Why does furniture often have a thin, transparent prim underneath it?

[Jennifer Boyle]

The title says it all.

[Ted McGregor]

Not sure, but usually do because ppl tend to sit, walk or rez on top of them so you sit, walk, rez on top of the prim instead of the mesh.

 

It' s more like a marker for the total object, I suppose ?

 

Edited April 27, 2020 by TDD123

[Cindy Evanier]

Its often a shadow

it definitely makes it easier to have a flat root prim/mesh in order to position animations.  Some creators just copy them across to similar furniture I have noticed.  Time saving I guess but leads to some interesting animation positions sometimes.

[Arduenn Schwartzman]

1 hour ago, Jennifer Boyle said:

Why does furniture often have a thin, transparent prim underneath it?

It's usually a mesh square with a bit of shadow texture on it, to give it a bit more depth, especially for people who don't have shadows or ambient occlusion on in their graphics settings.

Like this chair here:

Left has no shadow texture underneath, middle and right do. The right chair is selected in Edit to show the edges of the shadow square.

Edited April 27, 2020 by Arduenn Schwartzman

[Maryanne Solo]

or.... for quietening pixel bottom burps. 🙄

You be the judge. 🤭

[Seicher Rae]

Yeah, no... I know what she's talking about and I've wondered too. It isn't a shadow. I had one little Asian garden building that was littered with the things, just flat, rectangular, transparent 
"prims." When I unlinked everything and removed them, nothing happened except the LI going down. I chalked it up too bad/sloppy design, but wondered what they were doing there. But like the OP said, I have seen this many times on furniture too, for no apparent reason. Since I'm not a builder, I've wondered it this has a purpose and they forgot to remove it.

[Lucia Nightfire]

Some creators use this to show the furniture's animation "footprint" where the scenes will position avatars anywhere within the root prim footprint.

This allows end-users to know how close to put other furniture so any bedside or foot-of-bed scenes don't have avatars standing inside dressers or tables while getting their freak on.

[ChinRey]

2 hours ago, Seicher Rae said:

Yeah, no... I know what she's talking about and I've wondered too. It isn't a shadow. I had one little Asian garden building that was littered with the things, just flat, rectangular, transparent 
"prims." When I unlinked everything and removed them, nothing happened except the LI going down. I chalked it up too bad/sloppy design, but wondered what they were doing there.

Check the creator of the item with and without that prim.

Many, perhaps most, sellers of mesh houses and furniture don't make any mesh themselves, they buy and resell full perm ones. Sometimes they assemble parts from different sources, sometimes they add their own texture but these days it seems it's mostly about reselling fully finished works by somebody else. That of course means that the actul creator shows up as the creator of the object and to avoid that, you add an invisible root prim you made yourself. I suppose the moral/etchical aspect of this is a bit off topic for this thread so let me just say it's not black and white, it's far more complex than that.

Shadow prims/shadow faces is on topic though and I have two comments on that:

• If a piece of funriture has a shadow face, make sure you position it so the shadow is slightly (usually 1-2 cm but be prepared for some trial and error) above the floor. If it's too low, you get texture flickering, if it's to high it's noticeably off.
• The texture resolution for the shadow can be a very good indicator of the maker's technical skills. For a blurry square like the one in Arduenns' picture a good builder will use a 256x256 texture, or even less. Sometimes you need a 512x512 for it but never a 1024x1024. If you happen to come across a 1024 used this way, you can be sure the maker hasn't understood or is ignoring the basics of 3D modelling craftmanship and they're builds will have lots of other hidden flaws too. A few items by builders liek that may still be worth it if they are good designers but if you have lots of that kind of stuff in the same place, you have to expect serious lag issues.

[FairreLilette]

43 minutes ago, ChinRey said:

you add an invisible root prim you made yourself. 

An invisible root prim could be anything or any shape though.  For instance if you turn on transparent (control + alt + t) and look at your own avatar, there are usually odd invisible things floating around your avatar.  If a creator has an invisible root prim under furniture...wouldn't it be more like a shadow they turned transparent?  And, why would a creator turn their root prim shadow to invisble instead of leaving it a shadow?   I'm just wondering because that sounds weird.  The only thing I can think of is they (the creator) didn't like the shadow or object and turned it invisible instead of unlinking it and making it the way they would like it.  

