The Path-buuer

With a small modi cation the z bu er can be made exi ble enough to be used in global illumination algorithms tra ditionally handled only by ray casting but still enjoy the bene ts of z bu er algorithms including predictable perfor mance memory coherence and acceleration using special ized z bu er hardware The fundamental di erence between the path bu er and a standard z bu er is that the global near clipping plane is replaced with a per pixel near clipping value z The success of each pixel write depends on compares with both the current z and z values We demonstrate the power of this additional test by showing how two global illumination algorithms can be adapted to use the path bu er instead of ray casting First we adapt Kajiya style path tracing for nding view dependent global illumination solutions Since the scene database is streamed through the path bu er and no com plicated meshing or per element storage is needed very large and complex models may be illuminated Both di use and non di use re ectance functions can be handled as well any complex geometric primitives which can be rasterized e g displacement mapped spline surfaces Second we show how the path bu er can be used to do an image gather from a coarse radiosity solution in two pass radiosity methods