add homing projectiles

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()