I've created a portal based on this method. Here's what it looks like:
Light passing through the portal is not handled accurately; instead I've faked it by baking the light from the outside onto the outer side of the portal, and then applying the baked texture onto the inner side.
Now, the problem is that, as you can see, the two parts of the cylinder sticking through the portal do not match up, since they are lighted differently.
Is there any way I can get the light on the cylinder to work correctly?