视图内存问题上的多个 CAMetalLayer

Question

我正在开发一个需要添加多个 CAMetaLayers 并在其中绘制不同形状的应用程序。 渲染是独立进行的，每个元素都可以更改。 我需要在不同的图层上渲染纹理，因为 UIView 也包含通常的 CALayers 并且顺序对我很重要。 问题是通过调用 nextDrawable() 分配了内存并且有大量的层，内存使用了很多。 是否有可能通过绘制图层来释放此内存，直到下一次绘图并保留图层的内容？ 我从 raywenderlich 那里借用了调整示例。 https://www.raywenderlich.com/7475-metal-tutorial-getting-started

class ViewController: UIViewController {
  let vertexData:[Float] =
    [0.0, 1.0, 0.0,
     -1.0, -1.0, 0.0,
     1.0, -1.0, 0.0]
  
  var device: MTLDevice!
  var metalLayer: CAMetalLayer!
  var vertexBuffer: MTLBuffer!
  var pipelineState: MTLRenderPipelineState!
  var commandQueue: MTLCommandQueue!
  var timer: CADisplayLink!
  
  private var createTimer: Timer?
  
  @objc private func addNewMetalLayer() {
    self.metalLayer = CAMetalLayer()          // 1
    self.metalLayer.device = self.device           // 2
    self.metalLayer.pixelFormat = .bgra8Unorm // 3
    self.metalLayer.framebufferOnly = true    // 4
    self.metalLayer.frame = view.layer.frame  // 5
    view.layer.addSublayer(self.metalLayer)   // 6
    
    print("\(self.view.layer.sublayers)")
  }
  
  override func viewDidLoad() {
    super.viewDidLoad()
    
    device = MTLCreateSystemDefaultDevice()
    self.addNewMetalLayer()
    let dataSize = vertexData.count * MemoryLayout.size(ofValue: vertexData[0]) // 1
    vertexBuffer = device.makeBuffer(bytes: vertexData, length: dataSize, options: []) // 2
    
    // 1
    let defaultLibrary = device.makeDefaultLibrary()!
    let fragmentProgram = defaultLibrary.makeFunction(name: "basic_fragment")
    let vertexProgram = defaultLibrary.makeFunction(name: "basic_vertex")
    
    // 2
    let pipelineStateDescriptor = MTLRenderPipelineDescriptor()
    pipelineStateDescriptor.vertexFunction = vertexProgram
    pipelineStateDescriptor.fragmentFunction = fragmentProgram
    pipelineStateDescriptor.colorAttachments[0].pixelFormat = .bgra8Unorm
    
    // 3
    pipelineState = try! device.makeRenderPipelineState(descriptor: pipelineStateDescriptor)
    
    commandQueue = device.makeCommandQueue()
    
    timer = CADisplayLink(target: self, selector: #selector(gameloop))
    timer.add(to: RunLoop.main, forMode: .default)
    
    self.createTimer = .scheduledTimer(timeInterval: 3.0, target: self, selector: #selector(addNewMetalLayer), userInfo: nil, repeats: true)
  }
  
  func render() {
    guard let drawable = metalLayer?.nextDrawable() else { return }
    let renderPassDescriptor = MTLRenderPassDescriptor()
    renderPassDescriptor.colorAttachments[0].texture = drawable.texture
    renderPassDescriptor.colorAttachments[0].loadAction = .clear
    renderPassDescriptor.colorAttachments[0].clearColor = MTLClearColor(red: 0.0, green: 104.0/255.0, blue: 55.0/255.0, alpha: 1.0)
    
    let commandBuffer = commandQueue.makeCommandBuffer()!
    let renderEncoder = commandBuffer.makeRenderCommandEncoder(descriptor: renderPassDescriptor)!
    renderEncoder.setRenderPipelineState(pipelineState)
    renderEncoder.setVertexBuffer(vertexBuffer, offset: 0, index: 0)
    renderEncoder.drawPrimitives(type: .triangle, vertexStart: 0, vertexCount: 3, instanceCount: 1)
    renderEncoder.endEncoding()
    
    commandBuffer.present(drawable)
    commandBuffer.commit()
  }
  
  @objc func gameloop() {
    autoreleasepool {
      self.render()
    }
  }
}