为什么我的SpriteKit场景中的循环图像之间存在间隙？

一开始我已经声明了节点。

//地面节点的声明。

var groundImage: SKSpriteNode = SKSpriteNode()
var groundImage2: SKSpriteNode = SKSpriteNode()

在viewDidLoad中，我有：

    //Creates an instance of both sprites that are of the same image that are to be lined up against each other in the x axis creating the illution of continuity.

    groundImage = SKSpriteNode(imageNamed: "Ground.png")
    groundImage2 = SKSpriteNode(imageNamed: "Ground.png")

    //Specifies the Z position of the images.

    groundImage.zPosition = 3
    groundImage2.zPosition = 3

    //Scales the images to the correct size of the screen.

    groundImage.size.width = self.frame.width
    groundImage.size.height = self.groundImage.size.height / 2

    groundImage2.size.width = self.frame.width
    groundImage2.size.height = self.groundImage2.size.height / 2

    //Specicies the x position of the images.  By offsetting the second you create the illution of a long, continuous image.

    groundImage.position.x = view.bounds.size.width * 0.5
    groundImage2.position.x = view.bounds.size.width * 1.5

    //Specifies the y postion of the images, obviously these are the same as they are not to be offset at any time.

    groundImage.position.y = (view.bounds.size.height - view.bounds.size.height) + self.groundImage.size.height / 2
    groundImage2.position.y = (view.bounds.size.height - view.bounds.size.height) + self.groundImage2.size.height / 2

    //Not sure what this does yet.

    groundImage.texture?.filteringMode = SKTextureFilteringMode.Nearest
    groundImage2.texture?.filteringMode = SKTextureFilteringMode.Nearest

    //Adds instances of the sprites to the scene.

    self.addChild(groundImage)
    self.addChild(groundImage2)

在更新方法中，我有：

    //This is how the image is moved relative the number specified.  The number in the variable is how many pixels the frame is being moved each frame refresh.

    groundImage.position.x -= gameSpeed
    groundImage2.position.x -= gameSpeed

    if (groundImage.position.x <= -self.view!.bounds.size.width / 2)
    {
        groundImage.position.x = self.view!.bounds.size.width * 1.5 // - 2
    }


    if (groundImage2.position.x <= -self.view!.bounds.size.width / 2)
    {
        groundImage2.position.x = self.view!.bounds.size.width * 1.5 // - 2
    }

在循环播放时，两个图像之间还存在细微的间隙。随着我增加使用游戏速度变量循环播放它们的速度，此差距会增大。

有人可以向我解释我做错了什么吗？

我已经检查过图像本身没有引起问题。

谢谢，

史蒂文