在MTKView中，如何获取3D (x，y，z)中给定点的像素信息( RGB和Alpha值)？

import MetalKit

class ViewController: NSViewController, MTKViewDelegate {
    var metalView: MTKView!
    var device: MTLDevice!
    var commandQueue: MTLCommandQueue!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        device = MTLCreateSystemDefaultDevice()
        metalView = MTKView(frame: view.bounds, device: device)
        metalView.delegate = self
        view.addSubview(metalView)
        
        commandQueue = device.makeCommandQueue()
    }
    
    func draw(in view: MTKView) {
        guard let drawable = view.currentDrawable,
              let descriptor = view.currentRenderPassDescriptor else {
            return
        }
        
        let textureDescriptor = MTLTextureDescriptor.texture2DDescriptor(pixelFormat: .rgba8Unorm, width: Int(view.drawableSize.width), height: Int(view.drawableSize.height), mipmapped: false)
        let texture = device.makeTexture(descriptor: textureDescriptor)
        
        let commandBuffer = commandQueue.makeCommandBuffer()
        let commandEncoder = commandBuffer?.makeRenderCommandEncoder(descriptor: descriptor)
        
        commandEncoder?.copy(from: drawable.texture, sourceSlice: 0, sourceLevel: 0, sourceOrigin: MTLOrigin(x: 0, y: 0, z: 0), sourceSize: MTLSize(width: Int(view.drawableSize.width), height: Int(view.drawableSize.height), depth: 1), to: texture!, destinationSlice: 0, destinationLevel: 0, destinationOrigin: MTLOrigin(x: 0, y: 0, z: 0))
        
        commandEncoder?.endEncoding()
        commandBuffer?.commit()
        commandBuffer?.waitUntilCompleted()
        
        let bytesPerPixel = 4
        let bytesPerRow = bytesPerPixel * Int(view.drawableSize.width)
        let region = MTLRegionMake2D(0, 0, Int(view.drawableSize.width), Int(view.drawableSize.height))
        var pixelData = [UInt8](repeating: 0, count: bytesPerRow * Int(view.drawableSize.height))
        
        texture?.getBytes(&pixelData, bytesPerRow: bytesPerRow, from: region, mipmapLevel: 0)
        
        let pixelIndex = 3 * (x + y * Int(view.drawableSize.width))
        let red = pixelData[pixelIndex]
        let green = pixelData[pixelIndex + 1]
        let blue = pixelData[pixelIndex + 2]
        let alpha = pixelData[pixelIndex + 3]
        
        print("Pixel at (\(x), \(y)): R=\(red), G=\(green), B=\(blue), A=\(alpha)")
    }
}