forestia/bevy
2
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity
63e0f794d1
bevy/examples/3d/motion_blur.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

392 lines
13 KiB
Rust
Raw Blame History

//! Demonstrates how to enable per-object motion blur. This rendering feature can be configured per
//! camera using the [`MotionBlur`] component.z
use bevy::{
core_pipeline::motion_blur::MotionBlur,
image::{ImageAddressMode, ImageFilterMode, ImageSampler, ImageSamplerDescriptor},
math::ops,
prelude::*,
};
fn main() {
let mut app = App::new();
app.add_plugins(DefaultPlugins)
.add_systems(Startup, (setup_camera, setup_scene, setup_ui))
.add_systems(Update, (keyboard_inputs, move_cars, move_camera).chain())
.run();
}
fn setup_camera(mut commands: Commands) {
commands.spawn((
Camera3d::default(),
// Add the `MotionBlur` component to a camera to enable motion blur.
// Motion blur requires the depth and motion vector prepass, which this bundle adds.
// Configure the amount and quality of motion blur per-camera using this component.
MotionBlur {
shutter_angle: 1.0,
samples: 2,
#[cfg(all(feature = "webgl2", target_arch = "wasm32", not(feature = "webgpu")))]
_webgl2_padding: Default::default(),
},
// MSAA and Motion Blur together are not compatible on WebGL
#[cfg(all(feature = "webgl2", target_arch = "wasm32", not(feature = "webgpu")))]
Msaa::Off,
));
}
// Everything past this point is used to build the example, but isn't required to use motion blur.
#[derive(Resource)]
enum CameraMode {
Track,
Chase,
}
#[derive(Component)]
struct Moves(f32);
#[derive(Component)]
struct CameraTracked;
#[derive(Component)]
struct Rotates;
fn setup_scene(
asset_server: Res<AssetServer>,
mut images: ResMut<Assets<Image>>,
mut commands: Commands,
mut meshes: ResMut<Assets<Mesh>>,
mut materials: ResMut<Assets<StandardMaterial>>,
) {
commands.insert_resource(AmbientLight {
color: Color::WHITE,
brightness: 300.0,
..default()
});
commands.insert_resource(CameraMode::Chase);
commands.spawn((
DirectionalLight {
illuminance: 3_000.0,
shadows_enabled: true,
..default()
},
Transform::default().looking_to(Vec3::new(-1.0, -0.7, -1.0), Vec3::X),
));
// Sky
commands.spawn((
Mesh3d(meshes.add(Sphere::default())),
MeshMaterial3d(materials.add(StandardMaterial {
unlit: true,
base_color: Color::linear_rgb(0.1, 0.6, 1.0),
..default()
})),
Transform::default().with_scale(Vec3::splat(-4000.0)),
));
// Ground
let mut plane: Mesh = Plane3d::default().into();
let uv_size = 4000.0;
let uvs = vec![[uv_size, 0.0], [0.0, 0.0], [0.0, uv_size], [uv_size; 2]];
plane.insert_attribute(Mesh::ATTRIBUTE_UV_0, uvs);
commands.spawn((
Mesh3d(meshes.add(plane)),
MeshMaterial3d(materials.add(StandardMaterial {
base_color: Color::WHITE,
perceptual_roughness: 1.0,
base_color_texture: Some(images.add(uv_debug_texture())),
..default()
})),
Transform::from_xyz(0.0, -0.65, 0.0).with_scale(Vec3::splat(80.)),
));
spawn_cars(&asset_server, &mut meshes, &mut materials, &mut commands);
spawn_trees(&mut meshes, &mut materials, &mut commands);
spawn_barriers(&mut meshes, &mut materials, &mut commands);
}
fn spawn_cars(
asset_server: &AssetServer,
meshes: &mut Assets<Mesh>,
materials: &mut Assets<StandardMaterial>,
commands: &mut Commands,
) {
const N_CARS: usize = 20;
let box_mesh = meshes.add(Cuboid::new(0.3, 0.15, 0.55));
let cylinder = meshes.add(Cylinder::default());
let logo = asset_server.load("branding/icon.png");
let wheel_matl = materials.add(StandardMaterial {
base_color: Color::WHITE,
base_color_texture: Some(logo.clone()),
..default()
});
let mut matl = |color| {
materials.add(StandardMaterial {
base_color: color,
..default()
})
};
let colors = [
matl(Color::linear_rgb(1.0, 0.0, 0.0)),
matl(Color::linear_rgb(1.0, 1.0, 0.0)),
matl(Color::BLACK),
matl(Color::linear_rgb(0.0, 0.0, 1.0)),
matl(Color::linear_rgb(0.0, 1.0, 0.0)),
matl(Color::linear_rgb(1.0, 0.0, 1.0)),
matl(Color::linear_rgb(0.5, 0.5, 0.0)),
matl(Color::linear_rgb(1.0, 0.5, 0.0)),
];
for i in 0..N_CARS {
