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<h4 class="subsubsection"> 4.9.8.5 Visibility Culling </h4>
<p>Ok, here it comes. Given the above structure with sectors and entities
we can define how we want to calculate optimal (or near optimal) visibility.
</p>
<p>When speaking about culling we are mainly speaking about three
types of geometry:
</p>
<ul>
<li>
<em>World Geometry</em>
<p>World geometry is the basic geometry that makes up the world.
In general world geometry are big polygons that define large boundaries
in some world or level. They usually represent walls, floors, and
ceilings.
</p>
</li><li>
<em>Detail Objects</em>
<p>Detail objects are entities which are too detailed (i.e. too
many small polygons or triangles) to be included in the processor
intensive visibility calculations. So we mark them as detail and
we process them on a higher level for visibility (mostly by treating
their bounding box instead of the object itself). Curved surfaces,
sprites, and some things are all detail objects.
</p>
</li><li>
<em>Culling Objects</em>
<p>Culling objects are invisible objects. Their only purpose is to cull
geometry. So they are in fact the reverse of detail objects. In general
culling objects should be large and have few polygons. These polygons
will be included in visibility testing. You can add a culling object
inside a detail object. The detail object will not participate in culling
objects behind it (it will itself be culled by its bounding box however)
but the culling object inside will take care of culling what is hidden
by the detail object. Culling objects are only useful for detail objects
that are sufficiently large and in sectors where there is a sufficient
number of other entities (i.e. objects or portals) to be culled.
A question here is whether or not it is possible (easy) to generate culling
objects automatically from detail objects.
</p></li></ul>
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