Mirrors/bevy
2
0
Fork 0
mirror of https://github.com/bevyengine/bevy synced 2025-02-18 15:08:36 +00:00
Code Issues Projects Releases Packages Wiki Activity
bevy/examples/games/desk_toy.rs
Carter Anderson ea578415e1
Improved Spawn APIs and Bundle Effects (#17521) 
## Objective

A major critique of Bevy at the moment is how boilerplatey it is to
compose (and read) entity hierarchies:

```rust
commands
    .spawn(Foo)
    .with_children(|p| {
        p.spawn(Bar).with_children(|p| {
            p.spawn(Baz);
        });
        p.spawn(Bar).with_children(|p| {
            p.spawn(Baz);
        });
    });
```

There is also currently no good way to statically define and return an
entity hierarchy from a function. Instead, people often do this
"internally" with a Commands function that returns nothing, making it
impossible to spawn the hierarchy in other cases (direct World spawns,
ChildSpawner, etc).

Additionally, because this style of API results in creating the
hierarchy bits _after_ the initial spawn of a bundle, it causes ECS
archetype changes (and often expensive table moves).

Because children are initialized after the fact, we also can't count
them to pre-allocate space. This means each time a child inserts itself,
it has a high chance of overflowing the currently allocated capacity in
the `RelationshipTarget` collection, causing literal worst-case
reallocations.

We can do better!

## Solution

The Bundle trait has been extended to support an optional
`BundleEffect`. This is applied directly to World immediately _after_
the Bundle has fully inserted. Note that this is
[intentionally](https://github.com/bevyengine/bevy/discussions/16920)
_not done via a deferred Command_, which would require repeatedly
copying each remaining subtree of the hierarchy to a new command as we
walk down the tree (_not_ good performance).

This allows us to implement the new `SpawnRelated` trait for all
`RelationshipTarget` impls, which looks like this in practice:

```rust
world.spawn((
    Foo,
    Children::spawn((
        Spawn((
            Bar,
            Children::spawn(Spawn(Baz)),
        )),
        Spawn((
            Bar,
            Children::spawn(Spawn(Baz)),
        )),
    ))
))
```

`Children::spawn` returns `SpawnRelatedBundle<Children, L:
SpawnableList>`, which is a `Bundle` that inserts `Children`
(preallocated to the size of the `SpawnableList::size_hint()`).
`Spawn<B: Bundle>(pub B)` implements `SpawnableList` with a size of 1.
`SpawnableList` is also implemented for tuples of `SpawnableList` (same
general pattern as the Bundle impl).

There are currently three built-in `SpawnableList` implementations:

```rust
world.spawn((
    Foo,
    Children::spawn((
        Spawn(Name::new("Child1")),   
        SpawnIter(["Child2", "Child3"].into_iter().map(Name::new),
        SpawnWith(|parent: &mut ChildSpawner| {
            parent.spawn(Name::new("Child4"));
            parent.spawn(Name::new("Child5"));
        })
    )),
))
```

We get the benefits of "structured init", but we have nice flexibility
where it is required!

Some readers' first instinct might be to try to remove the need for the
`Spawn` wrapper. This is impossible in the Rust type system, as a tuple
of "child Bundles to be spawned" and a "tuple of Components to be added
via a single Bundle" is ambiguous in the Rust type system. There are two
ways to resolve that ambiguity:

1. By adding support for variadics to the Rust type system (removing the
need for nested bundles). This is out of scope for this PR :)
2. Using wrapper types to resolve the ambiguity (this is what I did in
this PR).

For the single-entity spawn cases, `Children::spawn_one` does also
exist, which removes the need for the wrapper:

```rust
world.spawn((
    Foo,
    Children::spawn_one(Bar),
))
```

## This works for all Relationships

This API isn't just for `Children` / `ChildOf` relationships. It works
for any relationship type, and they can be mixed and matched!

```rust
world.spawn((
    Foo,
    Observers::spawn((
        Spawn(Observer::new(|trigger: Trigger<FuseLit>| {})),
        Spawn(Observer::new(|trigger: Trigger<Exploded>| {})),
    )),
    OwnerOf::spawn(Spawn(Bar))
    Children::spawn(Spawn(Baz))
))
```

