SpriteKit - SKAction过程中精灵的正确位置

Question

我正在编写一个具有连续(横向)滚动地形的应用程序，该地形由图像动态组成。所以我创建一个精灵，把它向旁边滚动，&当它要显示它的右边缘并继续滚动时，我在它的右边添加第二个精灵，它也会滚动，等等。当它们从左边消失时，它们被移除。

问题是，当我添加新的精灵时，它之间有一个小的间隙(大约4像素)&前一个，好像在把它放到屏幕上的时间里，滚动动画移动了几个像素。

滚动类是-

import UIKit
import SpriteKit

private let lagOffset: CGFloat = 4.0 // currently, this is the only way I can get rid of the gap between terrain blocks

class GameScene: SKScene
{
    private var terrainNumber = 2
    private var followingTerrainBlock: TerrainBlock? = .None

    override init(size: CGSize)
    {
        super.init(size: size)
        // create the first terrain block
        let terrainBlock = TerrainBlock(size: Size.terrainBlock, terrainNumber: 1)
        terrainBlock.position = CGPoint(x: size.width / 2.0 + Size.terrainBlock.width, y: size.height / 2.0)
        addChild(terrainBlock)
        followingTerrainBlock = terrainBlock
        moveTerrainBlock(terrainBlock)
    }
    required init?(coder aDecoder: NSCoder)
    {
        fatalError("init(coder:) has not been implemented")
    }

    func moveTerrainBlock(terrainBlock: TerrainBlock)
    {
        // create the next terrain block on a background thread as it's quite expensive
        // it'll be ready in plenty of time for when it's needed
        GCD.async { () -> () in
            self.followingTerrainBlock = TerrainBlock(size: Size.terrainBlock, terrainNumber: self.terrainNumber)
        }

        var targetX = size.width / 2.0
        let y = terrainBlock.position.y
        let move = SKAction.moveTo(CGPoint(x: targetX, y: y), duration: Time.terrainScroll)
        // move the terrain block to centre on the screen - at this point we add the following terrain block immediately behind it, off-screen
        // the scroll animation lasts 5 seconds before the completion closure runs, by which time self.followingTerrainBlock has been ready for ages 
        terrainBlock.runAction(move) { [weak self]() -> Void in
            if let strongSelf = self
            {
                strongSelf.terrainNumber++
                // we have to put an offset into the position of the new terrain block, or there'll be a gap between the old & new blocks
                strongSelf.followingTerrainBlock!.position = CGPoint(x: targetX + Size.terrainBlock.width - lagOffset, y: y)
                strongSelf.addChild(strongSelf.followingTerrainBlock!)
                // now we tell the new terrain block to follow the existing one
                strongSelf.moveTerrainBlock(strongSelf.followingTerrainBlock!)

                // then we continue moving the existing terrain block until it's off-screen, then remove the sprite
                targetX -= Size.terrainBlock.width - lagOffset
                let move = SKAction.moveTo(CGPoint(x: targetX, y: y), duration: Time.terrainScroll)
                terrainBlock.runAction(move) { () -> Void in
                    terrainBlock.removeFromParent()
                }
            }
        }
    }
}

我想知道的是如何将以下地形块放在屏幕上，以便它们与前一个地形块的右边缘完全对齐。如果我停止动画&添加一个，位置是正确的，没有偏移，所以位置计算没有问题。

Answer 1

创建每个块时，创建一个约束(constant = 0)将其附加到前一个块…

我相信，当每个块移出视图时，约束也会解除，但您可能也必须考虑这一部分。