Changed: Header inclusion order corrected

[ode.git] / ode / src / collision_util.cpp

/*************************************************************************
 *                                                                       *
 * Open Dynamics Engine, Copyright (C) 2001,2002 Russell L. Smith.       *
 * All rights reserved.  Email: russ@q12.org   Web: www.q12.org          *
 *                                                                       *
 * This library is free software; you can redistribute it and/or         *
 * modify it under the terms of EITHER:                                  *
 *   (1) The GNU Lesser General Public License as published by the Free  *
 *       Software Foundation; either version 2.1 of the License, or (at  *
 *       your option) any later version. The text of the GNU Lesser      *
 *       General Public License is included with this library in the     *
 *       file LICENSE.TXT.                                               *
 *   (2) The BSD-style license that is included with this library in     *
 *       the file LICENSE-BSD.TXT.                                       *
 *                                                                       *
 * This library is distributed in the hope that it will be useful,       *
 * but WITHOUT ANY WARRANTY; without even the implied warranty of        *
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the files    *
 * LICENSE.TXT and LICENSE-BSD.TXT for more details.                     *
 *                                                                       *
 *************************************************************************/

/*

some useful collision utility stuff. this includes some API utility
functions that are defined in the public header files.

*/

#include <ode/common.h>
#include <ode/collision.h>
#include <ode/odemath.h>
#include "config.h"
#include "collision_util.h"

//****************************************************************************

int dCollideSpheres (dVector3 p1, dReal r1,
                     dVector3 p2, dReal r2, dContactGeom *c)
{
  // printf ("d=%.2f  (%.2f %.2f %.2f) (%.2f %.2f %.2f) r1=%.2f r2=%.2f\n",
  //      d,p1[0],p1[1],p1[2],p2[0],p2[1],p2[2],r1,r2);

  dReal d = dCalcPointsDistance3(p1,p2);
  if (d > (r1 + r2)) return 0;
  if (d <= 0) {
    c->pos[0] = p1[0];
    c->pos[1] = p1[1];
    c->pos[2] = p1[2];
    c->normal[0] = 1;
    c->normal[1] = 0;
    c->normal[2] = 0;
    c->depth = r1 + r2;
  }
  else {
    dReal d1 = dRecip (d);
    c->normal[0] = (p1[0]-p2[0])*d1;
    c->normal[1] = (p1[1]-p2[1])*d1;
    c->normal[2] = (p1[2]-p2[2])*d1;
    dReal k = REAL(0.5) * (r2 - r1 - d);
    c->pos[0] = p1[0] + c->normal[0]*k;
    c->pos[1] = p1[1] + c->normal[1]*k;
    c->pos[2] = p1[2] + c->normal[2]*k;
    c->depth = r1 + r2 - d;
  }
  return 1;
}


void dLineClosestApproach (const dVector3 pa, const dVector3 ua,
                           const dVector3 pb, const dVector3 ub,
                           dReal *alpha, dReal *beta)
{
  dVector3 p;
  p[0] = pb[0] - pa[0];
  p[1] = pb[1] - pa[1];
  p[2] = pb[2] - pa[2];
  dReal uaub = dCalcVectorDot3(ua,ub);
  dReal q1 =  dCalcVectorDot3(ua,p);
  dReal q2 = -dCalcVectorDot3(ub,p);
  dReal d = 1-uaub*uaub;
  if (d <= REAL(0.0001)) {
    // @@@ this needs to be made more robust
    *alpha = 0;
    *beta  = 0;
  }
  else {
    d = dRecip(d);
    *alpha = (q1 + uaub*q2)*d;
    *beta  = (uaub*q1 + q2)*d;
  }
}


// given two line segments A and B with endpoints a1-a2 and b1-b2, return the
// points on A and B that are closest to each other (in cp1 and cp2).
// in the case of parallel lines where there are multiple solutions, a
// solution involving the endpoint of at least one line will be returned.
// this will work correctly for zero length lines, e.g. if a1==a2 and/or
// b1==b2.
//
// the algorithm works by applying the voronoi clipping rule to the features
// of the line segments. the three features of each line segment are the two
// endpoints and the line between them. the voronoi clipping rule states that,
// for feature X on line A and feature Y on line B, the closest points PA and
// PB between X and Y are globally the closest points if PA is in V(Y) and
// PB is in V(X), where V(X) is the voronoi region of X.

