The Twisted Trees example is really cool. I would not have been able to implement it that well. After playing with it, I think at the most basic the underlying principle is:

> Write your interface as a function of continuous variables, ui = ui(x1,x2,...) = ui(X). When dragging an element, compute the barycentric coordinates λ₁,λ₂,λ₃ of the cursor between the three nearest dropzones. Then render by interpolating the ui parameters between their values at those three dropzones, ui(λ₁X₁ + λ₂X₂ + λ₃X₃).