This part is easier than the last! 😊 We need to make sure that the vertices at the places where the halter top mesh meets other body parts (head, legs) have the same coordinates as those of the head and legs. If not, there can be gaps and weird shadows on the mesh in-game.
In other tutorials, I've seen people use the top view in Milkshape; I use the 3D view, but you can use whichever you're comfortable with.
You've seen it before in screenshots, but make sure the 'top' group is above the group_base one. That is because we will be pulling values from the reference group.
Switch to Wireframe view and unhide the 'top' group. Making sure you're in Select mode, select the two vertices corresponding to the skin, in the middle of the back part of the neck seam, as seen to the left.
What was that? Those aren't two vertices? Not quite! One vertex pertains to the 'top' group, and the other one is part of the seam that connects to the skin of the head.
This is one of those interesting bits I mentioned in the first part. Some clothing items don't have parts that connect "neatly"; in this case, the small border you see around the top actually has the texture of the top, not the skin, and we have to be careful to not accidentally select the outer row of vertices together with the first.
Next we're going to take a look at the Extended Manual Edit panel (which you can find under the Vertex menu). It shows information about the selected vertices - position, bones assigned, normal data - which is very useful. For example, if the normal data isn't identical, you will see dark spots in-game.
Sometimes you can see more than one vertex on some parts of the reference mesh (seen above with the code 0), but in general you will see only one vertex. In any case, everything's fine if all the listed vertices in the reference mesh have the same information (position, normal data). The vertex with code 2 is the one on the group_base group.
Remember the shortcuts we set in the first part? They will help save us a lot of time now. With the vertices selected, press C (Vertex Data Merge) and then press N (Normal Data Merge). You will see the vertices snap into the same place, and pulling up the Extended Manual Edit window will show this:
As you can see, the position and normal data has been copied from the reference vertex, to the one on our mesh!
Now we have to do the same for all the vertices around the neck, pairing the reference ones with the group_base ones.
You can align multiple rows of vertices at the neck - or other areas of the body you're working on - if aligning only the first row of vertices makes the body part look strange. I generally align whatever of the legs is visible, because teen legs are shaped noticeably differently than adult ones. I don't recommend adjusting the arms or hands, as those have a lot of vertices and bones and it's easy to accidentally merge wrong vertices together.
After we're done with that, we move on to the next area: the midriff, where the top connects to the bottom. For this, you will have to zoom in - use Shift+Click-and-drag to zoom in slowly - until you are viewing the vertices from inside the mesh, like below. After this, the procedure is the same as the one above. I've marked which vertices correspond, with the reference mesh once again selected. I recommend pairing up vertices one after the other, either in a clockwise or counter-clockwise direction, otherwise it can be easy to get confused over which you're supposed to pair up, especially if you have multiple vertices in one area.
At this point it is especially important to rotate the mesh occasionally, in order to make sure that you aren't accidentally merging vertices from other parts of the body. It's easy to merge a vertex from the midriff seam to one from the hand or chest, for example, and it's more of a hassle to separate them once merged.
Sometimes - especially when converting from adult to child -, it's possible for the mesh you're working with to have more/fewer vertices at the seams than your reference one. Generally this isn't a problem, as long as you make sure the vertices at the midriff area go inside the body of the sim and there are no gaps between the top and bottom meshes.
After you're done, remember to rotate the mesh around in the viewpoint in Wireframe view and Smooth Shaded view, to check if any of the vertices that are supposed to be inside, have somehow been moved to the outside.
And now that we're done with this, it's time to assign the bones!