void dClosestLineSegmentPoints (const dVector3 a1, const dVector3 a2,
                                const dVector3 b1, const dVector3 b2,
                                dVector3 cp1, dVector3 cp2)
{
  dVector3 a1a2,b1b2,a1b1,a1b2,a2b1,a2b2,n;
  dReal la,lb,k,da1,da2,da3,da4,db1,db2,db3,db4,det;

#define SET2(a,b) a[0]=b[0]; a[1]=b[1]; a[2]=b[2];
#define SET3(a,b,op,c) a[0]=b[0] op c[0]; a[1]=b[1] op c[1]; a[2]=b[2] op c[2];

  // check vertex-vertex features

  SET3 (a1a2,a2,-,a1);
  SET3 (b1b2,b2,-,b1);
  SET3 (a1b1,b1,-,a1);
  da1 = dCalcVectorDot3(a1a2,a1b1);
  db1 = dCalcVectorDot3(b1b2,a1b1);
  if (da1 <= 0 && db1 >= 0) {
    SET2 (cp1,a1);
    SET2 (cp2,b1);
    return;
  }

  SET3 (a1b2,b2,-,a1);
  da2 = dCalcVectorDot3(a1a2,a1b2);
  db2 = dCalcVectorDot3(b1b2,a1b2);
  if (da2 <= 0 && db2 <= 0) {
    SET2 (cp1,a1);
    SET2 (cp2,b2);
    return;
  }

  SET3 (a2b1,b1,-,a2);
  da3 = dCalcVectorDot3(a1a2,a2b1);
  db3 = dCalcVectorDot3(b1b2,a2b1);
  if (da3 >= 0 && db3 >= 0) {
    SET2 (cp1,a2);
    SET2 (cp2,b1);
    return;
  }

  SET3 (a2b2,b2,-,a2);
  da4 = dCalcVectorDot3(a1a2,a2b2);
  db4 = dCalcVectorDot3(b1b2,a2b2);
  if (da4 >= 0 && db4 <= 0) {
    SET2 (cp1,a2);
    SET2 (cp2,b2);
    return;
  }

  // check edge-vertex features.
  // if one or both of the lines has zero length, we will never get to here,
  // so we do not have to worry about the following divisions by zero.

  la = dCalcVectorDot3(a1a2,a1a2);
  if (da1 >= 0 && da3 <= 0) {
    k = da1 / la;
    SET3 (n,a1b1,-,k*a1a2);
    if (dCalcVectorDot3(b1b2,n) >= 0) {
      SET3 (cp1,a1,+,k*a1a2);
      SET2 (cp2,b1);
      return;
    }
  }

  if (da2 >= 0 && da4 <= 0) {
    k = da2 / la;
    SET3 (n,a1b2,-,k*a1a2);
    if (dCalcVectorDot3(b1b2,n) <= 0) {
      SET3 (cp1,a1,+,k*a1a2);
      SET2 (cp2,b2);
      return;
    }
  }

  lb = dCalcVectorDot3(b1b2,b1b2);
  if (db1 <= 0 && db2 >= 0) {
    k = -db1 / lb;
    SET3 (n,-a1b1,-,k*b1b2);
    if (dCalcVectorDot3(a1a2,n) >= 0) {
      SET2 (cp1,a1);
      SET3 (cp2,b1,+,k*b1b2);
      return;
    }
  }

  if (db3 <= 0 && db4 >= 0) {
    k = -db3 / lb;
    SET3 (n,-a2b1,-,k*b1b2);
    if (dCalcVectorDot3(a1a2,n) <= 0) {
      SET2 (cp1,a2);
      SET3 (cp2,b1,+,k*b1b2);
      return;
    }
  }

