add homing projectiles

src/ability.js

@@ -4,7 +4,6 @@ import Projectile from './projectile.js'
 export default class Ability {
   static skillshot({ range, radius, speed, onCollide, after }) {
     return function(x, y) {
-      console.log(this)
       const projectile = new Projectile()
       const destination = this.position.clone().add(new Vector2(x, y).sub(this.position).normalize().multiplyScalar(range))
       projectile.owner = this.id
@@ -17,4 +16,31 @@ export default class Ability {
       this.game?.spawnProjectile(projectile)
     }
   }
+
+  static homingProjectile({ range, radius, speed, onCollide, after }) {
+    return function(x, y) {
+      const cursor = new Vector2(x, y)
+      let closest = null
+      let distance = Infinity
+      this.game?.entities.filter((e) => e.id != this.id && e.position.clone().sub(this.position).length() < range).forEach((e) => {
+        const newDistance = e.position.clone().sub(cursor).length() < distance
+        if (newDistance < distance) {
+          closest = e
+          distance = newDistance
+        }
+      })
+
+      if (closest == null) { return } // TODO: refund
+
+      const projectile = new Projectile()
+      projectile.owner = this.id
+      projectile.position.copy(this.position)
+      projectile.homingTarget = closest
+      projectile.radius = radius
+      projectile.speed = speed
+      projectile.after = after
+      projectile.onCollide = onCollide
+      this.game?.spawnProjectile(projectile)
+    }
+  }
 }

src/entity.js

@@ -12,7 +12,7 @@ export default class Entity {
   health = 1
   maxHealth = 1
   abilities = [
-    () => {},
+    Ability.homingProjectile({ range: 600, radius: 3, speed: 500, onCollide: Effect.damage({ despawn: true }) }),
     Ability.skillshot({ range: 800, radius: 5, speed: 3000, onCollide: Effect.damage({ despawn: true }) }),
     () => {},
     () => {},

src/projectile.js

@@ -13,12 +13,25 @@ export default class Projectile {
 
   #position = new Vector2()
   #dest = null
+  #homingTarget = null
   #game = null
   
   get collider() {
     return new SAT.Circle(new SAT.Vector(this.x, this.y), this.radius)
   }
 
+  get homing() {
+    return !!this.#homingTarget
+  }
+
+  get destination() {
+    return this.#dest ?? this.#homingTarget?.position
+  }
+
+  set homingTarget(value) {
+    this.#homingTarget = value
+  }
+
   constructor(...options) {
     Object.entries(options).forEach((value, key) => this[key] = value)
   }
@@ -43,7 +56,7 @@ export default class Projectile {
   }
 
   checkIfArrived() {
-    if (!this.#position.equals(this.#dest)) { return }
+    if (!this.#position.equals(this.destination)) { return }
 
     if (this.after != null) {
       this.after(this)
@@ -68,7 +81,7 @@ export default class Projectile {
 
   takeStep() {
     const speed = (this.speed / (this.game?.tickBudget ?? 1000))
-    const destination = this.#dest
+    const destination = this.destination
     const difference = destination.clone().sub(this.position)
     const distance = difference.length()
     const direction = difference.clone().normalize()