5 Dynamic Visibility Queries

The static visibility relation generally overestimates the visible portion of the model to an observer, since it describes potentially visible portions of the model for a closed, but unlimited set of viewpoints in any direction. The dynamic visibility query is a process of real time determination of visible entities, which is dependent on the current location and viewing direction of the observer. To establish the eye-to-cell visibility we perform a depth first search on the visibility tree, and at each encountered portal we check its incidence with the observer's viewing frustrum (see figure 4). During the eye-to-frustrum visibility query, the DFS is constrained also by the areas of interest induced by encountered portal sequences. Note, that the area of interest corresponds to the antipenumbra on the ``reverse'' side of the portal sequence. Finally, reaching the cell during the cell-to-frustrum visibility, all the objects enclosed inside the frustrum are passed to the rendering subsystem.

Figure 4: Viewing direction dependent pruning of the visibility tree during the dynamic visibility query.

Jiri Bittner - bittner@sgi.felk.cvut.cz