Border avoidance system

src/birdoids_plugin.rs

@@ -3,6 +3,7 @@ use bevy::{prelude::*, sprite::MaterialMesh2dBundle};
 
 const BACKGROUND_COLOR: Color = Color::srgb(0.4, 0.4, 0.4);
 const PLAYERBOID_COLOR: Color = Color::srgb(1.0, 0.0, 0.0);
+const TURN_FACTOR: f32 = 1.;
 
 pub struct BoidsPlugin;
 
@@ -13,6 +14,7 @@ impl Plugin for BoidsPlugin{
             .add_systems(Startup, (spawn_camera, spawn_boids))
             .add_systems(FixedUpdate, (
                 apply_velocity,
+                turn_if_edge,
                 check_keyboard,
             ));
     }
@@ -82,6 +84,31 @@ fn spawn_boids(
     ));
 }
 
+fn turn_if_edge(
+    mut query: Query<(&mut Transform, &mut Velocity), With<Boid>>,
+    window: Query<&Window>,
+) {
+    if let Ok(window) = window.get_single() {
+        let (width, height) = (window.resolution.width(), window.resolution.height());
+        for (transform, mut velocity) in &mut query {
+            let boid_pos = transform.translation.xy();
+            if boid_pos.x <= -width / 2. + 50. {
+                velocity.x += TURN_FACTOR;
+            } else if boid_pos.x >= width / 2. - 50. {
+                velocity.x -= TURN_FACTOR;
+            }
+
+            if boid_pos.y <= -height / 2. + 50. {
+                velocity.y += TURN_FACTOR;
+            } else if boid_pos.y >= height / 2. - 50. {
+                velocity.y -= TURN_FACTOR;
+            }
+        }
+    } else {
+        panic!("System turn_if_edge(...) got an Err(_) when getting the window properties");
+    }
+}
+
 fn apply_velocity(mut query: Query<(&mut Transform, &Velocity)>, time: Res<Time>) {
     for (mut transform, velocity) in &mut query {
         let delta_position = **velocity * time.delta_seconds();