OPC_PlanesAABBOverlap.h

Go to the documentation of this file.

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 Moller). 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
}