A simple helper for spawning objects in Bevy.
First, create an enum that holds objects you might want to spawn:
rust
enum Objects {
Player,
Monster,
Coin,
}
Think about which data you want to pass to the spawning function. In this example, we will specify a Transform for the new object.
Next, add the plugin to your app, noting the two types we just mentioned:
```rust,ignore use spew::prelude::; use bevy::prelude::;
fn main() {
App::build()
// ...
.add_plugin(SpewPlugin::
Now, we are ready to register our spawn functions. Each variant of the enum will be associated with its own spawn function that takes in a &mut World and the user provided data:
```rust,ignore
use spew::prelude::;
use bevy::prelude::;
fn main() { App::build() // ... .addspawners( // <--- Register the spawn functions (Objects::Player, spawnplayer), (Objects::Monster, spawnmonster), (Objects::Coin, spawncoin), ) // ... .run(); }
fn spawnplayer(world: &mut World, transform: Transform) { world.spawn(( Name::new("Spiffy the Adventurer"), TransformBundle::fromtransform(transform), )); }
fn spawnmonster(world: &mut World, transform: Transform) { world.spawn(( Name::new("Grumblor the Grumpy"), TransformBundle::fromtransform(transform), )); }
fn spawncoin(world: &mut World, transform: Transform) { world.spawn(( Name::new("$1000"), TransformBundle::fromtransform(transform), )); } ```
Finally, we can set our spawn functions to work by sending a SpawnEvent:
```rust,ignore
use spew::prelude::;
use bevy::prelude::;
fn main() { App::build() // ... .addsystem(setupmap.on_startup()) // ... .run(); }
fn setupmap(mut spawnevents: EventWriter
You can read through the docs or peruse the examples for more use cases. Other cool stuff you can do is delay the spawning by a certain amount of frames or time or organize your spawn lists into multiple enums.
| bevy | spew | |------|------| | 0.10 | 0.1 |
Bevy's Commands API allows you to spawn new entities with arbitrary components:
```rust
use bevy::prelude::*;
fn spawnplayer(commands: &mut Commands) {
commands.spawn((
Name::new("Adventurer"),
TransformBundle::fromtransform(Transform::from_xyz(0.0, 0.0, 0.0)),
));
}
This works great! We can spawn more complex objects by just adding more components like assets:
rust
use std::f32::consts::TAU;
use bevy::prelude::*;
fn spawnbullet(commands: &mut Commands, assetserver: Res
but, in a real project, we would not spawn a bullet like that. The bullet would be spawned by a weapon at a certain translation.
We might thus encapsulate the bullet spawning like this:
rust,ignore
use bevy::prelude::*;
fn handleinput(...) {
// ...
if shouldfirebullet {
let position = playertransform.translation;
spawnbullet(&mut commands, &asset_server, position);
}
}
fn spawnbullet(commands: &mut Commands, assetserver: &AssetServer, position: Vec3) { commands.spawn(( Name::new("Bullet"), SceneBundle { scene: assetserver.load("models/bullet.gltf#Scene0"), transform: Transform { translation: position, scale: Vec3::splat(0.012), rotation: Quat::fromrotation_y(TAU / 2.), }, ..default() }, )); } ```
As you can see, this works but is quite ugly. handle_input has to pass around an asset server we might otherwise not even need in the system,
and spawn_bullet has a jumble of seemingly unrelated parameters that will grow and grow over time. Growing parameter lists are not a problem
when writing a system, but notice how here spawn_bullet is no longer a system but a helper function. Thus, its call will get longer and uglier over time,
with all its parameters leaking into handle_input.
The solution to this is to move the spawning of the bullet into an own system that is accessed indirectly by handle_input via events, which is just what this crate helps you with! :)