I made a near seamless nether portal - New nether portal optimization made it even better

Ok so based off what I just saw you replaced the purple nether portal block with an image copied from a specific location in the nether (if you had to hard code the location that wouldn't be great but having it just use what the other side can see would be great) and put it over it but it doesn't actually load the chunks or render any nether it's just displaying an image. Then when you jump through you've gotten rid of the bells and whistles so now there is just a small moment of loading. I've never messed with Minecraft like this so I'm just wondering how you get the affect of being able to see different angles from outside the portal? Is it just the size of the image exceeds the pane?

/r/Minecraft Thread Link - v.redd.it