mirror of
https://github.com/bevyengine/bevy
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a795de30b4
# Motivation
When spawning entities into a scene, it is very common to create assets
like meshes and materials and to add them via asset handles. A common
setup might look like this:
```rust
fn setup(
mut commands: Commands,
mut meshes: ResMut<Assets<Mesh>>,
mut materials: ResMut<Assets<StandardMaterial>>,
) {
commands.spawn(PbrBundle {
mesh: meshes.add(Mesh::from(shape::Cube { size: 1.0 })),
material: materials.add(StandardMaterial::from(Color::RED)),
..default()
});
}
```
Let's take a closer look at the part that adds the assets using `add`.
```rust
mesh: meshes.add(Mesh::from(shape::Cube { size: 1.0 })),
material: materials.add(StandardMaterial::from(Color::RED)),
```
Here, "mesh" and "material" are both repeated three times. It's very
explicit, but I find it to be a bit verbose. In addition to being more
code to read and write, the extra characters can sometimes also lead to
the code being formatted to span multiple lines even though the core
task, adding e.g. a primitive mesh, is extremely simple.
A way to address this is by using `.into()`:
```rust
mesh: meshes.add(shape::Cube { size: 1.0 }.into()),
material: materials.add(Color::RED.into()),
```
This is fine, but from the names and the type of `meshes`, we already
know what the type should be. It's very clear that `Cube` should be
turned into a `Mesh` because of the context it's used in. `.into()` is
just seven characters, but it's so common that it quickly adds up and
gets annoying.
It would be nice if you could skip all of the conversion and let Bevy
handle it for you:
```rust
mesh: meshes.add(shape::Cube { size: 1.0 }),
material: materials.add(Color::RED),
```
# Objective
Make adding assets more ergonomic by making `Assets::add` take an `impl
Into<A>` instead of `A`.
## Solution
`Assets::add` now takes an `impl Into<A>` instead of `A`, so e.g. this
works:
```rust
commands.spawn(PbrBundle {
mesh: meshes.add(shape::Cube { size: 1.0 }),
material: materials.add(Color::RED),
..default()
});
```
I also changed all examples to use this API, which increases consistency
as well because `Mesh::from` and `into` were being used arbitrarily even
in the same file. This also gets rid of some lines of code because
formatting is nicer.
---
## Changelog
- `Assets::add` now takes an `impl Into<A>` instead of `A`
- Examples don't use `T::from(K)` or `K.into()` when adding assets
## Migration Guide
Some `into` calls that worked previously might now be broken because of
the new trait bounds. You need to either remove `into` or perform the
conversion explicitly with `from`:
```rust
// Doesn't compile
let mesh_handle = meshes.add(shape::Cube { size: 1.0 }.into()),
// These compile
let mesh_handle = meshes.add(shape::Cube { size: 1.0 }),
let mesh_handle = meshes.add(Mesh::from(shape::Cube { size: 1.0 })),
```
## Concerns
I believe the primary concerns might be:
1. Is this too implicit?
2. Does this increase codegen bloat?
Previously, the two APIs were using `into` or `from`, and now it's
"nothing" or `from`. You could argue that `into` is slightly more
explicit than "nothing" in cases like the earlier examples where a
`Color` gets converted to e.g. a `StandardMaterial`, but I personally
don't think `into` adds much value even in this case, and you could
still see the actual type from the asset type.
As for codegen bloat, I doubt it adds that much, but I'm not very
familiar with the details of codegen. I personally value the user-facing
code reduction and ergonomics improvements that these changes would
provide, but it might be worth checking the other effects in more
detail.
Another slight concern is migration pain; apps might have a ton of
`into` calls that would need to be removed, and it did take me a while
to do so for Bevy itself (maybe around 20-40 minutes). However, I think
the fact that there *are* so many `into` calls just highlights that the
API could be made nicer, and I'd gladly migrate my own projects for it.
120 lines
4 KiB
Markdown
120 lines
4 KiB
Markdown
# B0004
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A runtime warning.
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An [`Entity`] with a hierarchy-inherited component has a [`Parent`]
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without the hierarchy-inherited component in question.
