Testing whether objects are of interest within a tile of a 3D computer graphic image

摘要

A display on which a 30 image is to be viewed is subdivided into a plurality of rectangular areas. For each rectangular area a list of objects in the image which may be visible is determined and this is then used to determine how the rectangular area should be shaded for display. In deriving the list of objects a determination of maximum and minimum values for each object in X and Y directions is used and a set of sampling points determined from these values. If a bounding box surrounding the object covers any of the sampling points they are added to the object list or otherwise rejected. Also provided is a method and apparatus for testing edge information for each object against the sample points to determine whether or not the object falls into a rectangular area in a bounding box surrounding the object. The step of testing the edge information includes shifting the edge information by a predetermined amount in dependence of the orientation of each edge.