Embed Notice

In the example you gave, the guy very pointedly rewrote the engine to make sure that the velocity of the object entering the portal is relative to that portal, specifically, which I suppose makes sense since the re-orientation is basically just making the velocity relative to the portal exiting.

However, it doesn't follow from the logic these engines actually use, which is that objects have a velocity that's not really relative to anything. It's basically a given value.