Randomizing node movement duration

问题:

I am making a game in SpriteKit and I have a node that is moving back and forth across the screen and repeating using the code:

    let moveRight = SKAction.moveByX(frame.size.width/2.8, y: 0, duration: 1.5)
    let moveLeft = SKAction.moveByX(-frame.size.width/2.8, y: 0, duration: 1.5)
    let texRight = SKAction.setTexture(SKTexture(imageNamed: "Drake2"))
    let texLeft = SKAction.setTexture(SKTexture(imageNamed: "Drake1"))
    let moveBackAndForth = SKAction.repeatActionForever(SKAction.sequence([texRight, moveRight, texLeft, moveLeft,]))
    Drake1.runAction(moveBackAndForth)

I am trying to figure out what method I can use to randomize the duration. Every time moveBackandForth runs, I want it to rerun using a different duration, (within games, not between). If someone could give me some example code to try I would really appreciate it.

Also arc4Random works fine, but it doesn't randomize within the game, only between games.

回答1:

When you run actions like from your example and randomize duration parameter with something like arc4Random this is actually happening:

• Random duration is set and stored in action.
• Then action is reused in a sequence with a given duration.

Because the action is reused as it is, duration parameter remains the same over time and moving speed is not randomized.

One way to solve this (which I prefer personally) would be to create a "recursive action", or it is better to say, to create a method to run desired sequence and to call it recursively like this :

import SpriteKit

class GameScene: SKScene {

    let  shape = SKSpriteNode(color: UIColor.redColor(), size: CGSize(width: 20, height: 20))

    override func didMoveToView(view: SKView) {


       shape.position = CGPointMake(CGRectGetMidX(self.frame) , CGRectGetMidY(self.frame)+60 )

       self.addChild(shape)

       move()
    }


    func randomNumber() ->UInt32{

        var time = arc4random_uniform(3) + 1
        println(time)
        return time
    }

    func move(){

        let recursive = SKAction.sequence([

            SKAction.moveByX(frame.size.width/2.8, y: 0, duration: NSTimeInterval(randomNumber())),
            SKAction.moveByX(-frame.size.width/2.8, y: 0, duration: NSTimeInterval(randomNumber())),
            SKAction.runBlock({self.move()})])

        shape.runAction(recursive, withKey: "move")
    }

}

To stop the action, you remove its key ("move").

回答2:

I don't have any project where I can try right now.

But you might want to try this :

let action = [SKAction runBlock:^{
    double randTime = 1.5; // do your arc4random here instead of fixed value
    let moveRight = SKAction.moveByX(frame.size.width/2.8, y: 0, duration: randTime)
    let moveLeft = SKAction.moveByX(-frame.size.width/2.8, y: 0, duration: randTime)
    let texRight = SKAction.setTexture(SKTexture(imageNamed: "Drake2"))
    let texLeft = SKAction.setTexture(SKTexture(imageNamed: "Drake1"))

    let sequence = SKAction.sequence([texRight, moveRight, texLeft, moveLeft])

    Drake1.runAction(sequence)
}]; 

let repeatAction = SKAction.repeatActionForever(action)

Drake1.runAction(repeatAction)

Let me know if it helped.