  // it must be edge-edge

  k = dCalcVectorDot3(a1a2,b1b2);
  det = la*lb - k*k;
  if (det <= 0) {
    // this should never happen, but just in case...
    SET2(cp1,a1);
    SET2(cp2,b1);
    return;
  }
  det = dRecip (det);
  dReal alpha = (lb*da1 -  k*db1) * det;
  dReal beta  = ( k*da1 - la*db1) * det;
  SET3 (cp1,a1,+,alpha*a1a2);
  SET3 (cp2,b1,+,beta*b1b2);

# undef SET2
# undef SET3
}


// a simple root finding algorithm is used to find the value of 't' that
// satisfies:
//              d|D(t)|^2/dt = 0
// where:
//              |D(t)| = |p(t)-b(t)|
// where p(t) is a point on the line parameterized by t:
//              p(t) = p1 + t*(p2-p1)
// and b(t) is that same point clipped to the boundary of the box. in box-
// relative coordinates d|D(t)|^2/dt is the sum of three x,y,z components
// each of which looks like this:
//
//          t_lo     /
//            ______/    -->t
//           /     t_hi
//          /
//
// t_lo and t_hi are the t values where the line passes through the planes
// corresponding to the sides of the box. the algorithm computes d|D(t)|^2/dt
// in a piecewise fashion from t=0 to t=1, stopping at the point where
// d|D(t)|^2/dt crosses from negative to positive.

void dClosestLineBoxPoints (const dVector3 p1, const dVector3 p2,
                            const dVector3 c, const dMatrix3 R,
                            const dVector3 side,
                            dVector3 lret, dVector3 bret)
{
  int i;

  // compute the start and delta of the line p1-p2 relative to the box.
  // we will do all subsequent computations in this box-relative coordinate
  // system. we have to do a translation and rotation for each point.
  dVector3 tmp,s,v;
  tmp[0] = p1[0] - c[0];
  tmp[1] = p1[1] - c[1];
  tmp[2] = p1[2] - c[2];
  dMultiply1_331 (s,R,tmp);
  tmp[0] = p2[0] - p1[0];
  tmp[1] = p2[1] - p1[1];
  tmp[2] = p2[2] - p1[2];
  dMultiply1_331 (v,R,tmp);

  // mirror the line so that v has all components >= 0
  dVector3 sign;
  for (i=0; i<3; i++) {
    if (v[i] < 0) {
      s[i] = -s[i];
      v[i] = -v[i];
      sign[i] = -1;
    }
    else sign[i] = 1;
  }

  // compute v^2
  dVector3 v2;
  v2[0] = v[0]*v[0];
  v2[1] = v[1]*v[1];
  v2[2] = v[2]*v[2];

  // compute the half-sides of the box
  dReal h[3];
  h[0] = REAL(0.5) * side[0];
  h[1] = REAL(0.5) * side[1];
  h[2] = REAL(0.5) * side[2];

  // region is -1,0,+1 depending on which side of the box planes each
  // coordinate is on. tanchor is the next t value at which there is a
  // transition, or the last one if there are no more.
  int region[3];
  dReal tanchor[3];

  // Denormals are a problem, because we divide by v[i], and then 
  // multiply that by 0. Alas, infinity times 0 is infinity (!)
  // We also use v2[i], which is v[i] squared. Here's how the epsilons 
  // are chosen:
  // float epsilon = 1.175494e-038 (smallest non-denormal number)
  // double epsilon = 2.225074e-308 (smallest non-denormal number)
  // For single precision, choose an epsilon such that v[i] squared is 
  // not a denormal; this is for performance.
  // For double precision, choose an epsilon such that v[i] is not a 
  // denormal; this is for correctness. (Jon Watte on mailinglist)

#if defined( dSINGLE )
  const dReal tanchor_eps = REAL(1e-19);
#else
  const dReal tanchor_eps = REAL(1e-307);
#endif

  // find the region and tanchor values for p1
  for (i=0; i<3; i++) {
    if (v[i] > tanchor_eps) {
      if (s[i] < -h[i]) {
        region[i] = -1;
        tanchor[i] = (-h[i]-s[i])/v[i];
      }
      else {
        region[i] = (s[i] > h[i]);
        tanchor[i] = (h[i]-s[i])/v[i];
      }
    }
    else {
      region[i] = 0;
      tanchor[i] = 2;           // this will never be a valid tanchor
    }
  }

