Improper plane reflection of geometry when viewed through portals

[Jaxxoon R]

Reflective planes don't seem to function properly when combined with plane portals, as once you leave the portal area they reside in they stop reflecting anything outside of it. As seen here, once the viewpoint crosses the portal boundary the upper area is no longer reflected by the lower one.

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I've included a map where this occurs. It's easiest to use the fly cheat to move between the portal sides repeatedly. Doing this while moving backwards fast for long enough will also cause a Doomguy sprite to move really, really quickly across the room, so quickly that I wasn't able to get a screenshot of it. I remember something similar-looking happening back when wall portals were still in their early phases.

[Graf Zahl]

Fixed. This was caused because looking down a portal masked out any subsequent upward portal. A reflective plane must invert this because it inverts the view direction.