Determine in brief the Painter Algorithm

a) The farthest polygon, namely the rectangle PQRS, is stored first.

(b) The next farthest, the quadrilateral ABCD, is superposed, covering the  portion PQUT of the rectangle and leaving visible the portion TURS of the rectangle.

(c) Finally the closest, namely the triangle EFG, is superposed, entirely within the quadrilateral, and covering it in the region EFG.

The primary requirement for this algorithm is the sorting of polygons by priority, depending on whether a polygon covers (or is covered by) another polygon partly or wholly. This determination is made by comparing the x-, y-, and z-extents of the various polygons.

In case the z-extents of any two polygons overlap, then, if the two polygon planes are parallel to each other there is obscuring of one by the other; if the two polygon planes are not parallel, they may intersect each other. In such cases, the covered/uncovered or penetrated invisible/visible portions are determined by geometrical and clipping procedures, including the determination of the line of intersection of the two polygons if necessary, and separated into independent regions.