## Macros

While `Spawn` is necessary to satisfy the type system, we _can_ remove
the need to express it via macros. The example above can be expressed
more succinctly using the new `children![X]` macro, which internally
produces `Children::spawn(Spawn(X))`:

```rust
world.spawn((
    Foo,
    children![
        (
            Bar,
            children![Baz],
        ),
        (
            Bar,
            children![Baz],
        ),
    ]
))
```

There is also a `related!` macro, which is a generic version of the
`children!` macro that supports any relationship type:

```rust
world.spawn((
    Foo,
    related!(Children[
        (
            Bar,
            related!(Children[Baz]),
        ),
        (
            Bar,
            related!(Children[Baz]),
        ),
    ])
))
```

## Returning Hierarchies from Functions

Thanks to these changes, the following pattern is now possible:

```rust
fn button(text: &str, color: Color) -> impl Bundle {
    (
        Node {
            width: Val::Px(300.),
            height: Val::Px(100.),
            ..default()
        },
        BackgroundColor(color),
        children![
            Text::new(text),
        ]
    )
}

fn ui() -> impl Bundle {
    (
        Node {
            width: Val::Percent(100.0),
            height: Val::Percent(100.0),
            ..default(),
        },
        children![
            button("hello", BLUE),
            button("world", RED),
        ]
    )
}

// spawn from a system
fn system(mut commands: Commands) {
    commands.spawn(ui());
}

// spawn directly on World
world.spawn(ui());
```

## Additional Changes and Notes

* `Bundle::from_components` has been split out into
`BundleFromComponents::from_components`, enabling us to implement
`Bundle` for types that cannot be "taken" from the ECS (such as the new
`SpawnRelatedBundle`).
* The `NoBundleEffect` trait (which implements `BundleEffect`) is
implemented for empty tuples (and tuples of empty tuples), which allows
us to constrain APIs to only accept bundles that do not have effects.
This is critical because the current batch spawn APIs cannot efficiently
apply BundleEffects in their current form (as doing so in-place could
invalidate the cached raw pointers). We could consider allocating a
buffer of the effects to be applied later, but that does have
performance implications that could offset the balance and value of the
batched APIs (and would likely require some refactors to the underlying
code). I've decided to be conservative here. We can consider relaxing
that requirement on those APIs later, but that should be done in a
followup imo.
* I've ported a few examples to illustrate real-world usage. I think in
a followup we should port all examples to the `children!` form whenever
possible (and for cases that require things like SpawnIter, use the raw
APIs).
* Some may ask "why not use the `Relationship` to spawn (ex:
`ChildOf::spawn(Foo)`) instead of the `RelationshipTarget` (ex:
`Children::spawn(Spawn(Foo))`)?". That _would_ allow us to remove the
`Spawn` wrapper. I've explicitly chosen to disallow this pattern.
`Bundle::Effect` has the ability to create _significant_ weirdness.
Things in `Bundle` position look like components. For example
`world.spawn((Foo, ChildOf::spawn(Bar)))` _looks and reads_ like Foo is
a child of Bar. `ChildOf` is in Foo's "component position" but it is not
a component on Foo. This is a huge problem. Now that `Bundle::Effect`
exists, we should be _very_ principled about keeping the "weird and
unintuitive behavior" to a minimum. Things that read like components
_should be the components they appear to be".

## Remaining Work

* The macros are currently trivially implemented using macro_rules and
are currently limited to the max tuple length. They will require a
proc_macro implementation to work around the tuple length limit.

## Next Steps

* Port the remaining examples to use `children!` where possible and raw
`Spawn` / `SpawnIter` / `SpawnWith` where the flexibility of the raw API
is required.

## Migration Guide

Existing spawn patterns will continue to work as expected.

Manual Bundle implementations now require a `BundleEffect` associated
type. Exisiting bundles would have no bundle effect, so use `()`.
Additionally `Bundle::from_components` has been moved to the new
`BundleFromComponents` trait.

```rust
// Before
unsafe impl Bundle for X {
    unsafe fn from_components<T, F>(ctx: &mut T, func: &mut F) -> Self {
    }
    /* remaining bundle impl here */
}

// After
unsafe impl Bundle for X {
    type Effect = ();
    /* remaining bundle impl here */
}

unsafe impl BundleFromComponents for X {
    unsafe fn from_components<T, F>(ctx: &mut T, func: &mut F) -> Self {
    }
}
```

