Example for using drag and drop in 3d

examples/drag_and_drop3d.rs

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+use bevy::prelude::*;
+use bevy_mod_picking::prelude::*;
+use std::f32::consts::FRAC_PI_2;
+
+fn main() {
+    let mut app = App::new();
+    app.add_plugins((
+        DefaultPlugins.set(low_latency_window_plugin()),
+        DefaultPickingPlugins,
+        SpinPlugin,
+    ))
+    .insert_resource(DebugPickingMode::Normal)
+    .add_systems(Startup, setup);
+    #[cfg(feature = "backend_egui")]
+    app.add_plugins(bevy_egui::EguiPlugin);
+    app.run();
+}
+
+/// Set up a simple 3D scene
+fn setup(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+) {
+    // Spawn camera
+    commands.spawn(Camera3dBundle {
+        transform: Transform::from_xyz(0.0, 1200.0, -400.0).looking_at(Vec3::ZERO, Vec3::Y),
+        ..default()
+    });
+    // Spawn cubes
+    for x in -2..=2 {
+        let z = 0.5 + x as f32 * 0.1;
+        commands.spawn((
+            PbrBundle {
+                mesh: meshes.add(Cuboid::default()).into(),
+                transform: Transform::from_xyz(x as f32 * 200.0, 0.0, z)
+                    .with_scale(Vec3::splat(100.)),
+                material: materials.add(Color::hsl(0.0, 1.0, z)),
+                ..default()
+            },
+            PickableBundle::default(), // <- Makes the mesh pickable.
+            On::<Pointer<DragStart>>::target_insert(Pickable::IGNORE), // Disable picking
+            On::<Pointer<DragEnd>>::target_insert(Pickable::default()), // Re-enable picking
+            On::<Pointer<Drag>>::run(on_drag),
+            On::<Pointer<Drop>>::commands_mut(|event, commands| {
+                commands.entity(event.dropped).insert(Spin(FRAC_PI_2)); // Spin dropped entity
+                commands.entity(event.target).insert(Spin(-FRAC_PI_2)); // Spin dropped-on entity
+            }),
+        ));
+    }
+}
+
+fn on_drag(
+    listener: Listener<Pointer<Drag>>,
+    mut transforms: Query<(&mut Transform, &GlobalTransform)>,
+    windows: Query<Entity, With<bevy::window::PrimaryWindow>>,
+    cameras: Query<(&Camera, &GlobalTransform)>,
+) {
+    let Ok(primary_window) = windows.get_single() else {
+        return;
+    };
+    let target = &listener.pointer_location.target;
+    let Some((cam, cam_trans)) = cameras.iter().find(|(c, _)| {
+        c.is_active && c.target.normalize(Some(primary_window)).as_ref() == Some(target)
+    }) else {
+        return;
+    };
+
+    let Ok((mut t, gt)) = transforms.get_mut(listener.target) else {
+        return;
+    };
+    let Some(prev) = cam.world_to_viewport(cam_trans, gt.translation()) else {
+        return;
+    };
+
+    let new = prev + listener.event.delta;
+    let Some(ray) = cam.viewport_to_world(cam_trans, new) else {
+        return;
+    };
+    if let Some(dist) = ray.intersect_plane(Vec3::Y, InfinitePlane3d { normal: Dir3::Y }) {
+        t.translation += ray.get_point(dist) - gt.translation();
+    }
+}
+
+pub struct SpinPlugin;
+
+impl Plugin for SpinPlugin {
+    fn build(&self, app: &mut App) {
+        app.add_systems(Update, spin)
+            .add_systems(Update, spin_cleanup);
+    }
+}
+
+#[derive(Component)]
+struct Spin(f32);
+
+fn spin(mut square: Query<(&mut Spin, &mut Transform)>) {
+    for (mut spin, mut transform) in square.iter_mut() {
+        transform.rotation = Quat::from_rotation_z(spin.0);
+        let delta = -spin.0.clamp(-1.0, 1.0) * 0.05;
+        spin.0 += delta;
+    }
+}
+
+fn spin_cleanup(mut square: Query<(Entity, &Spin, &mut Transform)>, mut commands: Commands) {
+    for (entity, spin, mut transform) in square.iter_mut() {
+        if spin.0.abs().le(&0.001) {
+            transform.rotation = Quat::default(); // <- reset the rotation to zero when it's visually neglible
+            commands.entity(entity).remove::<Spin>(); // <- remove the component so it's stopped updating
+        }
+    }
+}