What are voxels good for in a Doom-based port?

I keep seeing wishes of people to have voxels in their favourite source ports, and I believe ZDoom already has them (haven't played packs with them though). But what would they be useful for? I understand they can be used to make nice furniture, but that looks to me like eyecandy, not something necessary. Can voxels be used to make gameplay-affecting things such as solid 3D bridges (I'd ask for correct clipping then), and are they easier to add into the software renderer than Quake-like 3D models?

They can be used to replace sprites as well. This is still just a cosmetic change though. I don't know enough about them to know if they can be used for a 3D bridge.
Voxels do work with software renderers better than 3D models since they are pretty much just 3-dimensional sprites, but I have heard that they are harder to use with OpenGL-based ports as a trade-off. I think GZDoom can handle them however.
There is a project to replace item sprites (and switches too for some reason) in DooM with voxels.

printz said:

Can voxels be used to make gameplay-affecting things such as solid 3D bridges (I'd ask for correct clipping then), and are they easier to add into the software renderer than Quake-like 3D models?

No. Voxels are mostly drawn like sprites, ending up as a distinct 2D-like image in the software renderer. So ultimately the have exactly the same limitations.

printz said:

and are they easier to add into the software renderer than Quake-like 3D models?

Probably harder to add voxels when you cannot use code from the Build engine.

Plus there is the clipping (visibility) issue -- Quake relied on a Z-buffer when rendering its 3D models, but Doom software ports don't have that (though you could add one). Though I guess both voxels and 3D models could be clipped in the same was that Doom clips sprites.

Try this for an example of mod which uses them.

You can make small 3D object without having to use portals or 3D floors which will make a mess of the map layout and rendering performances. Things like the Rise of the Triad GADs work well as voxels too.

Large voxel objects tend to have clipping issues.

IMO the best use of voxels is to replace items and decorations. So you don't have the annoying billboard problems. I'm talking about decorations like pillars looking crap when close up, especially with mouselook, items like weapons always facing the player as he strafes and turns around them etc.

With voxels these look like actual 3d objects inside the game world. Oh, I've also seen some switch texture voxels, amazing, they really fit in.

There was an entire branch of ZDoom (or was that GZDoom?) which added voxel support (I don't know if any of the work done there was merged into the mainstream), as well as a burst of activity with people making resources, e.g. pickups and decorations. That was about...uhh dunno, 3-4 years ago?

But, alas, AFAIK it all came apart at the seams when it came to make The One Thing that everybody was hoping for: monsters. And the reason? Just like with HiRes 2D/3D sprite projects: too much work for one person.

Voxel monsters were always a pipe dream, why not use 3D monsters in that case? Voxels aren't good for representing living, moving, animating creatures.

Voxel support is in mainline, most interesting stuff is here I believe, voxel addons for the main games and some popular zdoom mods:

Voxel addons by Voxelbro
http://forum.zdoom.org/viewtopic.php?f=19&t=45526

For Brutal Doom:
Brutal Doom Voxel Patch 2.0
http://forum.zdoom.org/viewtopic.php?f=19&t=47555

VGA said:

IMO the best use of voxels is to replace items and decorations.

This.

To me voxels in Doom nearly always look out of place, similarly to when animators add a few 3D models to otherwise 2D cartoons. Too clashing.

Memfis said:

To me voxels in Doom nearly always look out of place, similarly to when animators add a few 3D models to otherwise 2D cartoons. Too clashing.

Have you checked out Voxelbro's extended Team Hellspawn pack from the link I posted earlier? Last time I checked it out, the items looked great.

Besides, Doom itself may have been planned to use voxel models at some point, with radial symmetry (a radial voxel editor was among Romero's packs o' goodies). The radial approach made sense as models would be trivially drawable with the same column algorithm as pretty much everything else.