let color = colors[i % colors.len()].clone();
commands
.spawn((
Mesh3d(box_mesh.clone()),
MeshMaterial3d(color.clone()),
Transform::from_scale(Vec3::splat(0.5)),
Moves(i as f32 * 2.0),
))
.insert_if(CameraTracked, || i == 0)
.with_children(|parent| {
parent.spawn((
Mesh3d(box_mesh.clone()),
MeshMaterial3d(color),
Transform::from_xyz(0.0, 0.08, 0.03).with_scale(Vec3::new(1.0, 1.0, 0.5)),
));
let mut spawn_wheel = |x: f32, z: f32| {
parent.spawn((
Mesh3d(cylinder.clone()),
MeshMaterial3d(wheel_matl.clone()),
Transform::from_xyz(0.14 * x, -0.045, 0.15 * z)
.with_scale(Vec3::new(0.15, 0.04, 0.15))
.with_rotation(Quat::from_rotation_z(std::f32::consts::FRAC_PI_2)),
Rotates,
));
};
spawn_wheel(1.0, 1.0);
spawn_wheel(1.0, -1.0);
spawn_wheel(-1.0, 1.0);
spawn_wheel(-1.0, -1.0);
});
}
}
fn spawn_barriers(
meshes: &mut Assets<Mesh>,
materials: &mut Assets<StandardMaterial>,
commands: &mut Commands,
) {
const N_CONES: usize = 100;
let capsule = meshes.add(Capsule3d::default());
let matl = materials.add(StandardMaterial {
base_color: Color::srgb_u8(255, 87, 51),
reflectance: 1.0,
..default()
});
let mut spawn_with_offset = |offset: f32| {
for i in 0..N_CONES {
let pos = race_track_pos(
offset,
(i as f32) / (N_CONES as f32) * std::f32::consts::PI * 2.0,
);
commands.spawn((
Mesh3d(capsule.clone()),
MeshMaterial3d(matl.clone()),
Transform::from_xyz(pos.x, -0.65, pos.y).with_scale(Vec3::splat(0.07)),
));
}
};
spawn_with_offset(0.04);
spawn_with_offset(-0.04);
}
fn spawn_trees(
meshes: &mut Assets<Mesh>,
materials: &mut Assets<StandardMaterial>,
commands: &mut Commands,
) {
const N_TREES: usize = 30;
let capsule = meshes.add(Capsule3d::default());
let sphere = meshes.add(Sphere::default());
let leaves = materials.add(Color::linear_rgb(0.0, 1.0, 0.0));
let trunk = materials.add(Color::linear_rgb(0.4, 0.2, 0.2));
let mut spawn_with_offset = |offset: f32| {
for i in 0..N_TREES {
let pos = race_track_pos(
offset,
(i as f32) / (N_TREES as f32) * std::f32::consts::PI * 2.0,
);
let [x, z] = pos.into();
commands.spawn((
Mesh3d(sphere.clone()),
MeshMaterial3d(leaves.clone()),
Transform::from_xyz(x, -0.3, z).with_scale(Vec3::splat(0.3)),
));
commands.spawn((
Mesh3d(capsule.clone()),
MeshMaterial3d(trunk.clone()),
Transform::from_xyz(x, -0.5, z).with_scale(Vec3::new(0.05, 0.3, 0.05)),
));
}
};
spawn_with_offset(0.07);
spawn_with_offset(-0.07);
}
fn setup_ui(mut commands: Commands) {
commands
.spawn((
Text::default(),
Node {
position_type: PositionType::Absolute,
top: Val::Px(12.0),
left: Val::Px(12.0),
..default()
},
))
.with_children(|p| {
p.spawn(TextSpan::default());
p.spawn(TextSpan::default());
p.spawn(TextSpan::new("1/2: -/+ shutter angle (blur amount)\n"));
p.spawn(TextSpan::new("3/4: -/+ sample count (blur quality)\n"));
p.spawn(TextSpan::new("Spacebar: cycle camera\n"));
});
}
fn keyboard_inputs(
mut motion_blur: Single<&mut MotionBlur>,
presses: Res<ButtonInput<KeyCode>>,
text: Single<Entity, With<Text>>,
mut writer: TextUiWriter,
mut camera: ResMut<CameraMode>,
) {
if presses.just_pressed(KeyCode::Digit1) {
motion_blur.shutter_angle -= 0.25;
} else if presses.just_pressed(KeyCode::Digit2) {
motion_blur.shutter_angle += 0.25;
} else if presses.just_pressed(KeyCode::Digit3) {
motion_blur.samples = motion_blur.samples.saturating_sub(1);
} else if presses.just_pressed(KeyCode::Digit4) {
motion_blur.samples += 1;
} else if presses.just_pressed(KeyCode::Space) {
*camera = match *camera {
CameraMode::Track => CameraMode::Chase,
CameraMode::Chase => CameraMode::Track,
};
}
motion_blur.shutter_angle = motion_blur.shutter_angle.clamp(0.0, 1.0);
motion_blur.samples = motion_blur.samples.clamp(0, 64);
let entity = *text;
*writer.text(entity, 1) = format!("Shutter angle: {:.2}\n", motion_blur.shutter_angle);
*writer.text(entity, 2) = format!("Samples: {:.5}\n", motion_blur.samples);
}
/// Parametric function for a looping race track. `offset` will return the point offset
/// perpendicular to the track at the given point.
