We present a visibility algorithm that is based on sampling the scene for visible surfaces. Each sample represents the portion of geometry that is visible for the lines through that sample's region. Lumping geometry together in grid cells allows achieving visibility at a coarser level, and improves the solution. A rendering algorithm that uses this visibility pre-calculation is presented. Using this method, most hidden geometry is culled and a speedup in rendering time is obtained.
Some problems remain, however, and are discussed here.
Particularly, some cells are left unrendered because they are missed by the discrete sampling procedure, thus potentially creating holes in surfaces. Techniques to improve the solution are proposed. Poulin proposes some reasons why reflection models like Phong's, Blinn's and Cook's are still the most commonly used today even though many other improvements have been introduced. Eurographics '90 award paper. This survey characterizes the various types of shadows.