     
     // MARK: - ivars
     
-    internal var _device: MTLDevice?
-    internal var _library: MTLLibrary?
-    internal var _commandQueue: MTLCommandQueue?
     
     internal var _texture: MTLTexture?
     

    internal var _bufferHeight: Int = 0
    internal var _bufferFormatType: OSType = OSType(kCVPixelFormatType_32BGRA)
    internal var _presentationFrame: CGRect = .zero
    fileprivate var _renderPassDescriptor: MTLRenderPassDescriptor = MTLRenderPassDescriptor()
    
    internal var _ciContext: CIContext?
    internal var _pixelBufferPool: CVPixelBufferPool?
    internal var _videoBufferOutput: CVPixelBuffer?
    
    #if USE_ARKIT
    internal weak var _arView: ARSCNView?

    internal var _renderer: SCNRenderer?
    
    // MARK: - object lifecycle
    fileprivate var _ciContext: CIContext?
    fileprivate var _pixelBufferPool: CVPixelBufferPool?
    fileprivate var _videoBufferOutput: CVPixelBuffer?
    
    public convenience init(view: ARSCNView) {
        self.init()
