Add ParticleSystem::oneshot and example (#57)

Co-authored-by: Abnormal Brain Studios <[email protected]>

examples/oneshot.rs

@@ -0,0 +1,63 @@
+//! This example shows how particle systems can be spawned dynamically and
+//! automatically despawned when finished.
+
+use bevy::{input::common_conditions::input_just_pressed, prelude::*, window::PrimaryWindow};
+use bevy_particle_systems::{
+    ParticleBurst, ParticleSystem, ParticleSystemBundle, ParticleSystemPlugin, Playing,
+    VelocityModifier,
+};
+
+fn main() {
+    App::new()
+        .insert_resource(ClearColor(Color::BLACK))
+        .add_plugins((DefaultPlugins, ParticleSystemPlugin))
+        .add_systems(Startup, setup)
+        .add_systems(
+            Update,
+            spawn_particle_systems.run_if(input_just_pressed(MouseButton::Left)),
+        )
+        .run();
+}
+
+fn setup(mut commands: Commands) {
+    commands.spawn(Camera2dBundle::default());
+}
+
+fn spawn_particle_systems(
+    mut commands: Commands,
+    window: Query<&Window, With<PrimaryWindow>>,
+    camera: Query<(&Camera, &GlobalTransform)>,
+) {
+    let (camera, camera_transform) = camera.single();
+
+    if let Some(world_position) = window
+        .single()
+        .cursor_position()
+        .and_then(|cursor| camera.viewport_to_world(camera_transform, cursor))
+        .map(|ray| ray.origin.truncate())
+    {
+        commands.spawn((
+            ParticleSystemBundle {
+                transform: Transform::from_translation(world_position.extend(0.)),
+                particle_system: ParticleSystem {
+                    spawn_rate_per_second: 0.0.into(),
+                    max_particles: 1_000,
+                    initial_speed: (0.0..300.0).into(),
+                    scale: 2.0.into(),
+                    velocity_modifiers: vec![
+                        VelocityModifier::Drag(0.001.into()),
+                        VelocityModifier::Vector(Vec3::new(0.0, -400.0, 0.0).into()),
+                    ],
+                    color: (Color::BLUE..Color::rgba(1.0, 0.0, 0.0, 0.0)).into(),
+                    bursts: vec![ParticleBurst {
+                        time: 0.0,
+                        count: 1000,
+                    }],
+                    ..ParticleSystem::oneshot()
+                },
+                ..default()
+            },
+            Playing,
+        ));
+    }
+}

src/components.rs

@@ -236,6 +236,19 @@ impl Default for ParticleSystem {
     }
 }
 
+impl ParticleSystem {
+    /// A oneshot particle system, that doesn't loop and despawns when finished
+    ///
+    /// Appropriate base for collision effects etc.
+    pub fn oneshot() -> Self {
+        Self {
+            looping: false,
+            despawn_on_finish: true,
+            ..Default::default()
+        }
+    }
+}
+
 /// An individual Particle, spawned by a [`ParticleSystem`]
 ///
 /// The ``parent_entity`` should link to the entity with the spawning [`ParticleSystem`] on it.