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
Co-authored-by: Gino Valente <49806985+MrGVSV@users.noreply.github.com>
Co-authored-by: Emerson Coskey <emerson@coskey.dev>
2025-02-09 23:32:56 +00:00

381 lines
14 KiB
Rust
Raw Permalink Blame History

//! Bevy logo as a desk toy using transparent windows! Now with Googly Eyes!
//!
//! This example demonstrates:
//! - Transparent windows that can be clicked through.
//! - Drag-and-drop operations in 2D.
//! - Using entity hierarchy, Transform, and Visibility to create simple animations.
//! - Creating simple 2D meshes based on shape primitives.
use bevy::{
app::AppExit,
input::common_conditions::{input_just_pressed, input_just_released},
prelude::*,
window::{PrimaryWindow, WindowLevel},
};
#[cfg(target_os = "macos")]
use bevy::window::CompositeAlphaMode;
fn main() {
App::new()
.add_plugins(DefaultPlugins.set(WindowPlugin {
primary_window: Some(Window {
title: "Bevy Desk Toy".into(),
transparent: true,
#[cfg(target_os = "macos")]
composite_alpha_mode: CompositeAlphaMode::PostMultiplied,
..default()
}),
..default()
}))
.insert_resource(ClearColor(WINDOW_CLEAR_COLOR))
.insert_resource(WindowTransparency(false))
.insert_resource(CursorWorldPos(None))
.add_systems(Startup, setup)
.add_systems(
Update,
(
get_cursor_world_pos,
update_cursor_hit_test,
(
start_drag.run_if(input_just_pressed(MouseButton::Left)),
end_drag.run_if(input_just_released(MouseButton::Left)),
drag.run_if(resource_exists::<DragOperation>),
quit.run_if(input_just_pressed(MouseButton::Right)),
toggle_transparency.run_if(input_just_pressed(KeyCode::Space)),
move_pupils.after(drag),
),
)
.chain(),
)
.run();
}
/// Whether the window is transparent
#[derive(Resource)]
struct WindowTransparency(bool);
/// The projected 2D world coordinates of the cursor (if it's within primary window bounds).
#[derive(Resource)]
struct CursorWorldPos(Option<Vec2>);
/// The current drag operation including the offset with which we grabbed the Bevy logo.
#[derive(Resource)]
struct DragOperation(Vec2);
/// Marker component for the instructions text entity.
#[derive(Component)]
struct InstructionsText;
/// Marker component for the Bevy logo entity.
#[derive(Component)]
struct BevyLogo;
/// Component for the moving pupil entity (the moving part of the googly eye).
#[derive(Component)]
struct Pupil {
/// Radius of the eye containing the pupil.
eye_radius: f32,
/// Radius of the pupil.
pupil_radius: f32,
/// Current velocity of the pupil.
velocity: Vec2,
}
// Dimensions are based on: assets/branding/icon.png
// Bevy logo radius
const BEVY_LOGO_RADIUS: f32 = 128.0;
// Birds' eyes x y (offset from the origin) and radius
// These values are manually determined from the logo image
const BIRDS_EYES: [(f32, f32, f32); 3] = [
(145.0 - 128.0, -(56.0 - 128.0), 12.0),
(198.0 - 128.0, -(87.0 - 128.0), 10.0),
(222.0 - 128.0, -(140.0 - 128.0), 8.0),
];
const WINDOW_CLEAR_COLOR: Color = Color::srgb(0.2, 0.2, 0.2);
/// Spawn the scene
fn setup(
mut commands: Commands,
asset_server: Res<AssetServer>,
mut meshes: ResMut<Assets<Mesh>>,
mut materials: ResMut<Assets<ColorMaterial>>,
) {
// Spawn a 2D camera
commands.spawn(Camera2d);
// Spawn the text instructions
let font = asset_server.load("fonts/FiraSans-Bold.ttf");
let text_style = TextFont {
font: font.clone(),
font_size: 25.0,
..default()
};
commands.spawn((
Text2d::new("Press Space to play on your desktop! Press it again to return.\nRight click Bevy logo to exit."),
text_style.clone(),
Transform::from_xyz(0.0, -300.0, 100.0),
InstructionsText,
));
// Create a circle mesh. We will reuse this mesh for all our circles.
let circle = meshes.add(Circle { radius: 1.0 });
// Create the different materials we will use for each part of the eyes. For this demo they are basic [`ColorMaterial`]s.
let outline_material = materials.add(Color::BLACK);
