refactor: Dependency Injection to PhysicsEngine2Ds

Engine.Physics2D/PhysicsEngine2D.cs

@@ -12,8 +12,9 @@ public class PhysicsEngine2D : IPhysicsEngine2D
     private readonly List<ICollider2D> colliders = new(64);
 
     private int _iterationCount = 1;
-    private ICollisionDetector2D collisionDetector = new CollisionDetector2D();
-    private ICollisionResolver2D collisionResolver = new CollisionResolver2D();
+
+    private readonly ICollisionDetector2D collisionDetector = null!;
+    private readonly ICollisionResolver2D collisionResolver = null!;
 
     public int IterationCount { get => _iterationCount; set => _iterationCount = value < 1 ? 1 : value; }
 
@@ -122,4 +123,16 @@ public class PhysicsEngine2D : IPhysicsEngine2D
 
         colliders.Remove(collider2D);
     }
+
+    public PhysicsEngine2D()
+    {
+        collisionDetector = new CollisionDetector2D();
+        collisionResolver = new CollisionResolver2D();
+    }
+
+    public PhysicsEngine2D(ICollisionDetector2D collisionDetector, ICollisionResolver2D collisionResolver)
+    {
+        this.collisionDetector = collisionDetector;
+        this.collisionResolver = collisionResolver;
+    }
 }