OPCODE/OPC_PlanesAABBOverlap.h

   1 ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
   2 /**
   3  *      Planes-AABB overlap test.
   4  *      - original code by Ville Miettinen, from Umbra/dPVS (released on the GD-Algorithms mailing list)
   5  *      - almost used "as-is", I even left the comments (hence the frustum-related notes)
   6  *
   7  *      \param          center                  [in] box center
   8  *      \param          extents                 [in] box extents
   9  *      \param          out_clip_mask   [out] bitmask for active planes
  10  *      \param          in_clip_mask    [in] bitmask for active planes
  11  *      \return         TRUE if boxes overlap planes
  12  */
  13 ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
  14 inline_ BOOL PlanesCollider::PlanesAABBOverlap(const Point& center, const Point& extents, udword& out_clip_mask, udword in_clip_mask)
  15 {
  16         // Stats
  17         mNbVolumeBVTests++;
  18
  19         const Plane* p = mPlanes;
  20
  21         // Evaluate through all active frustum planes. We determine the relation
  22         // between the AABB and a plane by using the concept of "near" and "far"
  23         // vertices originally described by Zhang (and later by Möller). Our
  24         // variant here uses 3 fabs ops, 6 muls, 7 adds and two floating point
  25         // comparisons per plane. The routine early-exits if the AABB is found
  26         // to be outside any of the planes. The loop also constructs a new output
  27         // clip mask. Most FPUs have a native single-cycle fabsf() operation.
  28
  29         udword Mask                             = 1;                    // current mask index (1,2,4,8,..)
  30         udword TmpOutClipMask   = 0;                    // initialize output clip mask into empty.
  31
  32         while(Mask<=in_clip_mask)                               // keep looping while we have active planes left...
  33         {
  34                 if(in_clip_mask & Mask)                         // if clip plane is active, process it..
  35                 {
  36                         float NP = extents.x*fabsf(p->n.x) + extents.y*fabsf(p->n.y) + extents.z*fabsf(p->n.z); // ### fabsf could be precomputed
  37                         float MP = center.x*p->n.x + center.y*p->n.y + center.z*p->n.z + p->d;
  38
  39                         if(NP < MP)                                             // near vertex behind the clip plane...
  40                                 return FALSE;                           // .. so there is no intersection..
  41                         if((-NP) < MP)                                  // near and far vertices on different sides of plane..
  42                                 TmpOutClipMask |= Mask;         // .. so update the clip mask...
  43                 }
  44                 Mask+=Mask;                                                     // mk = (1<<plane)
  45                 p++;                                                            // advance to next plane
  46         }
  47
  48         out_clip_mask = TmpOutClipMask;                 // copy output value (temp used to resolve aliasing!)
  49         return TRUE;                                                    // indicate that AABB intersects frustum
  50 }