1. Dynamic Graphics Project, CSRI, University of Toronto, Toronto, Ontario, Canada M5S 1A4 and Alias/Wavefront, 110 Richmond St. East, Toronto, Ontario, Canada M5C 1P1
2. Alias/Wavefront, 110 Richmond St. East, Toronto, Ontario, Canada M5C 1P1 and Dynamic Graphics Project, CSRI, University of Toronto, Toronto, Ontario, Canada M5S 1A4