Area subdivision method :
It is an example of image space method. The basic principle of this algorithm is to divide are of projection plane into smaller and smaller areas in such a way that each small area belongs to a single surface or no surface at all.
Following are the possible relations of viewing area with surfaces of the scene :-
- Surrounding surface :-> This is the case when surface completely encloses the viewing area.
- Overlapping surface :-> This is the case when overlapping surface is partly inside and partly outside.
- Inside surface :-> The surface is completely inside the area.
- Outside surface :-> Surface is completely outside the area.
Test 2 :-> Only one inside, overlapping or surrounding surface is in the area. This test can also be done by using bounding rectangles in xy plane to identify an inside surface these cases are shown in figure.
If a single inside, overlapping or surrounding surface has been identified, its pixel intensities are transferred to frame buffer. If a single bounding rectangle intersects the area in some way, additional checks are used to determine.
Test 3 :-> A surrounding surface obscures all other surfaces within the area boundaries. This test can be done by two ways :
- Calculate the depth (Z-min, Z-max) for each surface. If for any surface Z-max is greater than Z-min of all other surfaces, then this test is satisfied.
- Find the minimum depth among all the surfaces using plane equations. Surface with minimum depth is the surface when obscures other surfaces.