A Scanline Method for Solid Model Display

The modelling of solid objects is becoming increasingly important in the application of computer graphics to a wide variety of problems, such as CAD/CAM, simulation, and molecular modelling. A variety of methods for rendering solid objects exists, including Z-Buffer, Scanline and Ray Tracing. This paper is concerned with a scanline method for the production of still images of complex objects. The implementation of a scanline algorithm is discussed, in conjunction with a consideration of its performance in relation to the z-buffer method. Many scanline methods cater only for a restricted class of primitives, such as polygons or spheres, whereas this implementation is a general purpose scanline algorithm capable of being extended to handle a variety of primitives. The primitives currently available are polygons, spheres, spheres swept along straight-line trajectories, and cylinders. Polygonal models of cubes, cones and cylinders are also available. The approach is capable of dealing with ``positive'' and ``negative'' volumes, allowing objects with holes to be modelled and displayed. It has further been extended to cater for the inclusion of transparent objects into a scene, and consequently allows the modelling of coloured ``glass'' objects.