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///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
/**
* Planes-AABB overlap test.
* - original code by Ville Miettinen, from Umbra/dPVS (released on the GD-Algorithms mailing list)
* - almost used "as-is", I even left the comments (hence the frustum-related notes)
*
* \param center [in] box center
* \param extents [in] box extents
* \param out_clip_mask [out] bitmask for active planes
* \param in_clip_mask [in] bitmask for active planes
* \return TRUE if boxes overlap planes
*/
///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
inline_ BOOL PlanesCollider::PlanesAABBOverlap(const Point& center, const Point& extents, udword& out_clip_mask, udword in_clip_mask)
{
// Stats
mNbVolumeBVTests++;
const Plane* p = mPlanes;
// Evaluate through all active frustum planes. We determine the relation
// between the AABB and a plane by using the concept of "near" and "far"
// vertices originally described by Zhang (and later by Möller). Our
// variant here uses 3 fabs ops, 6 muls, 7 adds and two floating point
// comparisons per plane. The routine early-exits if the AABB is found
// to be outside any of the planes. The loop also constructs a new output
// clip mask. Most FPUs have a native single-cycle fabsf() operation.
udword Mask = 1; // current mask index (1,2,4,8,..)
udword TmpOutClipMask = 0; // initialize output clip mask into empty.
while(Mask<=in_clip_mask) // keep looping while we have active planes left...
{
if(in_clip_mask & Mask) // if clip plane is active, process it..
{
float NP = extents.x*fabsf(p->n.x) + extents.y*fabsf(p->n.y) + extents.z*fabsf(p->n.z); // ### fabsf could be precomputed
float MP = center.x*p->n.x + center.y*p->n.y + center.z*p->n.z + p->d;
if(NP < MP) // near vertex behind the clip plane...
return FALSE; // .. so there is no intersection..
if((-NP) < MP) // near and far vertices on different sides of plane..
TmpOutClipMask |= Mask; // .. so update the clip mask...
}
Mask+=Mask; // mk = (1<<plane)
p++; // advance to next plane
}
out_clip_mask = TmpOutClipMask; // copy output value (temp used to resolve aliasing!)
return TRUE; // indicate that AABB intersects frustum
}
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