Quick example using a SCNRenderer and Metal to render a scene offscreen to a MTLTexture that's then displayed in another scene. Much like Portal (the game), well kind of.
The rendered image displayed as a texture in the bottom SCNView is quite pixelated due to using a small texture size, there's no problem bumping this up.
Interesting parts are found in the doRender function, with boilerplate code in the setupMetal and setupTexture functions. As the code shows, this was rather trivial to setup.
MIT