Smooth doodling with coalesced touches

.swift

override public func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
  guard let touch = touches.first else {
    return
  }
        
  UIGraphicsBeginImageContextWithOptions(bounds.size, false, 0.0)
  let context = UIGraphicsGetCurrentContext()
        
  image?.draw(in: bounds)
  var touches = [UITouch]()
        
  if let coalescedTouches = event?.coalescedTouches(for: touch) {
    touches = coalescedTouches
  } else {
    touches.append(touch)
  }

  for touch in touches {
    drawStroke(context: context, touch: touch)
  }
        
  image = UIGraphicsGetImageFromCurrentImageContext()
  UIGraphicsEndImageContext()
}