Area subdivision Method

Area subdivision Method

This hidden surface removal technique is essentially an image space method
But object space operations can be used to accomplish depth ordering of surfaces
Takes advantage of area coherence
Small areas of an image are likely to be covered by only a single polygon

Applied by successively dividing the total view plane into smaller and smaller
rectangles until each rectangle area contains either
The projection of part of a single visible surface
No surface projections
Or the area has been reduced to the size of a pixel
Starting with a total view, apply tests to determine whether area should be subdivided

The basic principle
If the area is sufficiently complex, then subdivide An easy approach is to
Successively divide the area into four equal parts each step
(same as A 1024 x 1024 viewing area could be subdivided ten times
before a subarea is reduced to the size of a single pixel

Four surface classifications
Surrounding surface – Surface completely encloses area
Overlapping surface – Surface partly inside and partly outside
Inside surfac – Surface completely inside
Outside surface – Surface completely outside

No further subdivision required it for specified area one of the following conditions is
true.
Condition 1
Area has no inside, overlapping, or surrounding surfaces (i.e. all surfaces are
outside the area).
Condition 2
Area has only one inside, overlapping, or surrounding surface.
Condition 3
Area has one surrounding surface that obscures all other surfaces within the
area boundaries.