Run a math operation on one or two vertex groups. Useful for things like merging two vertex groups.
From Object mode, select the objects you want to edit, and go to Object > Apply > Merge Vertex Groups.
The operation should apply to all selected objects it can, which is useful for multi-mesh character rigs.
Or, if you're in Weight Paint Mode, simply go to Weights > Merge Vertex Groups.
This will allow real-time view of the operation if you make changes after applying it.
You can only do one object at a time with this method.
You should get a menu like this:
From here, fill out the names of the desired vertex groups you want to work with. If you want to use a constant, select 'Use Constant' and choose where in the formula you want it to be used. Then set the constant value. The constant value can be any float value--it is not clamped to 0 or 1.
Finally, select your operation. If you want to see what the formula looks like for each one, simply hover your mouse over the option.
Currently, all weight values are clamped to be between 0 and 1. It may be ideal in the future to add an option to normalize the computed outputs instead, so if you had a wide range of values (say 0 to 100), they get remapped to a range of 0 to 1, instead of clamped (and thus essentially ignoring 99% of the value range).
My first vertex group:
Second group:
Simply add the weights together, and done!
To shrink a vertex group, you can subtract the weight of the current group by a constant value. This will remove any vertices with a weight less than the threshold value you supplied. Notice how the weighting for the goo starts a little lower than before.
Afterward, you can normalize the group to get the full range of values again by using Weights > Normalize.
We shrunk the number of vertices in our vertex group, but retained the smoothness on the outer edge,
and also retained the strength of weighting in the primary area.
