Bodygroups have lighting issues in Playermodels compared to original

[Grodbert]

I'm back with a "new" problem, not really new because I already made a post about this but it got no attention, I'll keep it short, constantly, when I make a playermodel using an existing ragdoll all of the bodygroups stand out instead of blending in like in the original addon, this doesn't make sense because the textures are the same, same with the model, and it's not an isolated case since similar playermodels in the workshop have the same problem, the image below is all you need to see, left picture is the original ragdoll from Yunpol's generation 5 pokemon and the right picture is my playermodel, you can notice the bodygroups easily, the eyes:

If you had a similar issue and resolved it, please respond.

[Sundownsyndrome]

if you're desperate you can try and weld the vertices together, or merge them. whatever you do in blender, i'm not sure - but there's an equivalent i know of. try that and then adjust the smoothing splits. see if that works.

[ubre]

[Grodbert]

I already tried that long time ago, only thing I can do is just merge the 2 and use different skins instead of bodygroups, which is probably what I'll do with simpler models, doing what you told me will just undo itself or screw up all the normals when I separate the 2 models again.

[Flaming Neko]

I'd like to know how to fix this through Blender, if possible.

I did this once, but it involved grabbing the normals from a merged body.smd in Notepad++ and pasting the respective stuff into the eyes.smd - annoying.

[Grodbert]

Ubre's video was really helpful, but if you don't have the time I'll just explain, the bug is caused when you decompile the mdl or when you export it from blender (don't know which).
The vertex normals are aligned when you create the bodygroups for the first time, however when you try to modify the mesh or even view it, the vertex normals change, creating that god awful effect.
The best way to fix this problem is to just (in blender) merge them together so they're one mesh (with no cuts) using the bridge edge loop tool, then you separate the eyes from the mesh again by splitting the vertices with V , when you save them as different .smd they will align perfectly with no lightning error.
Just make sure not to open the file again, it's the shrodinger's mesh, it's both broken and fixed until you open the file.

[Flaming Neko]

I can't get this to work for some reason. I merge the eyes with the body using the 'Bridge Edge Loops" tool (with merge enabled), so far it's smooth, but soon as I hit 'V' to separate the eyes I'm back to square one.
Not sure what I'm doing wrong here!

[Grodbert]

Once merged, try selecting the eyes, press P and do "separate by selection".
If that too didn't work I used to use a horrible workaround that I suggest you never use, it consists on duplicating the nearest faces of the body and merging them to the bodygroup so the vertex normals would be forced to be as if they were connected, then apply an invisible material to the extra duplicated parts, but this can ruin the mesh so I stopped using it.

[Flaming Neko]

Sadly, this didn't work either. I'm not sure if I have to do something specific. A shame, because this would make it much more simpler.

I found one method that works, though.
Duplicate the eyes and body for later.
Join the eyes and the body together and weld the seams (Remove Double works here). We'll need this as a reference for a Modifier.
Leave the merged mesh alone and apply the 'Data Transfer' Modifier on both the eyes and the body mesh. Select the merged mesh as reference, check the 'Face Corner Data' along with 'Custom Normals' below it, select 'Nearest Corner of Nearest Face' in the dropdown menu.
Head over to 'Object Data' and select 'Auto Smooth' so that the Normals get transferred over.
The edges around the seperated mesh should be smooth now.
This works well, but Auto Smooth recalculates the rest of the mesh too, so if something is not marked as sharp, it becomes smooth, I think.