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The hierarchy-inherited components defined in bevy include:
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- [`InheritedVisibility`]
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- [`GlobalTransform`]
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Third party plugins may also define their own hierarchy components, so
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read the warning message carefully and pay attention to the exact type
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of the missing component.
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To fix this warning, add the missing hierarchy component to all ancestors
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of entities with the hierarchy component you wish to use.
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The following code will cause a warning to be emitted:
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```rust,no_run
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use bevy::prelude::*;
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// WARNING: this code is buggy
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fn setup_cube(
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mut commands: Commands,
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mut meshes: ResMut<Assets<Mesh>>,
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mut materials: ResMut<Assets<StandardMaterial>>,
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) {
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commands
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.spawn(TransformBundle::default())
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.with_children(|parent| {
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// cube
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parent.spawn(PbrBundle {
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mesh: meshes.add(shape::Cube { size: 1.0 }),
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material: materials.add(Color::rgb(0.8, 0.7, 0.6)),
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transform: Transform::from_xyz(0.0, 0.5, 0.0),
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..default()
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});
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});
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// camera
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commands.spawn(Camera3dBundle {
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transform: Transform::from_xyz(-2.0, 2.5, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
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..default()
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});
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}
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fn main() {
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App::new()
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.add_plugins(DefaultPlugins)
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.add_systems(Startup, setup_cube)
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.run();
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}
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```
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This code **will not** show a cube on screen.
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This is because the entity spawned with `commands.spawn(…)`
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doesn't have a [`ViewVisibility`] or [`InheritedVisibility`] component.
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Since the cube is spawned as a child of an entity without the
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visibility components, it will not be visible at all.
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To fix this, you must use [`SpatialBundle`] over [`TransformBundle`],
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as follows:
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```rust,no_run
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use bevy::prelude::*;
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fn setup_cube(
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mut commands: Commands,
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mut meshes: ResMut<Assets<Mesh>>,
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mut materials: ResMut<Assets<StandardMaterial>>,
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) {
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commands
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// We use SpatialBundle instead of TransformBundle, it contains the
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// visibility components needed to display the cube,
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// In addition to the Transform and GlobalTransform components.
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.spawn(SpatialBundle::default())
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.with_children(|parent| {
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// cube
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parent.spawn(PbrBundle {
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mesh: meshes.add(shape::Cube { size: 1.0 }),
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material: materials.add(Color::rgb(0.8, 0.7, 0.6)),
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transform: Transform::from_xyz(0.0, 0.5, 0.0),
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..default()
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});
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});
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// camera
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commands.spawn(Camera3dBundle {
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transform: Transform::from_xyz(-2.0, 2.5, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
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..default()
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});
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}
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fn main() {
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App::new()
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.add_plugins(DefaultPlugins)
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.add_systems(Startup, setup_cube)
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.run();
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}
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```
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A similar problem occurs when the [`GlobalTransform`] component is missing.
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However, when a parent [`GlobalTransform`] is missing,
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it will simply prevent all transform propagation,
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including when updating the [`Transform`] component of the child.
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You will most likely encounter this warning when loading a scene
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as a child of a pre-existing [`Entity`] that does not have the proper components.
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[`InheritedVisibility`]: https://docs.rs/bevy/*/bevy/render/view/struct.InheritedVisibility.html
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[`ViewVisibility`]: https://docs.rs/bevy/*/bevy/render/view/struct.ViewVisibility.html
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[`GlobalTransform`]: https://docs.rs/bevy/*/bevy/transform/components/struct.GlobalTransform.html
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[`Transform`]: https://docs.rs/bevy/*/bevy/transform/components/struct.Transform.html
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[`Parent`]: https://docs.rs/bevy/*/bevy/hierarchy/struct.Parent.html
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[`Entity`]: https://docs.rs/bevy/*/bevy/ecs/entity/struct.Entity.html
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[`SpatialBundle`]: https://docs.rs/bevy/*/bevy/render/prelude/struct.SpatialBundle.html
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[`TransformBundle`]: https://docs.rs/bevy/*/bevy/transform/struct.TransformBundle.html
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