background stuff

src/engine.rs

@@ -195,6 +195,14 @@ impl<'context, 'game> Context<'context, 'game> {
         self.entities.push(Entity(id, components));
     }
 
+    pub fn despawn(&mut self, entity_id: u64) {
+        *self.entities = self
+            .entities
+            .drain(..)
+            .filter(|v| v.0 != entity_id)
+            .collect();
+    }
+
     pub fn add_system(&mut self, system: Rc<dyn System>) {
         system.on_add(self);
         self.systems.push(system)

src/main.rs

@@ -46,6 +46,39 @@ impl System for GravitySystem {
     }
 }
 
+#[derive(Component)]
+struct Cloud;
+
+struct CloudSystem;
+
+impl System for CloudSystem {
+    fn on_update(&self, ctx: &mut engine::Context, delta: f64) -> Result<(), engine::Error> {
+        let cloud_amount = ctx.entities_with_component::<Cloud>().len();
+        if cloud_amount < 1 {
+            let cloud = ctx.load_sprite("textures/clouds.png").unwrap();
+            ctx.spawn(vec![
+                Box::new(Cloud),
+                Box::new(Sprite { sprite: cloud }),
+                Box::new(Position(-100.0, 150.0)),
+                Box::new(Velocity(0.0, 0.0)),
+            ]);
+        }
+
+        for id in engine::Quwi::<(Cloud, Velocity)>::new().run(&ctx) {
+            let Velocity(x, _) = ctx.entity_component::<Velocity>(id);
+            *x = if *x < 200.0 { *x + 200.0 * delta } else { *x };
+        }
+
+        for id in engine::Quwi::<(Cloud, Position)>::new().run(&ctx) {
+            let Position(x, _) = ctx.entity_component::<Position>(id);
+            if *x > 1400.0 {
+                ctx.despawn(id);
+            }
+        }
+        Ok(())
+    }
+}
+
 struct SpriteRenderer;
 impl System for SpriteRenderer {
     fn on_update(&self, ctx: &mut engine::Context, _delta: f64) -> Result<(), engine::Error> {
@@ -89,9 +122,17 @@ fn main() {
     context.add_system(Rc::new(SpriteRenderer));
     context.add_system(Rc::new(GravitySystem));
     context.add_system(Rc::new(PlayerMovementSystem));
-    let sprite = context.load_sprite("textures/player.png").unwrap();
+    context.add_system(Rc::new(CloudSystem));
+    let player = context.load_sprite("textures/player.png").unwrap();
+    let background = context.load_sprite("textures/mountains.png").unwrap();
+
     context.spawn(vec![
-        Box::new(Sprite { sprite }),
+        Box::new(Sprite { sprite: background }),
+        Box::new(Position(0.0, 0.0)),
+    ]);
+
+    context.spawn(vec![
+        Box::new(Sprite { sprite: player }),
         Box::new(Position(16.0, 500.0)),
         Box::new(Velocity(0.0, -600.0)),
         Box::new(Gravity),