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