Why do system alpha layers work on some mesh bodies, but not others?

[TheKhajiit]

I've been playing around with the free eBody curvy and a demo of the paid version. Both of them use a BOM relay to bake your skin onto the body. Wearing an alpha layer on the free version does nothing, but on the paid version that alpha will bake onto the body. I understand the free version is probably missing the feature intentionally, but I'm wondering what the mechanics behind this are? I didn't realize alpha could work with BOM at all. I could swear I've been told that it doesn't.

I'm sorry if this question is dumb but I'm still new to mesh.

[Claireschen Hesten]

The BoM relay should work the same on both bodies, i hadn't noticed it working differently to expected on a free version using alt when i tried it. the only limitation on the free version of the body are all HUD based. If you are looking in to getting an eBody do check out the new "Reborn" body it doesn't require a relay to do BoM and has better mainstream, content readily available on the weekend sales circuit support in the the short time it's been out than eBody 'regular' and curvy has ever had

[Rowan Amore]

1 hour ago, TheKhajiit said:

I've been playing around with the free eBody curvy and a demo of the paid version. Both of them use a BOM relay to bake your skin onto the body. Wearing an alpha layer on the free version does nothing, but on the paid version that alpha will bake onto the body. I understand the free version is probably missing the feature intentionally, but I'm wondering what the mechanics behind this are? I didn't realize alpha could work with BOM at all. I could swear I've been told that it doesn't.

I'm sorry if this question is dumb but I'm still new to mesh.

You don't wear an alpha to hide the System body when using a mesh body set to BOM.  You can wear alphas that hide the Mesh BOM body to fit clothing.  I don't know the technical aspects of all this, though.

[Maitimo]

There are three possible alpha settings for the BOM texture on a mesh body -

1) None (no Alpha) - Alpha layers will not work at all.

2) Blended - Alpha layers will work but badly - the body will be invisible beneath any other worn alpha such as lacy clothes or long hair

3) Masked - the only correct setting. Alpha layers will work, no conflict with other alpha items. 

If the body is Mod (such as Kalhene Erika or the updated Belleza bodies, the user can change this themselves. If no-mod, it cannot be changed.

Ebody uses setting 1 (none) on its free bodies, and they are no-mod, so if you want to use alpha layers, you will need to pay for a body that uses setting 3. 

Edited November 22, 2021 by Maitimo

[Jenna Huntsman]

33 minutes ago, Maitimo said:

2) Blended - Alpha layers will work but badly - the body will be invisible beneath any other worn alpha such as lacy clothes or long hair

To add on to this part,

If your body is using Blending as it's mask mode, if you wear a full body alpha, the mesh will not disappear, instead it turns red (at least, in some cases - not all).

Edited November 22, 2021 by Jenna Huntsman

[Nalates Urriah]

OMG... there is so much confusion. I suppose I should add my part.

Mesh bodies are prims. They allow all the attributes you find in the Build Panel. They are rendered in the part of the render pipeline made for prims. The avatar body is rendered by a different part of the pipeline design specifically for avatars. Alpha works only as a system layer for the classic body. Avatars are the only thing in SL that have multiple texture layers.

Prims have a Diffuse, Normal, and Specular (aka: texture/color, bump map, shiny map - again aka Materials) layer on every face. The build editor allows one to set any prim face to a range of transparency, 0 to 100%. But prims have no alpha mask capability. Designers build transparency into the color layer. it is this transparency that has Blending Modes; blending, masking, and emissive. The classic avatar body has none of these attributes.

If you put a clear texture on a prim, you can see through the prim. Its like glass. With the avatar a clear texture does not make it clear. To do that we add a black and white image into an Alpha Layer (which is a system layer) which acts like a mask and hides part of the body. Originally, before mesh bodies, this was how avatars were made to work with clothes.

Along come mesh bodies and BOM. The result is a cross-bred render using parts of both render pipelines, which I think is why there is so much confusion. The Lindens realized in development of BOM that this was going to confuse people. So, they put in an anti-gotcha feature to help out. If you alpha out the entire head, upper, and/or lower body and wear BOM you get a warning, the red, yellow, and blue BOM textures.

Once the SL system detects a BOM enabled prim, aka mesh body, it uses the layers of the avatar classic body, including alphas, to bake textures for the mesh body. Enabling BOM simply tells the system to use the texture coming from the bake engine for the enabled prim. The bake engine makes transparent the the parts of the mesh body alpha'd out on the classic body. Said another way, it makes parts of the Diffuse (aka texture/color) layer clear, transparent according to the classic body's alpha layers.

Thought of another way... the BOM Mesh body duplicates what you have done on the Classic body. If the BOM body doesn't look right, take it off and make the Classic body look right then put the BOM Mesh body back on.

When thing go wrong it is always because we have messed up because we have confused where we are doing what.

[Stephanie Misfit]

On this topic, alpha layers don't work on the Belleza body for me when I wear it straight out of the box. I have the updated BOM version. Anyone know how to get them to work, i.e. where the specific setting is in the HUD? Thanks.

[steeljane42]

15 minutes ago, Stephanie Misfit said:

On this topic, alpha layers don't work on the Belleza body for me when I wear it straight out of the box. I have the updated BOM version. Anyone know how to get them to work, i.e. where the specific setting is in the HUD? Thanks.

Skin's part of the HUD on top left where it says BoM; click right to it (probably says None right now). It swaps alpha mode between none, mask and blend.

Edited November 22, 2021 by steeljane42