public ParticleInstance(Vector2 position, Vector2 velocity, Emitter source)
 {
     this.position = position;
     this.velocity = velocity;
     angle = (float)Math.Atan2(-velocity.Y, velocity.X);
     this.source = source;
     age = 0;
 }
 /// <summary>
 /// Removes an emitter from the graphics object.
 /// </summary>
 /// <param name="obj">The emitter to remove. It should be created from the current instance's CreateEmitter method.</param>
 public void RemoveEmitter(Emitter obj)
 {
     emitters.Remove(obj);
 }
 public ParticleInstance MakeInstance(Vector2 Position, Vector2 Velocity, Emitter Source)
 {
     return new ParticleInstance(Position, Velocity, Source);
 }