_world_pos = target_transform.translation;
 
-                    // Also set the immediate values to ensure it takes effect
-                    // pan_orbit.focus = position.0.0.as_vec3();
-                    // pan_orbit.radius = Some(trackable.zoom_distance);
+                    // Calculate appropriate distance based on entity radius (with some padding)
+                    let entity_radius = (radius.0.0 * AU_TO_GAME_UNITS) as f32;
+                    let desired_distance = entity_radius * 16.0; // 8x radius
+
+                    // Position camera at desired distance from target
+                    let camera_direction =
+                        (camera_transform.translation - target_world_pos).normalize();
+                    let new_camera_pos = target_world_pos + camera_direction * desired_distance;
+
+                    camera_transform.translation = new_camera_pos;
+                    camera_transform.look_at(target_world_pos, Vec3::Y);
+
+                    // Set the follow target and initial distance
+                    camera_follow.target = Some(label.target_entity);
+                    camera_follow.distance = desired_distance;
                 }
             }
         }
     }
 }
 
+fn camera_follow_system(
+    camera_follow: Res<CameraFollow>,
+    objects_query: Query<&Transform, With<Trackable>>,
+    mut camera_query: Query<&mut Transform, (With<Camera>, Without<Trackable>)>,
+) {
+    if let Some(target_entity) = camera_follow.target {
+        if let Ok(target_transform) = objects_query.get(target_entity) {
+            if let Ok(mut camera_transform) = camera_query.single_mut() {
+                // Fixed camera direction relative to tracked object (stationary relative position)
+                let fixed_direction = Vec3::new(0.0, 0.0, 1.0);
+
+                // Position camera at the specified distance from target in fixed direction
+                let new_camera_pos =
+                    target_transform.translation + fixed_direction * camera_follow.distance;
+                camera_transform.translation = new_camera_pos;
+
+                // Keep camera looking at the target entity
+                camera_transform.look_at(target_transform.translation, Vec3::Y);
+            }
+        }
+    }
+}
+
+fn handle_scroll_zoom(
+    mut scroll_events: EventReader<MouseWheel>,
+    mut camera_follow: ResMut<CameraFollow>,
+) {
+    for event in scroll_events.read() {
+        let zoom_delta = match event.unit {
+            MouseScrollUnit::Line => event.y * 0.1,
+            MouseScrollUnit::Pixel => event.y * 0.01,
+        };
+
+        // Update zoom distance with limits
+        camera_follow.distance = (camera_follow.distance * (1.0 - zoom_delta)).clamp(1e-9, 100.0);
+    }
+}
+
+fn initialize_camera_follow(
+    earth_query: Query<Entity, (With<Earth>, With<Trackable>)>,
+    mut camera_follow: ResMut<CameraFollow>,
+) {
+    if let Ok(earth) = earth_query.single() {
+        camera_follow.target = Some(earth);
+        camera_follow.distance = 1e-3;
+    }
+}
+
 fn setup_solar_system(mut commands: Commands) {
     // Sun - From NASA JPL Horizons data (J2000.0 epoch)
     // Physical properties: Mass = 1988410 x 10^24 kg, Radius = 695700 km = 0.00465 AU
@@ -316,6 +390,7 @@ fn setup_solar_system(mut commands: Commands) {
             radius: Radius(DistanceAu(0.0000426)), // Mean radius in AU (6371.01 km / 149597870.691)
         },
         Trackable {},
+        Earth,
     ));
 
     // Moon - From NASA JPL Horizons data (A.D. 2000-Jan-01 12:00:00.0000 TDB)
@@ -415,15 +490,23 @@ fn main() {
             primary_window: Some(Window {
                 title: "Solar Sim".to_string(),
                 mode: WindowMode::BorderlessFullscreen(MonitorSelection::Primary),
+                resolution: WindowResolution::default().with_scale_factor_override(2.0),
                 ..default()
             }),
             ..default()
         }))
-        .add_plugins(PanOrbitCameraPlugin)
         .add_plugins(EguiPlugin::default())
         .add_plugins(WorldInspectorPlugin::new())
-        .add_plugins(SolarRenderingPlugin)
-        .add_systems(Startup, setup_solar_system)
+        .add_plugins(SolarRenderingPlugin) // we want Bevy to measure these values for us:
+        .add_plugins(bevy::diagnostic::FrameTimeDiagnosticsPlugin::default())
+        .add_plugins(bevy::diagnostic::EntityCountDiagnosticsPlugin)
+        .add_plugins(bevy::diagnostic::SystemInformationDiagnosticsPlugin)
+        .add_plugins(bevy::render::diagnostic::RenderDiagnosticsPlugin)
+        .add_plugins(PerfUiPlugin)
+        .add_systems(
+            Startup,
+            (setup_solar_system, initialize_camera_follow).chain(),
+        )
         .add_systems(FixedUpdate, n_body)
         .run();
 }