mirror of
https://github.com/bevyengine/bevy
synced 2024-12-02 01:19:12 +00:00
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.
98 lines
3.4 KiB
Rust
98 lines
3.4 KiB
Rust
//! Illustrates how to scale an object in each direction.
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use std::f32::consts::PI;
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use bevy::prelude::*;
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// Define a component to keep information for the scaled object.
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#[derive(Component)]
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struct Scaling {
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scale_direction: Vec3,
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scale_speed: f32,
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max_element_size: f32,
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min_element_size: f32,
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}
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// Implement a simple initialization.
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impl Scaling {
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fn new() -> Self {
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Scaling {
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scale_direction: Vec3::X,
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scale_speed: 2.0,
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max_element_size: 5.0,
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min_element_size: 1.0,
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}
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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)
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.add_systems(Update, (change_scale_direction, scale_cube))
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.run();
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}
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// Startup system to setup the scene and spawn all relevant entities.
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fn setup(
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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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// Spawn a cube to scale.
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commands.spawn((
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PbrBundle {
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mesh: meshes.add(shape::Cube { size: 1.0 }),
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material: materials.add(Color::WHITE),
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transform: Transform::from_rotation(Quat::from_rotation_y(PI / 4.0)),
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..default()
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},
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Scaling::new(),
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));
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// Spawn a camera looking at the entities to show what's happening in this example.
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commands.spawn(Camera3dBundle {
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transform: Transform::from_xyz(0.0, 10.0, 20.0).looking_at(Vec3::ZERO, Vec3::Y),
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..default()
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});
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// Add a light source for better 3d visibility.
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commands.spawn(PointLightBundle {
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transform: Transform::from_translation(Vec3::ONE * 3.0),
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..default()
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});
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}
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// This system will check if a scaled entity went above or below the entities scaling bounds
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// and change the direction of the scaling vector.
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fn change_scale_direction(mut cubes: Query<(&mut Transform, &mut Scaling)>) {
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for (mut transform, mut cube) in &mut cubes {
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// If an entity scaled beyond the maximum of its size in any dimension
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// the scaling vector is flipped so the scaling is gradually reverted.
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// Additionally, to ensure the condition does not trigger again we floor the elements to
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// their next full value, which should be max_element_size at max.
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if transform.scale.max_element() > cube.max_element_size {
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cube.scale_direction *= -1.0;
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transform.scale = transform.scale.floor();
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}
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// If an entity scaled beyond the minimum of its size in any dimension
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// the scaling vector is also flipped.
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// Additionally the Values are ceiled to be min_element_size at least
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// and the scale direction is flipped.
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// This way the entity will change the dimension in which it is scaled any time it
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// reaches its min_element_size.
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if transform.scale.min_element() < cube.min_element_size {
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cube.scale_direction *= -1.0;
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transform.scale = transform.scale.ceil();
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cube.scale_direction = cube.scale_direction.zxy();
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}
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}
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}
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// This system will scale any entity with assigned Scaling in each direction
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// by cycling through the directions to scale.
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fn scale_cube(mut cubes: Query<(&mut Transform, &Scaling)>, timer: Res<Time>) {
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for (mut transform, cube) in &mut cubes {
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transform.scale += cube.scale_direction * cube.scale_speed * timer.delta_seconds();
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}
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}
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