1. A method for manipulating computer-generated objects in a computer-generated scene, the method comprising: receiving, at one or more computer systems, information specifying a first object in the computer-generated scene, the first object forming a boundary; receiving, at the one or more computer systems, information specifying a second object in the computer-generated scene, the second object located at least in part within the boundary formed by the first object; determining, with one or more processors associated with the one or more computer systems, generalized barycentric coordinates for a first location located within the boundary based on position of one or more selected locations on the boundary and position of one or more selected locations on the part of the second object located within the boundary; interpolating, with the one or more processors associated with the one or more computer systems, at least one value for the first location based on the determined generalized barycentric coordinates for the first location; and storing, in a storage device associated with the one or more computer systems, information associated with the at least one interpolated value for the first location.