如何将两个CIImages与alpha组合在一起？

import CoreImage

func combineImagesWithAlpha(image1: CIImage, image2: CIImage) -> CIImage? {
    // 创建alphaCompositing滤镜
    guard let alphaCompositingFilter = CIFilter(name: "CISourceOverCompositing") else {
        return nil
    }
    
    // 设置输入图像
    alphaCompositingFilter.setValue(image1, forKey: kCIInputImageKey)
    alphaCompositingFilter.setValue(image2, forKey: kCIInputBackgroundImageKey)
    
    // 获取合并后的图像结果
    guard let outputImage = alphaCompositingFilter.outputImage else {
        return nil
    }
    
    return outputImage
}

// 示例用法
let image1 = CIImage(image: UIImage(named: "image1.png")!)!
let image2 = CIImage(image: UIImage(named: "image2.png")!)!

if let combinedImage = combineImagesWithAlpha(image1: image1, image2: image2) {
    // 处理或显示合并后的图像
    // ...
}