fn race_track_pos(offset: f32, t: f32) -> Vec2 {
let x_tweak = 2.0;
let y_tweak = 3.0;
let scale = 8.0;
let x0 = ops::sin(x_tweak * t);
let y0 = ops::cos(y_tweak * t);
let dx = x_tweak * ops::cos(x_tweak * t);
let dy = y_tweak * -ops::sin(y_tweak * t);
let dl = ops::hypot(dx, dy);
let x = x0 + offset * dy / dl;
let y = y0 - offset * dx / dl;
Vec2::new(x, y) * scale
}
fn move_cars(
time: Res<Time>,
mut movables: Query<(&mut Transform, &Moves, &Children)>,
mut spins: Query<&mut Transform, (Without<Moves>, With<Rotates>)>,
) {
for (mut transform, moves, children) in &mut movables {
let time = time.elapsed_secs() * 0.25;
let t = time + 0.5 * moves.0;
let dx = ops::cos(t);
let dz = -ops::sin(3.0 * t);
let speed_variation = (dx * dx + dz * dz).sqrt() * 0.15;
let t = t + speed_variation;
let prev = transform.translation;
transform.translation.x = race_track_pos(0.0, t).x;
transform.translation.z = race_track_pos(0.0, t).y;
transform.translation.y = -0.59;
let delta = transform.translation - prev;
transform.look_to(delta, Vec3::Y);
for child in children.iter() {
let Ok(mut wheel) = spins.get_mut(child) else {
continue;
};
let radius = wheel.scale.x;
let circumference = 2.0 * std::f32::consts::PI * radius;
let angle = delta.length() / circumference * std::f32::consts::PI * 2.0;
wheel.rotate_local_y(angle);
}
}
}
fn move_camera(
camera: Single<(&mut Transform, &mut Projection), Without<CameraTracked>>,
tracked: Single<&Transform, With<CameraTracked>>,
mode: Res<CameraMode>,
) {
let (mut transform, mut projection) = camera.into_inner();
match *mode {
CameraMode::Track => {
transform.look_at(tracked.translation, Vec3::Y);
transform.translation = Vec3::new(15.0, -0.5, 0.0);
if let Projection::Perspective(perspective) = &mut *projection {
perspective.fov = 0.05;
}
}
CameraMode::Chase => {
transform.translation =
tracked.translation + Vec3::new(0.0, 0.15, 0.0) + tracked.back() * 0.6;
transform.look_to(tracked.forward(), Vec3::Y);
if let Projection::Perspective(perspective) = &mut *projection {
perspective.fov = 1.0;
}
}
}
}
fn uv_debug_texture() -> Image {
use bevy::render::{render_asset::RenderAssetUsages, render_resource::*};
const TEXTURE_SIZE: usize = 7;
let mut palette = [
164, 164, 164, 255, 168, 168, 168, 255, 153, 153, 153, 255, 139, 139, 139, 255, 153, 153,
153, 255, 177, 177, 177, 255, 159, 159, 159, 255,
];
let mut texture_data = [0; TEXTURE_SIZE * TEXTURE_SIZE * 4];
for y in 0..TEXTURE_SIZE {
let offset = TEXTURE_SIZE * y * 4;
texture_data[offset..(offset + TEXTURE_SIZE * 4)].copy_from_slice(&palette);
palette.rotate_right(12);
}
let mut img = Image::new_fill(
Extent3d {
width: TEXTURE_SIZE as u32,
height: TEXTURE_SIZE as u32,
depth_or_array_layers: 1,
},
TextureDimension::D2,
&texture_data,
TextureFormat::Rgba8UnormSrgb,
RenderAssetUsages::RENDER_WORLD,
);
img.sampler = ImageSampler::Descriptor(ImageSamplerDescriptor {
address_mode_u: ImageAddressMode::Repeat,
address_mode_v: ImageAddressMode::MirrorRepeat,
mag_filter: ImageFilterMode::Nearest,
..ImageSamplerDescriptor::linear()
});
img
}
Reference in New Issue View Git Blame Copy Permalink