A method is provided to model a 3D structure comprising: producing a surface mesh representation of the 3D structure； producing a volume mesh representation of the 3D structure based upon the surface mesh； sorting vertices of the volume mesh into a first sub-list that includes only surface vertices and a second sub-list that includes only internal vertices； applying shading to the surface mesh by accessing only surface vertices in the first sub-list； determining deformation of the volume mesh by accessing both surface vertices in the first sub-list and internal vertices in the second sub-list.
