iOS（Swift）初始化后更改 CAEmitterCell 的屬性

Question

我的目標是使用CAEmitterLayer創建火焰效果，其強度可以通過更改其給定CAEmitterCells的alphaSpeed屬性的值來改變。 較小的alphaSpeed值會導致“咆哮”的火焰，而較大的值會抑制火焰。

到目前為止，我有一個名為FireEmitterLayer的CAEmitterLayer的子類，它的初始化程序如下：

convenience init(view: UIView) {
    self.init()
    emitterPosition = CGPoint(x: 0.5 * view.bounds.width, y: view.bounds.height)
    emitterSize = CGSize(width: view.bounds.width, height: 0.05 * view.bounds.height)
    renderMode = .additive
    emitterShape = .line
    emitterCells = fireEmitterCells
 }

發射器單元是為代表 30x30 火焰圖像的UIImage數組生成的：

private var fireEmitterCells: FireEmitterCells {
    var emitterCells = FireEmitterCells()
    for assetIdentifier in assetIdentifiers {
        let emitterCell = fireEmitterCell(for: assetIdentifier)
        emitterCells.append(emitterCell)
    }
    return emitterCells
}

每個單元格都是使用此方法創建的：

private func fireEmitterCell(for assetIdentifier: UIImage.AssetIdentifier) -> CAEmitterCell {
    let fireEmitterCell = CAEmitterCell()
    fireEmitterCell.contents = UIImage(assetIdentifier: assetIdentifier).resized(to: CGSize(width: 20.0, height: 20.0)).cgImage
    fireEmitterCell.alphaSpeed = -0.3
    fireEmitterCell.birthRate = fireBirthRate
    fireEmitterCell.lifetime = fireLifetime
    fireEmitterCell.lifetimeRange = 0.5
    fireEmitterCell.color = UIColor.init(red: 0.8, green: 0.4, blue: 0.2, alpha: 0.6).cgColor
    fireEmitterCell.emissionLongitude = .pi
    fireEmitterCell.velocity = 80.0
    fireEmitterCell.velocityRange = 5.0
    fireEmitterCell.emissionRange = 0.5
    fireEmitterCell.yAcceleration = -200.0
    fireEmitterCell.scaleSpeed = 0.3
    return fireEmitterCell
}

有沒有辦法從這個子類的實例更改這些單元格的alphaSpeed值，例如在某些UIViewController中稱為fireEmitterLayer ：

var fireEmitterLayer = FireEmitterLayer(view: view)

我嘗試在FireEmitterLayer類中添加此方法

private func setAlphaSpeed(_ alphaSpeed: Float) {
    guard let emitterCells = emitterCells else { return }
    for emitterCell in emitterCells {
        emitterCell.alphaSpeed = alphaSpeed
    }
}

但這不起作用...

任何幫助表示贊賞:-)

Answer 1

每當我想使用 func 時，我都會為我的發射器動態設置我的單元格，如下所示：

func makeEmitterCell(thisEmitter : CAEmitterLayer, newColor: UIColor, priorColor: UIColor, contentImage : UIImage) -> CAEmitterCell {

    let cell = CAEmitterCell()

    cell.birthRate = lastChosenBirthRate
    cell.lifetime = lastChosenLifetime
    cell.lifetimeRange = lastChosenLifetimeRange
    //cell.color = newColor.cgColor
    cell.emissionLongitude = lastChosenEmissionLongitude
    cell.emissionLatitude = lastChosenEmissionLatitude
    cell.emissionRange = lastChosenEmissionRange
    cell.spin = lastChosenSpin
    cell.spinRange = lastChosenSpinRange
    cell.scale = lastChosenScale
    cell.scaleRange = lastChosenScaleRange
    cell.scaleSpeed = lastChosenScaleSpeed
    cell.alphaSpeed = Float(lastChosenAlphaSpeed)
    cell.alphaRange = Float(lastChosenAlphaRange)
    cell.autoreverses = lastChosenAutoReverses
    cell.isEnabled = lastChosenIsEnabled
    cell.velocity = lastChosenVelocity
    cell.velocityRange = lastChosenVelocityRange
    cell.xAcceleration = lastChosen_X_Acceleration
    cell.yAcceleration = lastChosen_Y_Acceleration
    cell.zAcceleration = 0
    cell.contents = contentImage.cgImage

