在视图的每一侧对齐四个caemitterlayer（），向内指向

Question

我正在为子视图添加4 caemitterlayers。每个caemitterlayer都是一行，将位于每一侧。旋转将通过CGAFFINETRANSFORM 控制

问题：

我无法获得.left和.rigrt。

我的 >这是我的进步：

override func awakeFromNib() {
    super.awakeFromNib()
    self.layer.cornerRadius = GlobalConstants.smallCornerRadius
    createParticles(direction: .Up)
    createParticles(direction: .Down)
    createParticles(direction: .Left)
    createParticles(direction: .Right)
}

enum EmitTo {
    case Up
    case Down
    case Left
    case Right
}

func createParticles(direction: EmitTo) {
    self.layoutSubviews()
    let particleEmitter = CAEmitterLayer()
    particleEmitter.position = CGPoint(x: self.bounds.midX, y: self.bounds.midY)
    particleEmitter.bounds = CGRect(x: 0, y: 0, width: self.bounds.size.width, height: self.bounds.size.height)
    
    
    if direction == .Up {
        particleEmitter.setAffineTransform(CGAffineTransform(rotationAngle: 0))
    } else if (direction == .Down) {
        particleEmitter.setAffineTransform(CGAffineTransform(rotationAngle: .pi))
    } else if (direction == .Left) {
        particleEmitter.setAffineTransform(CGAffineTransform(rotationAngle: .pi / 2))
    } else if (direction == .Right) {
        particleEmitter.setAffineTransform(CGAffineTransform(rotationAngle: -.pi / 2))
    }
    
    if direction == .Up || direction == .Down {
        particleEmitter.emitterPosition = CGPoint(x: self.frame.width / 2, y: 0)
    }
    if direction == .Left {
        particleEmitter.emitterPosition = CGPoint(x: self.frame.height / 2, y: self.frame.height)
    }
    if direction == .Right {
        particleEmitter.emitterPosition = CGPoint(x: self.frame.height / 2, y: -50)
    }
    
    
    particleEmitter.emitterSize = self.bounds.size
    particleEmitter.emitterShape = CAEmitterLayerEmitterShape.line
    particleEmitter.zPosition = 1
    
    let triangle = makeEmitterCell(direction: direction)
    particleEmitter.emitterCells = [triangle]

    self.layer.addSublayer(particleEmitter)
}

func makeEmitterCell(direction: EmitTo) -> CAEmitterCell {
    let cell = CAEmitterCell()
    cell.birthRate = 25
    cell.lifetime = 3
    cell.lifetimeRange = 0
    cell.velocity = 10
    cell.velocityRange = 5
    cell.emissionLongitude = .pi
    
    cell.spin = 2
    cell.spinRange = 3
    cell.scale = 0.4
    cell.scaleRange = 0.6
    cell.scaleSpeed = -0.10

    cell.contents = UIImage(named: "greenTriangle")?.cgImage
    return cell
}

正在发生的事情：

https://i.sstatic.net/0r8qu.gif“ alt =“粒子系统的gif动画”>

我的问题

我如何获得.left> .left和.right caemitterlayer与灰色视图的左侧和右侧正确对齐？

绿色三角形图像：

Answer 1

您尝试使用CGAFFINETRANSFORM的方法是有希望的，因为线发射器是仅具有宽度维度的水平线。通过旋转它，您可以将其从左侧或右侧发射。

但是，您需要将视图高度作为宽度和视图宽度作为高度使用发射极界限。

particleEmitter.bounds = CGRect(x: 0, y: 0, width: bounds.size.height, height: bounds.size.width)

因此，将发射的宽度设置为视图高度：

particleEmitter.emitterSize = CGSize(width: bounds.size.height, height: 0)

必须以相同的方式调整发射极位置。

为什么这样？查看以下图表，顶部发射：

​而且，排放量也不可见，因为它们会在左边很大。

将发射器在左侧或右侧的距>。

当然，从顶部和底部发出的发射器应获得正常的界限，只需要像您的问题中那样旋转。

提示

在您的createparticles方法您调用self.layoutsubviews（）。应该避免。

Apple Docs明确说明：

您不应该直接调用此方法。

请参阅 httpps：// https：//developer.apple.apple.com/documenter.com/documentation/uikitation/uikit/uikit/uikit/uiview/1666222224242 -layoutsubviews 。

取而代之的是，您可以覆盖layoutsubviews，然后从那里调用createparticles方法。确保通过删除任何先前创建的发射极层。

一件小事：Swift Switch Case从约定的小写字母开始。

代码

一个完整的示例可以帮助您入门，然后看起来像这样：

import UIKit

class EmitterView: UIView {
    
    private var emitters = [CAEmitterLayer]()
    
    enum EmitTo {
        case up
        case down
        case left
        case right
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        emitters.forEach { $0.removeFromSuperlayer() }
        emitters.removeAll()
        createParticles(direction: .up)
        createParticles(direction: .down)
        createParticles(direction: .left)
        createParticles(direction: .right)
    }
    
    func createParticles(direction: EmitTo) {
        let particleEmitter = CAEmitterLayer()
        emitters.append(particleEmitter)
        particleEmitter.position = CGPoint(x: bounds.midX, y: bounds.midY)
        particleEmitter.emitterShape = .line

        switch direction {
        case .up, .down:
            particleEmitter.bounds = self.bounds
            particleEmitter.emitterPosition = CGPoint(x: bounds.size.width / 2, y: 0)
            particleEmitter.emitterSize = CGSize(width: bounds.size.width, height: 0)
            if direction == .up {
                particleEmitter.setAffineTransform(CGAffineTransform(rotationAngle: -.pi))
            }
        case .left, .right:
            particleEmitter.bounds = CGRect(x: 0, y: 0, width: bounds.size.height, height: bounds.size.width)
            particleEmitter.emitterPosition = CGPoint(x: bounds.height / 2, y: 0)
            particleEmitter.emitterSize = CGSize(width: bounds.size.height, height: 0)
            let rotationAngle: CGFloat = direction == EmitTo.left ?  -.pi / 2 : .pi / 2
            particleEmitter.setAffineTransform(CGAffineTransform(rotationAngle: rotationAngle))
        }
        particleEmitter.emitterCells = [makeEmitterCell()]
        
        layer.addSublayer( particleEmitter)
    }
    
    func makeEmitterCell() -> CAEmitterCell {
        let cell = CAEmitterCell()
        cell.birthRate = 25
        cell.lifetime = 3
        cell.lifetimeRange = 0
        cell.velocity = 10
        cell.velocityRange = 5
        cell.emissionLongitude = .pi
        
        cell.spin = 2
        cell.spinRange = 3
        cell.scale = 0.4
        cell.scaleRange = 0.6
        cell.scaleSpeed = -0.10
        
        cell.contents = UIImage(named: "greenTriangle")?.cgImage
        return cell
    }
}

test