This operator takes a float input as a bias to blend between three input regions.
The domain of the input is divided into three regions with blurred
boundaries between them. The size (or the contribution) of each region
in the overall domain is given by the two inner boundary inputs
Threshold 1->2 and
Threshold 2->3, which act as region delimiters.
Each inner boundary has an associated blur factor.
A bias value below
thresh12 will pick region1. A value between
thresh23 will pick region2; and a value greater than
thresh23 will pick region3.
The data in each region can be any 1D, 3D, or 4D entity such as color, alpha, position, and so on.