quintopia wrote:Judging by the sorts of things done with cheats on, I expect that the portalable surfaces are decided by which texture is on them.
Correct, it's in the material definition files: %noportal 1. With teh new SDK this shoudl now be useable by everyone, and prevent the horrid func_noportal_volume workaround used by hacked up maps previously.
quintopia wrote:However, portals never stuck to moving objects. . .ever.
This doesn't make sense, really, as presumably portals should remain stuck to the surface they're on regardless of its motion. (They are all on a moving earth, after all.) This is probably just a product of how computationally expensive it would be to continue rendering a portal while it was moving. So, in theory, moving portals are possible, but we aren't going to see them any time soon.
You're right, it's a technical limitation. When a portal is placed there are a bunch of physics calculations to do, which is fine for one portal but not fine to recalculate every frame for a moving portal. There are also a lot of border-cases that would need to be worked out; what happens if two portals face each other, then move closer together until a box in the middle collides with itself? Intersecting objects are problematical under havoc normally, intersecting faces from one object... ick.
So while it should be do-able with a mod don't expect it to happen anytime soon; a more likely scenario is Valve will code up some very specific moving-portal situations, instead of a general moving portal solution.