Implement a proper gun fire-rate mechanism

There is now a `Weapon` component which is just a timer for the gun's
fire rate. It is ticked every frame, clamping at the "ready" state (0
time remaining).

The ship spawns with this thing, and the `input_ship_shoot` system has
been updated to use it.

src/config.rs

@@ -13,6 +13,7 @@ pub(crate) const BACKGROUND_COLOR: Color = Color::srgb(0.3, 0.3, 0.3);
 pub(crate) const PLAYER_SHIP_COLOR: Color = Color::srgb(1.0, 1.0, 1.0);
 pub(crate) const SHIP_THRUSTER_COLOR_ACTIVE: Color = Color::srgb(1.0, 0.2, 0.2);
 pub(crate) const SHIP_THRUSTER_COLOR_INACTIVE: Color = Color::srgb(0.5, 0.5, 0.5);
+pub(crate) const SHIP_FIRE_RATE: f32 = 3.0; // in bullets-per-second
 pub(crate) const ASTEROID_SMALL_COLOR: Color = Color::srgb(1.0, 0., 0.);
 pub(crate) const BULLET_COLOR: Color = Color::srgb(0.0, 0.1, 0.9);
 // TODO: asteroid medium & large

src/lib.rs

@@ -16,7 +16,7 @@ use crate::config::{
     SHIP_THRUSTER_COLOR_INACTIVE,
 };
 use crate::machinery::AsteroidSpawner;
-use crate::objects::{Bullet, Ship};
+use crate::objects::{Bullet, Ship, Weapon};
 use crate::physics::AngularVelocity;
 
 use bevy::prelude::*;
@@ -160,19 +160,25 @@ fn input_ship_rotation(
 /// tick those timers. Maybe this system?
 fn input_ship_shoot(
     keyboard_input: Res<ButtonInput<KeyCode>>,
-    ship: Single<(&Transform, &physics::Velocity), With<Ship>>,
+    ship: Single<(&Transform, &physics::Velocity, &mut Weapon), With<Ship>>,
     game_assets: Res<GameAssets>,
     mut commands: Commands,
+    time: Res<Time>,
 ) {
-    let (ship_pos, ship_vel) = *ship;
+    let (ship_pos, ship_vel, mut weapon) = ship.into_inner();
 
-    // Derive bullet velocity, add to the ship's velocity
-    let bullet_vel = (ship_pos.rotation * Vec3::X).xy() * BULLET_SPEED;
-    let bullet_vel = bullet_vel + ship_vel.0;
+    // Tick the timer so the cooldown eventually finishes. Once it does, the
+    // value will clamp at 0. The weapon is now ready.
+    weapon.tick(time.delta());
+
+    // If the weapon is ready and the player presses the trigger,
+    // spawn a bullet & reset the timer.
+    if weapon.finished() && keyboard_input.pressed(KeyCode::Space) {
+        weapon.reset();
+        // Derive bullet velocity, add to the ship's velocity
+        let bullet_vel = (ship_pos.rotation * Vec3::X).xy() * BULLET_SPEED;
+        let bullet_vel = bullet_vel + ship_vel.0;
 
-    // TODO: create a timer for the gun fire rate.
-    // For now, spawn one for each press of the spacebar.
-    if keyboard_input.just_pressed(KeyCode::Space) {
         commands.spawn((
             Bullet,
             Collider::ball(0.2),

src/objects.rs

@@ -22,7 +22,7 @@ use bevy_rapier2d::prelude::{ActiveCollisionTypes, ActiveEvents, Collider, Senso
 
 use crate::{
     AngularVelocity, GameAssets, GameState, Lives,
-    config::ASTEROID_LIFETIME,
+    config::{ASTEROID_LIFETIME, SHIP_FIRE_RATE},
     events::{AsteroidDestroy, BulletDestroy, ShipDestroy, SpawnAsteroid},
     machinery::Lifetime,
     physics::{Velocity, Wrapping},
@@ -55,6 +55,10 @@ impl AsteroidSize {
 #[derive(Component)]
 pub struct Ship;
 
+/// The ship's gun (is just a timer)
+#[derive(Component, Deref, DerefMut)]
+pub struct Weapon(Timer);
+
 /// Marker component for bullets.
 #[derive(Component)]
 pub struct Bullet;
@@ -144,6 +148,7 @@ pub fn spawn_player(mut commands: Commands, game_assets: Res<GameAssets>) {
             ActiveEvents::COLLISION_EVENTS,
             ActiveCollisionTypes::STATIC_STATIC,
             Ship,
+            Weapon(Timer::from_seconds(1.0 / SHIP_FIRE_RATE, TimerMode::Once)),
             Wrapping,
             Velocity(Vec2::ZERO),
             AngularVelocity(0.0),