In general, the method of establishing occlusion of a primitive hidden within a cell is shown in the two examples of FIG. 2E. First, the method establishes that a quadtree cell C, is completely covered e.g., either by a single polygon or by two polygons as illustrated, to obtain a value Czfar for the cell C. With value Czfar then established for this cell C, primitives can then be proven as bein