Hello dear authors
I made this attempt to test a workaround linked to this note in your book
« SpriteKit rendering in Metal
Note: As of the time of writing, CIContext.render hangs the app when using Xcode 11 or macOS Catalina 10.15. However, you can still do the rest of this chapter using Xcode 10 on macOS Mojave 10.14. »
At the end of init(metalView:) in Renderer I added
metalView.framebufferOnly = false
and in postProcess(inputTexture:) of extension HudNode I changed this line
context.render(outputImage, to: outputTexture, commandBuffer: commandBuffer, bounds: outputImage.extent, colorSpace: colorSpace)
to this line (wanting to force CIImage to use its own CommandBuffer)
context.render(outputImage, to: outputTexture, commandBuffer: nil , bounds: outputImage.extent, colorSpace: colorSpace)
And well … it’s working so far. May it is not ideal … maybe next pages it will not work anymore but… you know, just sharing 