let sclera_material = materials.add(Color::WHITE);
let pupil_material = materials.add(Color::srgb(0.2, 0.2, 0.2));
let pupil_highlight_material = materials.add(Color::srgba(1.0, 1.0, 1.0, 0.2));
// Spawn the Bevy logo sprite
commands
.spawn((
Sprite::from_image(asset_server.load("branding/icon.png")),
BevyLogo,
))
.with_children(|commands| {
// For each bird eye
for (x, y, radius) in BIRDS_EYES {
let pupil_radius = radius * 0.6;
let pupil_highlight_radius = radius * 0.3;
let pupil_highlight_offset = radius * 0.3;
// eye outline
commands.spawn((
Mesh2d(circle.clone()),
MeshMaterial2d(outline_material.clone()),
Transform::from_xyz(x, y - 1.0, 1.0)
.with_scale(Vec2::splat(radius + 2.0).extend(1.0)),
));
// sclera
commands.spawn((
Transform::from_xyz(x, y, 2.0),
Visibility::default(),
children![
// sclera
(
Mesh2d(circle.clone()),
MeshMaterial2d(sclera_material.clone()),
Transform::from_scale(Vec3::new(radius, radius, 0.0)),
),
// pupil
(
Transform::from_xyz(0.0, 0.0, 1.0),
Visibility::default(),
Pupil {
eye_radius: radius,
pupil_radius,
velocity: Vec2::ZERO,
},
children![
// pupil main
(
Mesh2d(circle.clone()),
MeshMaterial2d(pupil_material.clone()),
Transform::from_xyz(0.0, 0.0, 0.0).with_scale(Vec3::new(
pupil_radius,
pupil_radius,
1.0,
)),
),
// pupil highlight
(
Mesh2d(circle.clone()),
MeshMaterial2d(pupil_highlight_material.clone()),
Transform::from_xyz(
-pupil_highlight_offset,
pupil_highlight_offset,
1.0,
)
.with_scale(Vec3::new(
pupil_highlight_radius,
pupil_highlight_radius,
1.0,
)),
)
],
)
],
));
}
});
}
/// Project the cursor into the world coordinates and store it in a resource for easy use
fn get_cursor_world_pos(
mut cursor_world_pos: ResMut<CursorWorldPos>,
primary_window: Single<&Window, With<PrimaryWindow>>,
q_camera: Single<(&Camera, &GlobalTransform)>,
) {
let (main_camera, main_camera_transform) = *q_camera;
// Get the cursor position in the world
cursor_world_pos.0 = primary_window.cursor_position().and_then(|cursor_pos| {
main_camera
.viewport_to_world_2d(main_camera_transform, cursor_pos)
.ok()
});
}
/// Update whether the window is clickable or not
fn update_cursor_hit_test(
cursor_world_pos: Res<CursorWorldPos>,
mut primary_window: Single<&mut Window, With<PrimaryWindow>>,
bevy_logo_transform: Single<&Transform, With<BevyLogo>>,
) {
// If the window has decorations (e.g. a border) then it should be clickable
if primary_window.decorations {
primary_window.cursor_options.hit_test = true;
return;
}
// If the cursor is not within the window we don't need to update whether the window is clickable or not
let Some(cursor_world_pos) = cursor_world_pos.0 else {
return;
};
// If the cursor is within the radius of the Bevy logo make the window clickable otherwise the window is not clickable
primary_window.cursor_options.hit_test = bevy_logo_transform
.translation
.truncate()
.distance(cursor_world_pos)
< BEVY_LOGO_RADIUS;
}
/// Start the drag operation and record the offset we started dragging from
fn start_drag(
mut commands: Commands,
cursor_world_pos: Res<CursorWorldPos>,
bevy_logo_transform: Single<&Transform, With<BevyLogo>>,
) {
// If the cursor is not within the primary window skip this system
let Some(cursor_world_pos) = cursor_world_pos.0 else {
return;
};
// Get the offset from the cursor to the Bevy logo sprite
let drag_offset = bevy_logo_transform.translation.truncate() - cursor_world_pos;
// If the cursor is within the Bevy logo radius start the drag operation and remember the offset of the cursor from the origin
if drag_offset.length() < BEVY_LOGO_RADIUS {
commands.insert_resource(DragOperation(drag_offset));
}
}
/// Stop the current drag operation
fn end_drag(mut commands: Commands) {
commands.remove_resource::<DragOperation>();
}
/// Drag the Bevy logo
fn drag(
drag_offset: Res<DragOperation>,
cursor_world_pos: Res<CursorWorldPos>,
time: Res<Time>,
