CAEmitterLayer多小区交织

Question

我有一个CAEmitterLayer和一个CAEmitterCell数组，我希望每个单元格的输出都混合在一起。现在，数组中的第一个单元格总是绘制在其他单元格之上。

我已经调整了层的renderMode和每个单元格的zAcceleration，但都没有解决这个问题。

一些示例代码：

func layoutSubviews() {
    // ...
    emitterLayer.frame = self.bounds
    emitterLayer.seed = UInt32(Date().timeIntervalSinceNow)
    emitterLayer.renderMode = kCAEmitterLayerOldestFirst
    emitterLayer.emitterPosition = CGPoint(x: bounds.midX, y: bounds.midY)
    emitterLayer.emitterSize = CGSize.init(width: bounds.width, height: 0)
    emitterLayer.emitterShape = kCAEmitterLayerLine
    self.layer.addSublayer(emitterLayer)
}

private func animate() {
    // ...
    if emitterLayer.emitterCells == nil || emitterLayer.emitterCells?.count == 0 {
        let cells = (1...8).map { i -> CAEmitterCell in
            if let img = UIImage.init(named: "Slice-\(i)") {
                return createEmitterCell(image: img, index: i)
            } else {
                fatalError()
            }
        }
        emitterLayer.emitterCells = cells
    }
}

private func createEmitterCell(image: UIImage, index: Int) -> CAEmitterCell {
    let cell = CAEmitterCell.init()
    cell.isEnabled = true
    cell.contents = image.cgImage

    cell.contentsRect = CGRect(origin: CGPoint.zero, size: CGSize(width: 1, height: 1))

    cell.birthRate = Float(index)
    cell.lifetime = 3
    cell.velocity = 7
    cell.velocityRange = 3
    cell.scale = 0.5

    cell.emissionRange = (95 * CGFloat.pi / 180.0)
    cell.emissionLatitude = (27 * CGFloat.pi / 180.0)
    cell.emissionLongitude = (139 * CGFloat.pi / 180.0)

    cell.xAcceleration = 10.0
    cell.yAcceleration = 100.0
    cell.zAcceleration = 10 * CGFloat(index)

    return cell
}

Answer 1

我有12个发射器单元，我的解决方案是随机化发射器的顺序。这样，应用程序的每次运行都会产生不同的排序。

        emojiCells = "✨✅"
            .characters
            .sorted(by: { (a, b) -> Bool in
                return arc4random() % 2 == 0
            }).enumerated().map({ (offset: Int, element: Character) -> CAEmitterCell in
                // create emitter cells for each emoji
                let raster = rasterize(emoji: element)
                return createEmitterCell(image: raster, index: offset)
            })
        emitterLayer.emitterCells = emojiCells

如果我有较少的发射极细胞，那么我会在彼此周围包含重复的发射器。比如[cell1, cell2, cell1]。在这种情况下，其他调整也会有所帮助，比如提高cell2的出生率。