Better particle systems example

Makefile

@@ -5,8 +5,8 @@
 # EXAMPLE=post_processing
 # EXAMPLE=shapes
 # EXAMPLE=ecs_sprite
-EXAMPLE=ecs_topdown_game
-# EXAMPLE=particle_systems
+# EXAMPLE=ecs_topdown_game
+EXAMPLE=particle_systems
 
 # default: build-examples
 # default: wasm-build

README.md

@@ -344,7 +344,7 @@ comfy is free and open source and dual licensed under MIT and Apache 2.0 license
 - [ ] lighting example
 - [ ] combat text example
 - [ ] font loading
-- [ ] particle systems
+- [x] particle systems
 - [x] text
 - [ ] blood canvas
 - [ ] raytracing

comfy/examples/particle_systems.rs

@@ -3,15 +3,54 @@ use comfy::*;
 simple_game!("Particle Systems Example", setup, update);
 
 fn setup(c: &mut EngineContext) {
+    c.load_texture_from_bytes(
+        // Every texture gets a string name later used to reference it.
+        "comfy",
+        include_bytes!(concat!(
+            env!("CARGO_MANIFEST_DIR"),
+            "/../assets/comfy.png"
+        )),
+        wgpu::AddressMode::ClampToEdge,
+    );
+
+    // ParticleSystem's are based off the same principle as singular Particle's, except the
+    // automatically handle the spawning.
+
     c.commands().spawn((
-        ParticleSystem::with_spawn_rate(100, 0.1, || {
+        ParticleSystem::with_spawn_rate(500, 0.01, || {
             Particle {
+                texture: texture_id("comfy"),
                 position: random_circle(5.0),
                 size: splat(1.0),
+                // Other than the builtin easing curves, any f32 -> f32 curve
+                // will work.
+                size_curve: quad_in_out,
+
+                direction: vec2(0.0, 1.0),
+                velocity: 10.0,
+                velocity_end: 5.0,
+                ..Default::default()
+            }
+        })
+        .with_size(vec2(3.0, 8.0)),
+        Transform::position(vec2(-5.0, 0.0)),
+    ));
+
+    c.commands().spawn((
+        ParticleSystem::with_spawn_on_death(300, || {
+            Particle {
+                texture: texture_id("comfy"),
+                position: random_circle(5.0),
+                size: splat(0.5),
+                size_curve: expo_out,
+                // Both size and color can be faded.
+                fade_type: FadeType::Both,
+                color_start: RED,
+                color_end: RED,
                 ..Default::default()
             }
         }),
-        Transform::position(Vec2::ZERO),
+        Transform::position(vec2(5.0, 0.0)),
     ));
 }
 

comfy/src/particles.rs

@@ -49,6 +49,9 @@ impl ParticleSystem {
         }
     }
 
+    /// Creates a particle system that always maintains a `max_particles` number of live particles.
+    /// Every time a particle's lifetime ends, a new particle is immediately spawned to maintain a
+    /// constant number.
     pub fn with_spawn_on_death(
         max_particles: usize,
         particle_builder: impl Fn() -> Particle + Send + Sync + 'static,