Edited April 27, 2020 by FairreLilette

[ChinRey]

46 minutes ago, FairreLilette said:

And, why would a creator turn their root prim shadow to invisble instead of leaving it a shadow?   I'm just wondering because that sounds weird.

Yes but weird is the normal for SL content.

 

46 minutes ago, FairreLilette said:

The only thing I can think of is they (the creator) didn't like the shadow or object and turned it invisible instead of unlinking it and making it the way they would like it.  

Yes, that's also very possible.

Edited April 27, 2020 by ChinRey

[Lindal Kidd]

It might be transparent simply because it's not intended to be a shadow prim.  Root prims also determine the movement center of an object.  A furniture creator might consider a set of movement axes located at floor level in the center of the chair to be the best location for easy re-positioning.

[HarrisonMcKenzie]

I think shadows are the most common. Aside from looking better, they help you align your furniture properly.

Another possible reason is to add another sit target without just adding a bunch of dummy prims. AVsitter (and I think everything else) requires one prim per avatar. For something like a couch or bench, this is one way to accomplish that without the final product looking dumb.

[Arduenn Schwartzman]

9 minutes ago, HarrisonMcKenzie said:

AVsitter (and I think everything else) requires one prim per avatar.

If it weren't for these large off-sim landscaping megaprims and houses with badly set physics, we'd be able to have single-prim multi-sit furniture in SL.  

Multiple avatars can sit on any object that has been set to 'prim'--unless it is rezzed inside another object, like inside said landscaping objects and houses.

Edited April 29, 2020 by Arduenn Schwartzman

[ChinRey]

16 minutes ago, Arduenn Schwartzman said:

Multiple avatars can sit on any object that has been set to 'prim'--unless it is rezzed inside another object, like inside said landscaping objects and houses.

That's interesting: I always thought the reason why single prim multisit scripts was that they're rather complicated to write. But I tested it and you're right- Not that I ever doubted you of course but seeign is still believing.

That leaves me with a slight problem. I've been working on and off on a multi-sit script trying to figure out a sensible way to juggle animations for multiple avis sitting on the same mesh. But with this limitation I'm wondering if it's worth it or if I should jsut abandon the project.

[Paul Hexem]

13 hours ago, ChinRey said:

That's interesting: I always thought the reason why single prim multisit scripts was that they're rather complicated to write. But I tested it and you're right- Not that I ever doubted you of course but seeign is still believing.

That leaves me with a slight problem. I've been working on and off on a multi-sit script trying to figure out a sensible way to juggle animations for multiple avis sitting on the same mesh. But with this limitation I'm wondering if it's worth it or if I should jsut abandon the project.

Depends on what the script is in. If you think it'll be inside one of those environments, best to plan accordingly. 

[Lindal Kidd]

Wait...you mean my furniture will act differently depending on whether it's outside, or indoors?

[ChinRey]

7 hours ago, Lindal Kidd said:

Wait...you mean my furniture will act differently depending on whether it's outside, or indoors?

Well, if it's outside, it's probably wet from all the rain. That makes quite a bit of differemce.

What Arduenn was talking about though, wasn't houses but bounding boxes. It turns out that if an object is inside another object's bounding box, only one avatar can be seated on it. A bounding box can be much bigger than the object's actual visual and physical shape. There are even some exotic prim twists that push the entire object outside its bounding box (although I do assume there is a mechanism to cope with prims here, is that right, Arduenn?). If the house has three outside walls combined into a signle mesh, the entire house is inside the bounding box of that mesh. If a region has a surround landscape, the entire region is inside its bounding box etc.

Edited April 30, 2020 by ChinRey

[Evah Baxton]

On 4/27/2020 at 11:26 AM, FairreLilette said:

And, why would a creator turn their root prim shadow to invisble instead of leaving it a shadow? 

Turning the shadow on and off is sometimes built into the script. You can control it.

[Jennifer Boyle]

Thanks for all the interesting and informative responses.

Edited May 1, 2020 by Jennifer Boyle
Fixed typo