如何在mac上获取当前可提取金属的快照？

import Metal
import MetalKit

class Renderer: NSObject, MTKViewDelegate {
    var device: MTLDevice
    var commandQueue: MTLCommandQueue

    init(metalKitView: MTKView) {
        device = metalKitView.device!
        commandQueue = device.makeCommandQueue()!
        super.init()
        metalKitView.device = device
        metalKitView.delegate = self
    }

    func mtkView(_ view: MTKView, drawableSizeWillChange size: CGSize) {}

    func draw(in view: MTKView) {
        guard let drawable = view.currentDrawable,
              let renderPassDescriptor = view.currentRenderPassDescriptor else { return }

        let commandBuffer = commandQueue.makeCommandBuffer()!
        let renderEncoder = commandBuffer.makeRenderCommandEncoder(descriptor: renderPassDescriptor)!

        // 在这里添加渲染命令

        renderEncoder.endEncoding()
        commandBuffer.present(drawable)
        commandBuffer.commit()
    }
}