postCull callbacks aren't being called

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David Luebke (luebke++at++cs.unc.edu)
Wed, 19 Apr 1995 04:13:18 -0400 (EDT)

I'm implementing run-time cell-portal visibility in Performer. Here's the
idea: the scene is divided into adjacent cells, which can only see each
other through transparent portals that connect the cells. At the root of the
scene is the pfGroup containing the viewer's cell. Under that cell are
the portals of the cell, which I've implemented as pfGroups with pre-
and post-callbacks attached. The precallback is called preCullPortal;
it tests to see if the portal is visible; if so, the callback attaches
the cell on the other side to the portal pfGroup with pfAddChild(), and
returns PFTRAV_CONT. PostCullPortal() is responsible for removing the
attached cell from the pfGroup that represents the portal.

So here's my problem: after a nested series of prePortalCull() calls,
postPortalCull() seems to be called only once, for the most recently
visited portal node. As a result the cells attached to the rest of the
portals never get removed, and those portals thereby inherit another
child each frame. My question is, why might the traversal mechanism
be skipping every postPortalCull after the first call? I've checked
carefully and I'm quite sure that the correct callbacks are assigned
to all the appropriate nodes. Any ideas?

I know this probably isn't very clear. Here's the relevant portions of
my code:

typedef struct
{
    int numverts; /* Number of verts in the portal */
    pfGroup *attached_cell; /* cell on the 'other side' */
    pfVec3 verts[MAXPORTALVERTS]; /* The actual vertices */
} pfPortalData;

long
enterPortalCull(pfTraverser *trav, void *data)
{
    pfChannel *chan; /* pfChannel derives from pfFrustum */
    pfGroup *node;
    pfPortalData *p = (pfPortalData *) data;
     
    if (!globalUsePortals) /* First, are portals enabled? */
    {
        DEBUG(("\tPortals aren't enabled; pruning.\n"));
        return PFTRAV_PRUNE;
    }
    node = (pfGroup *) pfGetTravNode(trav);

    chan = pfGetTravChan(trav); /* Get the current view frustum */
    if (chan == NULL) /* If this is an intersection, prune */
    {
        return PFTRAV_PRUNE;
    }
    ...
    /* First test the normal of the portal to see if its backfacing */
    ...
    /* Next test the portal to see if its visible */
    ...
    if (it's not visible)
        return PFTRAV_PRUNE;

    /* It's visible, go ahead and traverse the other side */
    pfAddChild(node, p->attached_cell);
    return PFTRAV_CONT;
}

long
exitPortalCull(pfTraverser *trav, void *data)
{
    pfPortalData *p = (pfPortalData *) data;
    pfChannel *chan;
    pfGroup *node;

    if (!globalUsePortals) /* First, are portals enabled? */
        return PFTRAV_PRUNE; /* I think this is ignored */

    chan = pfGetTravChan(trav); /* Get the current view frustum */
    node = (pfGroup *) pfGetTravNode(trav);

    if (chan == NULL) /* If this is an intersection, prune */
        return PFTRAV_PRUNE; /* I think this is ignored */

    pfRemoveChild(node, p->attached_cell);
    return PFTRAV_CONT; /* I think this is ignored */
}

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