1. A computer-aided design apparatus ( 2 ) for the design of three-dimensional objects to be fabricated, the apparatus comprising: a base generator operable to generate a plurality of bases in a reference coordinate system, each base comprising a local coordinate system; and a content generator operable to generate a respective content object in the local coordinate system of each of a plurality of bases in accordance with at least one mathematical function having a variable representative of the respective bases in which the content objects are to be located, such that each content object has a shape which depends upon the value of the variable representative of the base in which it is located and such that the shape of the content objects changes from base to base in accordance with the values of the variable.