1. A computer-implemented method, comprising: obtaining a surface patch, wherein the surface patch represents a surface as an N-sided patch including one or more internal constraint curves; receiving input selecting at least one of the internal constraint curves; in response to said input selecting at least one of the internal constraint curves, generating a separate internal N-sided patch from each selected internal constraint curve with the selected internal constraint curve as an external boundary of the internal patch; and displaying the surface as the surface patch including the at least one internal patches, wherein the surface patch and each of the at least one internal patches are each configured to be separately modified to affect the displayed surface.