4.6 The Drawing Pass 297
cease to use depth-first search for the traversal. The traversal path is based on the
visibility graph implied by the room-portal graph. One of the performance issues in
a portal system is overdraw of the contents of a room because multiple portals lead
into the room and the camera/observer can see through both portals from a single
location. To avoid this, a class derived from
Culler may be used for the portal system.
It accumulates the potentially visible objects during the traversal of the room-portal
graph but maintains a set of unique objects; that is, an object is never added twice to
the set.
4.6 The Drawing Pass
The input to a culling pass is a scene graph. The output is a potentially visible set of
objects. This set