Implement ant random walk

src/systems/mod.rs

@@ -0,0 +1,2 @@
+pub mod random_walk;
+pub mod startup;

src/systems/random_walk.rs

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+use crate::{
+    components::common::{Position, RandomizedVelocity},
+    ANT_SPEED, MAX_POSITION, MIN_POSITION, RANDOM_WALK_CONE,
+};
+use bevy::{math::VectorSpace, prelude::*};
+
+/// Randomizes the ``RandomizedVelocity`` components of entities that have them.
+#[allow(clippy::needless_pass_by_value)] // I can't specify &Res<Time>, so pass by value
+pub fn randomized_velocity_system(mut query: Query<&mut RandomizedVelocity>) {
+    for mut velocity in &mut query {
+        let mut new_velocity: Vec2 = Vec2::from_angle(
+            // We first multiply with CONE to get the angle-delta to [0, CONE].
+            // Then, we subtract CONE/2 to bring the angle-delta to [-CONE/2, CONE/2].
+            // Lastly, we add the angle-delta to the current angle.
+            // This should vary the direction in a front-facing CONE-degree cone.
+            rand::random::<f32>().mul_add(
+                RANDOM_WALK_CONE,
+                velocity.0.to_angle() - RANDOM_WALK_CONE / 2.,
+            ),
+        );
+        new_velocity = new_velocity.normalize() * ANT_SPEED;
+
+        velocity.0 = new_velocity;
+    }
+}
+
+/// Updates ``Position`` and ``Transform`` components of entities that also have
+/// the ``RandomizedVelocity`` component, like an ``Ant``.
+#[allow(clippy::module_name_repetitions)]
+pub fn random_walk_system(
+    // We query for each entity that has a Position, Transform and Velocity component.
+    // The Transform component comes from the SpriteBundle.
+    mut query: Query<(&mut Position, &mut Transform, &RandomizedVelocity)>,
+) {
+    for (mut position, mut transform, velocity) in &mut query {
+        let new_position: Vec2 = position.0 + velocity.0;
+
+        transform.translation = new_position.clamp(MIN_POSITION, MAX_POSITION).extend(0.);
+        position.0 = new_position.clamp(MIN_POSITION, MAX_POSITION);
+    }
+}
+
+/// Sets an ant's velocity perpendicular to a wall, if touched.
+pub fn wall_avoidance_system(mut query: Query<(&Position, &mut RandomizedVelocity)>) {
+    let touches_left_wall = |position: Vec2| -> bool { position.x <= 0. };
+    let touches_right_wall = |position: Vec2| -> bool { position.x >= MAX_POSITION.x };
+    let touches_bottom_wall = |position: Vec2| -> bool { position.y <= 0. };
+    let touches_top_wall = |position: Vec2| -> bool { position.y >= MAX_POSITION.y };
+
+    for (position, mut velocity) in &mut query {
+        let mut new_velocity: Vec2 = velocity.0;
+
+        if touches_left_wall(position.0) {
+            new_velocity = Vec2::new(1., 0.);
+        } else if touches_right_wall(position.0) {
+            new_velocity = Vec2::new(-1., 0.);
+        } else if touches_bottom_wall(position.0) {
+            new_velocity = Vec2::new(0., 1.);
+        } else if touches_top_wall(position.0) {
+            new_velocity = Vec2::new(0., -1.);
+        }
+
+        velocity.0 = new_velocity;
+    }
+}

src/systems/startup.rs

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+use crate::{components::ant::AntBundle, ANT_COUNT};
+use bevy::prelude::*;
+
+/// Signal that the app has started by printing a message to the terminal.
+pub fn hello_ants_system() {
+    println!("Hello, fellow 🐜");
+}
+
+/// Prepares the environment before the Update schedule by spawning required entities.
+pub fn setup_system(mut commands: Commands) {
+    // Using the default camera, world space coordinates correspond 1:1 with screen pixels.
+    // The point (0, 0) is in the center of the screen.
+    commands.spawn(Camera2dBundle::default());
+
+    // Spawn cute ants
+    for _ in 0..ANT_COUNT {
+        commands.spawn(AntBundle::new(Vec2::new(0., 0.), Color::srgb(1., 0., 0.)));
+    }
+    println!("Spawned {ANT_COUNT} cute ants 😍");
+}