An enhanced treatment of hidden lines

A new display scheme is presented in which three-dimensional objects are represented with a much higher degree of user control of the line-drawing format than those in conventional schemes. In this scheme, the attribute of a line is determined not at the time of definition but after the viewing transformation has been applied, taking the shielding environment of the line into consideration. The essential difference between our scheme and conventional hidden-line removal/indication lies in the treatment of the shielding environment. In conventional hidden-line removal/indication, only the visible/invisible information is available for the selection of the attribute of a line. In our scheme, the entire set of surfaces that hide a line can be used to determine the attribute of the line. A much higher degree of freedom in generating pictures is achieved owing to the treatment of the shielding environment. We also describe a system called GRIP, which implements the new scheme.