import SpriteKit

class GameScene: SKScene {

// lastを用意しておく
var last:CFTimeInterval!

override func didMoveToView(view: SKView) {}

override func touchesBegan(touches: NSSet, withEvent event: UIEvent) {}

// 赤い四角を、画面中央から上に向かって打ち出すメソッド
func shoot() {
    let square = SKSpriteNode(color: UIColor.redColor(), size: CGSizeMake(40, 40))
    square.position = CGPoint(x: CGRectGetMidX(self.frame), y: CGRectGetMidY(self.frame))
    square.physicsBody = SKPhysicsBody(rectangleOfSize: CGSizeMake(40, 40))
    square.physicsBody.affectedByGravity = false
    square.physicsBody.velocity = CGVectorMake(0, 100)
    square.physicsBody.linearDamping = false
    self.addChild(square)
}

override func update(currentTime: CFTimeInterval) {

    // lastが未定義ならば、今の時間を入れる。
    if !last {
        last = currentTime
    }

    // 1秒おきに行う処理をかく。
    if last + 1 <= currentTime {

        self.shoot()

        last = currentTime
    }
}
}