2024 Edit: Sorry for abandoning this immediately after releasing it. I've just learned that it apparently doesn't work with recent versions of Project Atlas - if you're hellbent on using it despite that, please see the comments here and on the Moonrain Edition (which is slightly less outdated) for ideas on how to fix it.

Also, do bear in mind this is a bit of a compatibility nightmare - I significantly moved the interiors of a few cantons, and if anything reverts those changes you'll probably end up underwater. And the interiors will be dark if you've ever entered them before on your save file (I have seen a few comments with workarounds for that).

One day I'll revisit this. Maybe in another four years. I'm sure eventually something like OpenMW will allow for a much less hacky implementation, too - maybe it does already, I haven't checked recently.


Original 2020 Description:

I highly recommend the Moonrain Edition!

Note: Might only work properly for plaza interiors you haven't previously entered on your save file. You'll be fine if you didn't go to/explore Vivec's plazas yet, but otherwise you'll probably need to save this one for your next character. Please do let me know if there's a trick to getting the game to 'forget' about interior lighting.

The vanilla game's closed Vivec canton plazas are very depressing. Open cantons are a big improvement, especially since we know from concept art and Molag Mar that they're Bethesda's original vision. But even 18 years after Morrowind's release, I can't run open cantons with a heavy modlist or something like Dramatic Vivec without my performance dying. So this is my compromise: glass domes of Vivec.

Now, all the cantons except the Arena and Temple have glass tops. The interiors have been marked as acting as exteriors, a la Mournhold, so they're lit by the sun through big mostly-transparent glass domes, and react to the weather and time of day. The Saints statues are visible from their respective plazas. The exterior domes are also transparent, but much less so - this is because I've grossly stolen gratefully adapted the hard work of Atrayonis to place a few prominent statics into the exteriors to create the illusion of peering into the plaza itself, with minimal performance hit. It's very similar to the crude LOD models used by newer, levitationless Bethesda games, but hidden by a big sheet of murky green glass.

Overall, I hope this mod brightens the mood of the plazas without affecting performance.

Requirements:
You'll need a Vivec/Velothi Atlas texture from Project Atlas; Intelligent Textures or similar, since my canton meshes exclusively come in the atlased variety.

Installation:
Use your preferred method of getting the .esp and loose folders into your Data Files folder. Personally, I'm a MO2 diehard.
All my screenshots were taken with OpenMW, but this will also work with MGE XE, so long as you remember to regenerate your distant land/statics!

Compatibility:
Exteriors - my .esp modifies the references of the non-Arena/Temple cantons to point them to my modified meshes. This shouldn't cause too many compatibility issues, but you'll definitely want to load it below anything else which might be touching the cantons or else it won't work. Anything which outright moves cantons is going to require a patch.

Interiors - this is where compatibility goes to die. Marking an interior as "acts as exterior" causes the game to spawn a plane of water at a fixed elevation, and some of Bethesda's plaza interiors were built below this elevation, meaning I had to move every single object in those plazas so they were no longer underwater. I also had to nudge a few of the interior buildings to reduce clipping. Consequently, any mod-added objects in the plaza interiors could be misplaced. Also, any mods which revert objects (especially door markers!) to their vanilla positions could cause issues. I haven't made any patches, but if you make your own please do share them to save others the effort.

I haven't touched the Arena, so your Arena mods ought to work fine with this.

Technical Details:
This mod adds a new region, "Vivec Cantons Region", which the plazas inherit their weather from. The Vivec Cantons Region is a magical place where it never rains or snows, because Morrowind does not have rain occlusion and nothing destroys uhmershun like rain droplets effortlessly penetrating your glass ceiling. It would also destroy immersion if the interiors and exteriors had noticeably different weather at the same time though, so I've got a few scripts running which make sure that if it's sunny outside, it's sunny inside, and if it's raining outside, it's overcast inside (close enough, right) and so on. Also, if the weather changes while you're inside, the scripts will set the Ascadian Isles Region to have a similar weather when you leave. I am not an experienced Morrowind modder so please let me know if I have stumbled on some bad scripting practice with this.

The domes become more transparent as you get further away because I am doing some bizarre dithering trick to try to force MGE's distant statics to simulate translucency without alpha blending. This is a little distracting if you're vigorously levitating over the city but shouldn't be too obnoxious from the ground level. It might not actually be necessary with OpenMW, but I made this mod before OpenMW had any kind of distant statics, and haven't had a chance to experiment. If anyone knows of a better way to do this, please do feel free to let me know, or, even better, make your own patch to save me the effort.

I am a total Blender amateur so these meshes are GROSS. Being generous I'd call it "Vanilla-styled", since terrible UV mapping and bugs are trademarks of vanilla Morrowind meshes, but honestly it's because I was making it up as I went along. I'd really appreciate it if anyone would like to create improved meshes for this mod.

I actually made this mod months ago and only just got around to uploading it, so I have probably forgotten something important.

Credits:
Atrayonis - I saved a huge amount of time by copying exterior object placement from his mod to create my faux-interiors. Also, his mod inspired this one.
Remiros, Greatness7, Melchior Dark, etc. etc. etc. - My edited meshes are based off of MOP/Project Atlas meshes and textures.
Morrowind Modding Discord - I asked a few questions.
Intelligent Textures - glass texture (but it might get replaced)

To-do:
Fix any bugs.
Meteorite Ministry's trail ought to be visible from the nearby cantons. I may make an addon for that next time I reinstall Morrowind.
Improve meshes and textures.