Area Subdivision Method
Area Subdivision method works in image apace as it is concerned with what is displayed on the screen. It consists of a window in image space and seeks to determine if the window is empty or if the content of the window is the projection of a single visible surface. If not, the window is subdivided into smaller and smaller rectangles or sub-windows until either the content of a sub-window is simple enough to display or the sub-window size is at the limit of the display resolution.
The basic steps of the algorithm can be sequentially listed as follows:
Step1: Initialize the window area to be the whole screen.
Step2: Create a potentially visible polygon (PVPL) with the PVPs sorted on zmin. Place the PVPs in their appropriate categories. Removes hidden by a surrounding polygon and removes disjoint polygons.
Step3: (i) If all polygons are disjoint to the area, set all the pixels to the background colour.
(ii) If PVPL has only a single polygon classified as contained, then fill the area of the window outside the polygon with the background colour, and fill the contained polygon with the appropriate colour.
Step4: If none of the five cases in step3 applies then subdivide the area into fourths. For each subdivided area go to step2.