bevy camera 2d drag/zoom with picking observers

main.rs

use bevy::prelude::*;
fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .run();
}
fn setup(mut commands: Commands, window: Single<Entity, With<Window>>) {
    commands.spawn(Camera2d);
    commands.entity(*window).observe(camera_drag).observe(zoom);
    commands.spawn(Sprite::from_color(Color::WHITE, Vec2::splat(15.)));
}
fn camera_drag(
    drag: Trigger<Pointer<Drag>>,
    mut cam: Single<(&Camera, &GlobalTransform, &mut Transform)>,
) -> Result {
    let mut cam_viewport = cam.0.world_to_viewport(cam.1, cam.2.translation)?;
    cam_viewport += drag.delta * -1.; // inverted feels more natural
    cam.2.translation = cam.0.viewport_to_world_2d(cam.1, cam_viewport)?.extend(0.0);
    Ok(())
}
fn zoom(scroll: Trigger<Pointer<Scroll>>, proj: Single<&mut Projection, With<Camera>>) {
    if let Projection::Orthographic(ref mut proj) = *proj.into_inner() {
        proj.scale *= 1. - (scroll.y / 5.);
    }
}