This disclosure describes technology, which can be implemented as a method, apparatus, andor computer software embodied in a computer-readable medium, capable of deforming internal geometry within an outer geometry to account for light bending due to refraction, for example, for real-time modeling of a gaze direction of a 3D computer generated character’s eyes. The preferred embodiments provide a one-piece boot made of a flexible material, such as leather. The pulley alignment apparatus also has a set of gauges for determining the operating position of a variable sheave pulley and determining if a belt is adequate for the variable sheave pulley at the operating position. Playback management information of each of the divided cells and current cell is re-created, and erasion level information is appended to playback management information of the divided cell that belongs to the appending range. A pulse-width modulation signal is generated from the direct current signal based on the control command.