000dd4c1c2
It took me a little while to figure out how to use the `SystemParam` derive macro to easily create my own params. So I figured I'd add some docs and an example with what I learned. - Fixed a bug in the `SystemParam` derive macro where it didn't detect the correct crate name when used in an example (no longer relevant, replaced by #1426 - see further) - Added some doc comments and a short example code block in the docs for the `SystemParam` trait - Added a more complete example with explanatory comments in examples
44 lines
1.1 KiB
Rust
44 lines
1.1 KiB
Rust
use bevy::{ecs::SystemParam, prelude::*};
|
|
|
|
/// This example creates a SystemParam struct that counts the number of players
|
|
fn main() {
|
|
App::build()
|
|
.insert_resource(PlayerCount(0))
|
|
.add_startup_system(spawn.system())
|
|
.add_system(count_players.system())
|
|
.run();
|
|
}
|
|
|
|
struct Player;
|
|
struct PlayerCount(usize);
|
|
|
|
/// The SystemParam struct can contain any types that can also be included in a
|
|
/// system function signature.
|
|
///
|
|
/// In this example, it includes a query and a mutable resource.
|
|
#[derive(SystemParam)]
|
|
pub struct PlayerCounter<'a> {
|
|
players: Query<'a, &'a Player>,
|
|
count: ResMut<'a, PlayerCount>,
|
|
}
|
|
|
|
impl<'a> PlayerCounter<'a> {
|
|
fn count(&mut self) {
|
|
self.count.0 = self.players.iter().len();
|
|
}
|
|
}
|
|
|
|
/// Spawn some players to count
|
|
fn spawn(commands: &mut Commands) {
|
|
commands.spawn((Player,));
|
|
commands.spawn((Player,));
|
|
commands.spawn((Player,));
|
|
}
|
|
|
|
/// The SystemParam can be used directly in a system argument.
|
|
fn count_players(mut counter: PlayerCounter) {
|
|
counter.count();
|
|
|
|
println!("{} players in the game", counter.count.0);
|
|
}
|