[2.9pre-88-g3358181] Portals causing a graphical glitch

[skyrimguy]

No graphical glitch if you are near the small building:

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The graphical glitch appears if you move away from the small building:

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I can reproduce the graphical glitch since:
https://github.com/doomtech/zdoom/commi ... 81dc588130

[Graf Zahl]

The portals are known not to be perfect, if you place them just right they glitch.

I'm a) not sure if it's actually fixable and b) this is at the very bottom of stuff to do with portals - once the basics are working.

[Graf Zahl]

I'm closing this as it'd probably require a fundamental rewrite of how portals are processed by the renderer.