Vendor dependencies for 0.3.0 release

vendor/bevy/examples/ecs/system_param.rs

@@ -0,0 +1,47 @@
+//! This example creates a custom [`SystemParam`] struct that counts the number of players.
+
+use bevy::{ecs::system::SystemParam, prelude::*};
+
+fn main() {
+    App::new()
+        .insert_resource(PlayerCount(0))
+        .add_systems(Startup, spawn)
+        .add_systems(Update, count_players)
+        .run();
+}
+
+#[derive(Component)]
+struct Player;
+
+#[derive(Resource)]
+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)]
+struct PlayerCounter<'w, 's> {
+    players: Query<'w, 's, &'static Player>,
+    count: ResMut<'w, PlayerCount>,
+}
+
+impl<'w, 's> PlayerCounter<'w, 's> {
+    fn count(&mut self) {
+        self.count.0 = self.players.iter().len();
+    }
+}
+
+/// Spawn some players to count
+fn spawn(mut commands: 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);
+}