SKAction followPath无法按预期方式与两个圆形一起工作（Eight Shape）

Question

我正在尝试创建一个带有八个或无限符号形状的CGPath。我的确认为路径创建应该返回所需的结果，但我还是会张贴在这里：

let path = CGMutablePath() 

path.addEllipse(in: CGRect(x: -height/4, y: -height/2, width: height/2, height: height/2)) 
path.addEllipse(in: CGRect(x: -height/4, y: 0.0, width: height/2, height: height/2)) 

path.closeSubpath() 

return path 

现在我应该走这条路，我本以为这只是使用SKAction像这样工作的另一个节点：

highlighter.run(SKAction.repeatForever(SKAction.follow(shape.path!, asOffset: false, orientToPath: true, duration: 5.0))) 

荧光笔是我的节点的名称，形状是SKShapeNode的名称，我已将它分配给我的路径。然而节点只绘制其中一个圆圈而不是所需的形状。我一直在搜索这个问题，但找不到任何类似的案例，现在已经坐了一整天，所以我可能看不到明显的东西。任何有识之士将非常感谢！

Answer 1

如果您绘制已生成的图8，则会看到您的精灵只在底部圆圈之后，因为这是您绘制路径的方式。

您需要画出顶部或底部圆的一半，从顶部/底部到中间，然后添加从中间开始和结束的完整另一个圆，最后再添加另一个半圆回到您开始的位置。

下面是一个例子，这也吸引了边框和8字型道路可走：

class GameScene: SKScene { 

    // var sprite = SKSpriteNode() 
    var figureEightPath = CGMutablePath() 

    override func didMove(to view: SKView) { 

     let boundingRect = CGRect(x: -200, y: -400, width: 400, height: 800) 
     addChild(drawSKShapeNode(fromRect: rect, withWidth: 2, inColour: SKColor.green, called: "rect")) 

     figureEightPath = drawFigureEight(in: boundingRect) 
     addChild(drawSKShapeNode(fromPath: figureEightPath, withWidth: 2, inColour: SKColor.red, called: "path")) 

     let sprite = SKSpriteNode(color: SKColor.yellow, size: CGSize(width: 50, height: 50)) 
     addChild(sprite) 

     let moveAction = SKAction.follow(figureEightPath, asOffset: false, orientToPath: true, speed: 200) 
     sprite.run(SKAction.repeatForever(moveAction)) 

    } 

    func drawSKShapeNode(fromPath path: CGMutablePath, 
         withWidth width: CGFloat, 
         inColour colour: SKColor, 
         called name: String) -> SKShapeNode { 

     let shape = SKShapeNode(path: path, centered: true) 
     shape.lineWidth = width 
     shape.strokeColor = colour 
     shape.name = name 
     return shape 
    } 

    func drawSKShapeNode(fromRect rect: CGRect, 
         withWidth width: CGFloat, 
         inColour colour: SKColor, 
         called name: String) -> SKShapeNode { 

     let shape = SKShapeNode(rect: rect) 
     shape.lineWidth = width 
     shape.strokeColor = colour 
     shape.name = name 
     return shape 
    } 

    func drawFigureEight(in rect: CGRect) -> CGMutablePath { 
     let bottomCentre = CGPoint(x: rect.midX, y: rect.height/4+rect.minY) 
     let topCentre = CGPoint(x: rect.midX, y:(rect.height/4)*3+rect.minY) 
     let radius = rect.height/4 

     let bottom = CGPoint(x: rect.midX, y: rect.minY) 

     let path = CGMutablePath() 
     path.move(to: bottom) 
//Draw a semi-circle from the bottom counter-clockwise to the middle 
     path.addArc(center: bottomCentre, radius: radius, startAngle: CGFloat(Double.pi*1.5), endAngle: CGFloat(Double.pi/2), clockwise: false) 
//Draw to top circle in a clockwise direction 
     path.addArc(center: topCentre, radius: radius, startAngle: CGFloat(Double.pi*1.5), endAngle: CGFloat(-Double.pi/2), clockwise: true) 
//Draw the rest of the bottom circle by drawing a semi-circle from the middle to the bottom counter-clockwise. 
     path.addArc(center: bottomCentre, radius: radius, startAngle: CGFloat(Double.pi/2), endAngle: CGFloat(-Double.pi/2), clockwise: false) 

     return path 
    } 

    override func update(_ currentTime: TimeInterval) { 
     // Called before each frame is rendered 
    } 
} 

有几个辅助函数的 - drawSKShapeNode - 你将不再需要，但有用调试，因为他们通过创建SKShapeNode来绘制CGPath或CGRect。