A cup having a safety structure has a cylindrical sidewall and a bottom wall closing a lower end of the sidewall. A predetermined set of attributes are generated to represent a user-defined feature. The trench may include a material of higher refractive index than the waveguide, such as silicon, or alternatively a material having a lower refractive index than the waveguide, such as an air void. The gray-tone features may be implemented as sub-resolution features formed by pixellation. The back illumination component may include a diffuser element disposed under the biological growth plate.