ZDoom

Indeed, much better. I got a strange variant of halls of mirrors with r1332 and a 1024x1024 sky texture (it seemed like some triangles were HOMing, others not), now it looks normal.

Should be better now. I reworked the coordinate calculations for oversized skies (larger than 240 pixels. The old code wasn't meant to work for anything taller than 256 pixels.

It's a sphere, not a cylinder. It's made of triangles like a geodesic dome. The shape is a bit weird in that the upper hemisphere covers about everything, the lower hemisphere only plugs a tiny hole at the bottom (as shown on the OP's pic).

What is the equivalent skybox for how GZDoom renders the skies natively? How large should that cylinder be, where is the camera placed? I know this post would be better for the drdteam forum, but I don't want to destroy the equivalent thread there.

Well, such tall skies were never considered when the function was written

You can try.

Would you recommend an official suggestion on yon GZDoom forum, then?

Unless Graf does it, it won't happen.

What about a new MapInfo key (GZDoom specific, ZDoom ignored) to enable single-image sky?

Looking into gl_skydome.cpp, this appears to be by design. The RenderDome() function calls another function called RenderSkyHemisphere() twice, once for the upper hemisphere and the second time for the lower hemisphere.

So it's not so much that it wraps or tiles the texture, it's just that it draws it twice, independently of texture size.

I'm not going to change anything about how it works.

Closing because GZDoom has its own bugs forum. (And bumping so it might get noticed by somebody who might do something with it.)

I've noticed this too. AFAIK, the height of the texture is not taken into account at all, and the sky texture is always tiled downward once.

Spoiler:

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If a sky is exactly 544px tall it's big enough to fill in all of ZDoom's freelook space and lever wrap (Edit: and never wrap). However GZDoom still insists on making it wrap once, which makes it look like a mess.