Things you need to know about mesh bodies (Part 1)

This article was published in Fusion Magazine, February 2015. Click for the magazine!

Who hasn't heard about mesh bodies nowadays? Like mesh hands and feet did before, they improve the appearance of our avatar, making it quite smoother than the default SL avatar. If you're interested in acquiring one, or even if you already have purchased one (or more than one), this mini series will clarify a few key concepts.

Daily, I see questions about what can/cannot be done with mesh bodies, or wondering if scripts could do things to them that are simply not possible. I also see questions about appliers, and particularly, the Omega applier. My goal is to take the mystery out of all this.

First of all: What is a mesh body? Technically, a mesh body is a set of linked SL primitives of mesh type, containing data about the geometry defining it, how this geometry should conform to the SL avatar and changes in some sliders (rigged mesh), and the textures to be applied.

It is important to realize that mesh objects, no matter how complex their geometry, are still seen as fancy boxes by the server, fancy boxes that have several faces that can be easily textured by scripts.

Figure 1. This is a mesh body too. Not so fancy, but it illustrates the idea of several linked objects and faces that can be textured
Also, mesh bodies are made of more pieces than the very simple concept shown in the picture. One of the reasons is because of the alpha zones and the fact that each mesh primitive may have up to eight different faces to be textured. If a ninth face is needed, then another mesh primitive has to be used. But let's not confuse ourselves with this yet.

Before that, let's talk about the naked skin shown on a mesh body. Later in the series we will get into clothing and the alpha zones.

Within the modelling program, whether this is Blender or others, we have several ways to texture a mesh. But because this mesh will be later exported and uploaded to SL, the mesh needs to be unwrapped. What does this mean? It means that we have to lay flat our mesh object (so textures can be created), creating a map, or guides if you will, indicating which point of the mesh will be textured by which pixel of the texture.

In order to create a texture that will fit that mesh object, we have to use these guides, painting by following its shape. We may hear that those guides are the UVs of the mesh object. It's good to be familiarized with the general idea: The UV of a mesh can be understood as the guides used to paint the texture. Of course, this is a very simplistic explanation of the term UV, but remember: the purpose of this mini series is understanding some basic concepts. We don't need to know all the technical details in order to learn what can be achieved with mesh bodies, and what cannot be.

Each creator of a mesh body could use their own UV if they wanted to. But this would be a nightmare for skin creators that create skin appliers, to begin with. Suppose that we have three different mesh bodies, and three different UVs for them, as this picture shows:

Figure 2. Three different arrangements of UVs done with Makehuman
Now, suppose you're a skin creator, you have ten skin tones, and you want to offer appliers for the three mesh bodies, so your customers can purchase the appliers that fit with their body. This means that you should work the ten tones over three different UV configurations. It sounds like a lot of work!

Instead of this, what mesh body creators do (at least, the creators of the four mesh bodies I've tried), is to unwrap their mesh bodies so they conform to an already known UV that saves a lot of work to skin and clothes creators. This UV is the UV of... the default SL avatar.

Figure 3. The UVs of the SL avatar upper and lower body
Still, making skin appliers is no click and go. Each mesh body has their own appliers system, which means creating a different set of HUDs per body, and skin creators could also need to retouch the tones of their skins, fix mistakes, then upload them again.

Actually, when I've said "at least, the creators of the four mesh bodies I've tried", that wasn't 100% accurate. There's a mesh body from the four I've tried, Belleza Venus, which has different UVs for hands and feet than the UVs of the SL avatar. This means that skin creators making appliers for the Venus body, have to redo the textures of their hands and feet, in all the tones they consider they will be supporting. This may also have consequences for clothes creators making appliers for this body.

We will continue in the next issue, but before closing this first part, I'd like to point one consequence of all we've explained here.

We've pointed out that some body parts, like the Belleza Venus hands and feet, do not conform to the UV of the SL avatar. There is no script solution for this. A script cannot magically transform one texture conforming one UV, to a different texture conforming another UV. A script can apply a texture onto the faces of a mesh. And that's it. The texture needs to exist. This means, the creator has to create and upload it.

This is why not conforming to the UV of the SL avatar is a bad idea. There's already a lot of work to do creating appliers for all the systems and brands a creator decides to support. Giving them more work than necessary is not a good idea.

Now, yes... See you in the next issue! Enjoy your SL.