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Lets say I have a 3D object that I am weight painting in Blender, but by chance some of the vertices that need to be painted are hidden because of how some areas get weighted more than others. With that being said, is there a way to take what you've weight painted so far and put that into a interactive 2D map of vertices to find which vertices need to be painted and then paint onto that 2D map to help smooth out that specific area.

Can that be done with any of the past or current versions of Blender or is there an addon that allows someone to do as such?

EDIT:

The item in question is rigged, so it does have a shape key.

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  • $\begingroup$ If I got it ... rotate the bone (from rest-pose) that controls complicated area ... you can see immediately which points stay on place (those wasn't painted and now you can access them) or shape deformation is incorrect (wasn't painted enough) ... or is affected by another bone. $\endgroup$
    – vklidu
    Commented Feb 22, 2022 at 18:21

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I've never heard about this kind of feature (it would involve some kind of UV seams and projection), but you can create and activate a shape key, perform the weight painting and delete it when finished.

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  • $\begingroup$ Well, the 3D object in question is rigged which does have a shape key and yes using that does help when the item expands and shrinks to be able to get that finer weight paint detail but it would be a lot easier if it was also done on a flat 2D map as well. In that way it cuts the work flow down quite a bit, if you were looking back and forth from 3D to 2D. $\endgroup$
    – Rami
    Commented Feb 22, 2022 at 9:27
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This is possible. It's not easy, and it's not really a great idea, but I can describe what you need to do, so you can see that for yourself.

So first, we need some way of mapping our 3D vertices to a 2D space-- hey, that's a UV map. So you need a UV map for your mesh, and preferably, one without any overlap.

To create a 2D texture of our existing weights, we can use a quick, throwaway geometry node tree + material:

enter image description here

We can bake that, as non-color emission, to a 2D image of the vertex group specified ("neck" here), and then edit that image using any method we'd like, in Blender, or in Photoshop, or wherever.

When we're done editing that image, we can turn it back into weights on the model by using a pair of vertex weight edit modifiers:

enter image description here

The first vertex weight edit modifier is simple-- we're using a custom curve to set the value of "neck" to zero, everywhere. After that, we're using a second vertex weight edit modifier, modulated by the texture we've baked then edited, to assign all vertices to neck at 1.0, times the value of the texture image.

If we're happy with these weights, we can apply the modifiers. "Modify" type modifiers, like vertex weight edit, are nice in that they can be applied even to meshes with shapekeys.

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