1. A method of distributing curvature in a set of target vertices, comprising: obtaining curvature at boundary vertices of the set of target vertices, where curvature is defined using an umbrella operator; and distributing the boundary curvature into the set of target vertices by solving a system of umbrella operator equations for curvatures of respective vertices of the set of target vertices, with the computed curvature at the boundary vertices as a boundary condition for the system of equations.