Performance of scanline algorithms for direct display of CSG

Direct display algorithms display a CSG model without first converting the model into a boundary representation. Three such algorithms are described. All three are based on the scanline display algorithm, and are able to handle both polygonal and quadratic faces.The first algorithm is based on Atherton's recursive subdivision scanline algorithm, the second is a combination of a scanline and a ray casting algorithm, and the third is a scanline version of the Trickle algorithm. A multiprocessor system in which these algorithms can be incorporated is also described.The performances of the algorithms are compared. It turns out that the algorithms efficiently display CSG models on general-purpose architectures. A comparison is also made between the performances for polygon-approximated models and exact models for objects bounded by quadratic faces, such as spherical, cylindrical and conical faces, to get an indication of how many polygons can at most be used to approximate quadratic faces and still have better performance.