    //Access the property with this key path format: @"emitterCells.<name>.<property>"
    cell.name = "myCellName"
    let animation = CABasicAnimation(keyPath: "emitterCells.myCellName.color")
    animation.fromValue = priorColor.cgColor
    animation.toValue = newColor.cgColor
    animation.duration = CFTimeInterval(cellAnimationTimeValue)

    if thisEmitter == particleEmitter_1
    {
        particleEmitter_1.add(animation, forKey: "emitterCells.myCellName.color")
    }
    if thisEmitter == particleEmitter_2
    {
        particleEmitter_2.add(animation, forKey: "emitterCells.myCellName.color")
    }

    return cell
} // ends makeEmitterCell

在該功能的末尾，我的設計有一個彩色動畫，您可以通過某種方式獲得獎勵代碼。

我保留這些變量以允許我動態控制單元格功能；

var lastChosenBirthRate : Float = 300
var lastChosenLifetime : Float = 3
var lastChosenLifetimeRange : Float = 0
var lastChosenEmissionLongitude : CGFloat = 2 * CGFloat.pi
var lastChosenEmissionLatitude : CGFloat = 2 * CGFloat.pi
var lastChosenEmissionRange : CGFloat = 2 * CGFloat.pi
var lastChosenSpin : CGFloat = 1
var lastChosenSpinRange : CGFloat = 0
var lastChosenScale : CGFloat = 1
var lastChosenScaleRange : CGFloat = 0
var lastChosenScaleSpeed : CGFloat = -0.3
var lastChosenAlphaSpeed : CGFloat = -0.1
var lastChosenAlphaRange : CGFloat = 0
var lastChosenAutoReverses : Bool = false
var lastChosenIsEnabled : Bool = true
var lastChosenVelocity : CGFloat = 20
var lastChosenVelocityRange : CGFloat = 0
var lastChosen_X_Acceleration : CGFloat = 0
var lastChosen_Y_Acceleration : CGFloat = 0

我在我的代碼中的幾個地方制作了發射器單元。 這是一個。 此函數的一部分制作發射器單元並將它們設置為所需的發射器：

func changeParticlesCellImageRightNow(thisEmitter : CAEmitterLayer, thisContentImage : UIImage, theColor : UIColor)
{
    var priorColorToPassDown = UIColor()

    if thisEmitter == particleEmitter_1
    {
        priorColorToPassDown = lastColorUsedEmitter1
    }
    if thisEmitter == particleEmitter_2
    {
        priorColorToPassDown = lastColorUsedEmitter2
    }

    let color1 = makeEmitterCell(thisEmitter: thisEmitter, newColor: theColor, priorColor: priorColorToPassDown, contentImage: thisContentImage)

    thisEmitter.emitterCells = [color1]

}  // ends changeParticlesCellImageRightNow

這是對該函數的調用：

    // Force the change to occur right now, using the existing colors
    changeParticlesCellImageRightNow(thisEmitter : particleEmitter_1, thisContentImage : emitter_1_Image, theColor : lastColorUsedInGeneral)
    changeParticlesCellImageRightNow(thisEmitter : particleEmitter_2, thisContentImage : emitter_2_Image, theColor : lastColorUsedInGeneral)

這是發射器層對象

let particleEmitter_1 = CAEmitterLayer()
let particleEmitter_2 = CAEmitterLayer()

您可能能夠以類似的方式拼湊出一種方法，將發射器細胞的出生率、速度、速度范圍、alpha 速度、比例、比例范圍、比例速度等設置為最適合咆哮或抑制。 很大程度上取決於您在頂層的靈活性。