ImageProcessor.swift

func image(from mtlTexture: MTLTexture) -> UIImage {
    //画像サイズ
    let w = mtlTexture.width
    let h = mtlTexture.height
    let bytesPerPixel: Int = 4
    let imageByteCount = w * h * bytesPerPixel
    let bytesPerRow = w * bytesPerPixel
    var src = [UInt8](repeating: 0, count: Int(imageByteCount))
    //CGImageに変換
    let region = MTLRegionMake2D(0, 0, w, h)
    mtlTexture.getBytes(&src, bytesPerRow: bytesPerRow, from: region, mipmapLevel: 0)
    let bitmapInfo = CGBitmapInfo(rawValue: (CGBitmapInfo.byteOrder32Big.rawValue | CGImageAlphaInfo.premultipliedLast.rawValue))
    let colorSpace = CGColorSpaceCreateDeviceRGB()
    let bitsPerComponent = 8
    let context = CGContext(data: &src,
                            width: w,
                            height: h,
                            bitsPerComponent: bitsPerComponent,
                            bytesPerRow: bytesPerRow,
                            space: colorSpace,
                            bitmapInfo: bitmapInfo.rawValue)
    let cgImage = context?.makeImage()
    //UIImageに変換して返す
    let image = UIImage(cgImage: cgImage!)
    return image
}