NoEntities even though there clearly are

[getkirill]

so i'm making a tetris clone for myself to practice rust and bevy.
i wanted to get 0, 0 screen coordinates in world space, so i've marked my camera with MainCamera component.
but when i try to run this, it panics with noentities error.

target: wasm32-unknown-unknown

use bevy::prelude::*;
use std::time::Duration;

#[derive(Component)]
struct PieceComponent;

#[derive(Component)]
struct MainCamera;

#[derive(Resource)]
struct InputHoldDelayTimer {
    hold_start_timer: Timer,
    hold_small_delay_timer: Timer,
    held_key: Option<KeyCode>,
}

impl InputHoldDelayTimer {
    fn tick(&mut self, delta: Duration) {
        self.hold_start_timer.tick(delta);
        self.hold_small_delay_timer.tick(delta);
    }
}

#[derive(Resource)]
struct GravityTimer {
    timer: Timer,
}

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_startup_system(spawn_camera)
        .add_startup_system(setup)
        .add_startup_system(spawn_test_piece)
        .add_system(piece_system)
        .run();
}

fn spawn_camera(mut commands: Commands) {
    commands.spawn((Camera2dBundle::default(), MainCamera));
}

fn setup(
    mut commands: Commands,
    asset_server: Res<AssetServer>,
    camera: Query<&Transform, With<MainCamera>>,
    windows: Res<Windows>,
) {
    commands.insert_resource({
        let mut r = InputHoldDelayTimer {
            hold_start_timer: Timer::new(Duration::from_secs_f32(1.0 / 8.0), TimerMode::Once),
            hold_small_delay_timer: Timer::new(
                Duration::from_secs_f32(1.0 / 32.0),
                TimerMode::Repeating,
            ),
            held_key: None,
        };
        r.hold_start_timer.pause();
        r.hold_small_delay_timer.pause();
        r
    });
    commands.insert_resource(GravityTimer {
        timer: Timer::new(Duration::from_secs_f32(0.5), TimerMode::Repeating),
    });
    commands.spawn(SpriteBundle {
        texture: asset_server.load("sprites/chinese/UI.png"),
        transform: Transform::from_translation(window_to_world(
            Vec2 { x: 0.0, y: 0.0 },
            windows.primary(),
            camera.single(),
        )),
        ..default()
    });
}

fn spawn_test_piece(mut commands: Commands, asset_server: Res<AssetServer>) {
    commands.spawn((
        SpriteBundle {
            texture: asset_server.load("sprites/chinese/pieces/L_Piece.png"),
            transform: Transform::from_xyz(-16.0, 32.0 * 6.0, 1.0),
            ..default()
        },
        PieceComponent {},
    ));
}

fn piece_system(
    mut commands: Commands,
    mut piece: Query<(&PieceComponent, &mut Transform)>,
    time: Res<Time>,
    keys: Res<Input<KeyCode>>,
    mut hold_timer: ResMut<InputHoldDelayTimer>,
    mut gravity_timer: ResMut<GravityTimer>,
) {
    for (_, mut transform) in &mut piece {
        if let Some(key) = hold_timer.held_key {
            if !keys.pressed(key) {
                hold_timer.hold_start_timer.pause();
                hold_timer.hold_start_timer.reset();
                hold_timer.hold_small_delay_timer.pause();
                hold_timer.hold_small_delay_timer.reset();
            }
        }
        if hold_timer.hold_start_timer.finished() {
            if hold_timer.hold_small_delay_timer.just_finished() {
                if let Some(key) = hold_timer.held_key {
                    match key {
                        KeyCode::Right => {
                            transform.translation.x += 32.0;
                        }
                        KeyCode::Left => {
                            transform.translation.x -= 32.0;
                        }
                        KeyCode::Down => {
                            transform.translation.y -= 32.0;
                        }
                        _ => {}
                    };
                }
            }
        } else {
            if keys.any_pressed(vec![KeyCode::Right, KeyCode::Left, KeyCode::Down]) {
                hold_timer.hold_start_timer.unpause();
                hold_timer.hold_small_delay_timer.unpause();
            }
            if keys.just_pressed(KeyCode::Right) {
                transform.translation.x += 32.0;
                hold_timer.held_key = Some(KeyCode::Right);
            }
            if keys.just_pressed(KeyCode::Left) {
                transform.translation.x -= 32.0;
                hold_timer.held_key = Some(KeyCode::Left);
            }
            if keys.just_pressed(KeyCode::Down) {
                transform.translation.y -= 32.0;
                hold_timer.held_key = Some(KeyCode::Down);
            }
        }
        if gravity_timer.timer.just_finished() {
            transform.translation.y -= 32.0;
        }
        hold_timer.tick(time.delta());
        gravity_timer.timer.tick(time.delta());
    }
}

// yeeted from stackoverflow
fn window_to_world(position: Vec2, window: &Window, camera: &Transform) -> Vec3 {
    // Center in screen space
    let norm = Vec3::new(
        position.x - window.width() / 2.,
        position.y - window.height() / 2.,
        0.,
    );

    // Apply camera transform
    *camera * norm

    // Alternatively:
    //camera.mul_vec3(norm)
}

Panic message:

panicked at 'called `Result::unwrap()` on an `Err` value: NoEntities("bevy_ecs::query::state::QueryState<&bevy_transform::components::transform::Transform, bevy_ecs::query::filter::With<webtris::MainCamera>>")', src\main.rs:70:20

Stack:

Error
    at imports.wbg.__wbg_new_abda76e883ba8a5f (http://127.0.0.1:1334/api/wasm.js:359:13)
    at __wbg_new_abda76e883ba8a5f externref shim (http://127.0.0.1:1334/api/wasm.wasm:wasm-function[30046]:0xe1de4c)
    at console_error_panic_hook::hook::h6c90415ca7665cfb (http://127.0.0.1:1334/api/wasm.wasm:wasm-function[7147]:0x9bf389)
    at core::ops::function::Fn::call::h865946abbd5b4e41 (http://127.0.0.1:1334/api/wasm.wasm:wasm-function[40850]:0xe4ba7b)
    at std::panicking::rust_panic_with_hook::he04cb00575f2a1e3 (http://127.0.0.1:1334/api/wasm.wasm:wasm-function[15501]:0xc9ea7c)
    at std::panicking::begin_panic_handler::{{closure}}::hb733f0aa505760cf (http://127.0.0.1:1334/api/wasm.wasm:wasm-function[18881]:0xd3e934)
    at std::sys_common::backtrace::__rust_end_short_backtrace::h6beefa0bcab220bc (http://127.0.0.1:1334/api/wasm.wasm:wasm-function[26607]:0xe02821)
    at rust_begin_unwind (http://127.0.0.1:1334/api/wasm.wasm:wasm-function[23164]:0xdc612c)
    at core::panicking::panic_fmt::h586d720a90aa8503 (http://127.0.0.1:1334/api/wasm.wasm:wasm-function[25334]:0xdf1086)
    at core::result::unwrap_failed::h1d03d3774c363770 (http://127.0.0.1:1334/api/wasm.wasm:wasm-function[20917]:0xd898b9)

[jakobhellermann]

Commands are only applied at the end of the stage, so if you have two startup systems, they won't see spawned entities from the other.

You need add_startup_system_to_stage(StartupStage::PostStartup) for the second one, or put the first one in StartupStage::PreStartup.

[getkirill]

got it, fixed. thanks!