3.7.2 Dot in the middle of the skybox revisited

[Enjay]

At the risk of pushing Graf over the edge, this bug has either semi-reared its head again, or wasn't fully fixed.

Previous bug report: viewtopic.php?f=7&t=62518&p=1079676

Though I note from the above linked thread:

After thinking about this issue for a while I had to conclude that with the portal setups out there a proper fix is plain and simply impossible.
...
So I went for the cheap route and only calculate a portal's bounding rectangle and restrict the cap to that. For most cases that should be sufficient. To break this it really needs some deliberately fucked up setup with multiple mergeable portal areas and some incompatible ones in-between.

So, maybe this is as fixed as it can be.

Anyway, again, using the original skybox example, I can still see an artefact in the middle of the sky. It doesn't appear quite so readily as it did previously. It takes a bit more running around and positioning myself to see it. I find it easiest to see in the second Episode 1 sky area (i.e. not the one where the player start spot is.) The full "dot" isn't visible either; just a bit of it.

[Apeirogon]

Well, now its change shape. At least some progress in try to eliminate this bug.

[Graf Zahl]

This time it was something far more trivial: The bounding box used to calculate the stencil cap was not properly initialized resulting in incorrect shapes.