mut bevy_transform: Single<&mut Transform, With<BevyLogo>>,
mut q_pupils: Query<&mut Pupil>,
) {
// If the cursor is not within the primary window skip this system
let Some(cursor_world_pos) = cursor_world_pos.0 else {
return;
};
// Calculate the new translation of the Bevy logo based on cursor and drag offset
let new_translation = cursor_world_pos + drag_offset.0;
// Calculate how fast we are dragging the Bevy logo (unit/second)
let drag_velocity =
(new_translation - bevy_transform.translation.truncate()) / time.delta_secs();
// Update the translation of Bevy logo transform to new translation
bevy_transform.translation = new_translation.extend(bevy_transform.translation.z);
// Add the cursor drag velocity in the opposite direction to each pupil.
// Remember pupils are using local coordinates to move. So when the Bevy logo moves right they need to move left to
// simulate inertia, otherwise they will move fixed to the parent.
for mut pupil in &mut q_pupils {
pupil.velocity -= drag_velocity;
}
}
/// Quit when the user right clicks the Bevy logo
fn quit(
cursor_world_pos: Res<CursorWorldPos>,
mut app_exit: EventWriter<AppExit>,
bevy_logo_transform: Single<&Transform, With<BevyLogo>>,
) {
// If the cursor is not within the primary window skip this system
let Some(cursor_world_pos) = cursor_world_pos.0 else {
return;
};
// If the cursor is within the Bevy logo radius send the [`AppExit`] event to quit the app
if bevy_logo_transform
.translation
.truncate()
.distance(cursor_world_pos)
< BEVY_LOGO_RADIUS
{
app_exit.send(AppExit::Success);
}
}
/// Enable transparency for the window and make it on top
fn toggle_transparency(
mut commands: Commands,
mut window_transparency: ResMut<WindowTransparency>,
mut q_instructions_text: Query<&mut Visibility, With<InstructionsText>>,
mut primary_window: Single<&mut Window, With<PrimaryWindow>>,
) {
// Toggle the window transparency resource
window_transparency.0 = !window_transparency.0;
// Show or hide the instructions text
for mut visibility in &mut q_instructions_text {
*visibility = if window_transparency.0 {
Visibility::Hidden
} else {
Visibility::Visible
};
}
// Remove the primary window's decorations (e.g. borders), make it always on top of other desktop windows, and set the clear color to transparent
// only if window transparency is enabled
let clear_color;
(
primary_window.decorations,
primary_window.window_level,
clear_color,
) = if window_transparency.0 {
(false, WindowLevel::AlwaysOnTop, Color::NONE)
} else {
(true, WindowLevel::Normal, WINDOW_CLEAR_COLOR)
};
// Set the clear color
commands.insert_resource(ClearColor(clear_color));
}
/// Move the pupils and bounce them around
fn move_pupils(time: Res<Time>, mut q_pupils: Query<(&mut Pupil, &mut Transform)>) {
for (mut pupil, mut transform) in &mut q_pupils {
// The wiggle radius is how much the pupil can move within the eye
let wiggle_radius = pupil.eye_radius - pupil.pupil_radius;
// Store the Z component
let z = transform.translation.z;
// Truncate the Z component to make the calculations be on [`Vec2`]
let mut translation = transform.translation.truncate();
// Decay the pupil velocity
pupil.velocity *= ops::powf(0.04f32, time.delta_secs());
// Move the pupil
translation += pupil.velocity * time.delta_secs();
// If the pupil hit the outside border of the eye, limit the translation to be within the wiggle radius and invert the velocity.
// This is not physically accurate but it's good enough for the googly eyes effect.
if translation.length() > wiggle_radius {
translation = translation.normalize() * wiggle_radius;
// Invert and decrease the velocity of the pupil when it bounces
pupil.velocity *= -0.75;
}
// Update the entity transform with the new translation after reading the Z component
transform.translation = translation.extend(z);
}
}
Reference in a new issue View git blame Copy permalink