Proper NetImmerse decal map support
After some discussion it's been made apparent decals need some serious attention. The most pressing problem is we only support one decal slot, when Morrowind.exe can support 8. We don't even handle this single slot correctly.
I'd like to see us move to a modern system for decals and stay away from any multipass solutions, one that doesn't necessarily need a FFP compatibility fallback.
The most common use case for decals right now in Morrowind mods is making use of vertex color alpha or material alpha if none are present to influence the alpha of the decal (blending). More and more mods are making use of this feature, notably OAAB assets.
See more details here: https://github.com/niftools/nifskope/issues/184
Note: I've since edited the scope of this issue, as the original one ran much deeper then I thought.