SKAction 跟随路径在两个圆圈(八形)中无法按预期工作

Question

我正在尝试创建一个形状为八或无穷大符号的CGPath。我确实认为路径创建应该返回所需的结果，但我仍然会在这里发布它：

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

现在我有另一个节点应该遵循这条路径，我认为通过使用 SKAction 就可以工作，如下所示：

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，形状是我分配路径的 SKShapeNode 的名称。但是，节点只绘制其中一个圆，而不是所需的形状。我一直在谷歌上搜索这个问题，但找不到任何类似的案例，现在已经坐了一个多天，所以我可能看不到明显的东西。任何见解将不胜感激！

Answer 1

如果你画出你生成的数字 8，你会看到你的角色只沿着底部的圆圈，因为这是你绘制路径的方式。

您需要从顶部/底部到中间绘制顶部或底部圆的一半，然后在中间开始和结束添加完整的其他圆，最后将另一个半圆返回到开始的位置。

下面是一个示例，它还绘制了边界矩形和要遵循的数字 8 路径：

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 - drawSKShapeNode - 你不需要它，但对于调试很有用，因为它们通过从给定的内容创建SKShapeNode来"绘制"CGPath或CGRect。