  // compute d|d|^2/dt for t=0. if it's >= 0 then p1 is the closest point
  dReal t=0;
  dReal dd2dt = 0;
  for (i=0; i<3; i++) dd2dt -= (region[i] ? v2[i] : 0) * tanchor[i];
  if (dd2dt >= 0) goto got_answer;

  do {
    // find the point on the line that is at the next clip plane boundary
    dReal next_t = 1;
    for (i=0; i<3; i++) {
      if (tanchor[i] > t && tanchor[i] < 1 && tanchor[i] < next_t)
        next_t = tanchor[i];
    }

    // compute d|d|^2/dt for the next t
    dReal next_dd2dt = 0;
    for (i=0; i<3; i++) {
      next_dd2dt += (region[i] ? v2[i] : 0) * (next_t - tanchor[i]);
    }

    // if the sign of d|d|^2/dt has changed, solution = the crossover point
    if (next_dd2dt >= 0) {
      dReal m = (next_dd2dt-dd2dt)/(next_t - t);
      t -= dd2dt/m;
      goto got_answer;
    }

    // advance to the next anchor point / region
    for (i=0; i<3; i++) {
      if (tanchor[i] == next_t) {
        tanchor[i] = (h[i]-s[i])/v[i];
        region[i]++;
      }
    }
    t = next_t;
    dd2dt = next_dd2dt;
  }
  while (t < 1);
  t = 1;

  got_answer:

  // compute closest point on the line
  for (i=0; i<3; i++) lret[i] = p1[i] + t*tmp[i];       // note: tmp=p2-p1

  // compute closest point on the box
  for (i=0; i<3; i++) {
    tmp[i] = sign[i] * (s[i] + t*v[i]);
    if (tmp[i] < -h[i]) tmp[i] = -h[i];
    else if (tmp[i] > h[i]) tmp[i] = h[i];
  }
  dMultiply0_331 (s,R,tmp);
  for (i=0; i<3; i++) bret[i] = s[i] + c[i];
}


// given boxes (p1,R1,side1) and (p1,R1,side1), return 1 if they intersect
// or 0 if not.

int dBoxTouchesBox (const dVector3 p1, const dMatrix3 R1,
                    const dVector3 side1, const dVector3 p2,
                    const dMatrix3 R2, const dVector3 side2)
{
  // two boxes are disjoint if (and only if) there is a separating axis
  // perpendicular to a face from one box or perpendicular to an edge from
  // either box. the following tests are derived from:
  //    "OBB Tree: A Hierarchical Structure for Rapid Interference Detection",
  //    S.Gottschalk, M.C.Lin, D.Manocha., Proc of ACM Siggraph 1996.

  // Rij is R1'*R2, i.e. the relative rotation between R1 and R2.
  // Qij is abs(Rij)
  dVector3 p,pp;
  dReal A1,A2,A3,B1,B2,B3,R11,R12,R13,R21,R22,R23,R31,R32,R33,
    Q11,Q12,Q13,Q21,Q22,Q23,Q31,Q32,Q33;

  // get vector from centers of box 1 to box 2, relative to box 1
  p[0] = p2[0] - p1[0];
  p[1] = p2[1] - p1[1];
  p[2] = p2[2] - p1[2];
  dMultiply1_331 (pp,R1,p);             // get pp = p relative to body 1

  // get side lengths / 2
  A1 = side1[0]*REAL(0.5); A2 = side1[1]*REAL(0.5); A3 = side1[2]*REAL(0.5);
  B1 = side2[0]*REAL(0.5); B2 = side2[1]*REAL(0.5); B3 = side2[2]*REAL(0.5);

  // for the following tests, excluding computation of Rij, in the worst case,
  // 15 compares, 60 adds, 81 multiplies, and 24 absolutes.
  // notation: R1=[u1 u2 u3], R2=[v1 v2 v3]

  // separating axis = u1,u2,u3
  R11 = dCalcVectorDot3_44(R1+0,R2+0); R12 = dCalcVectorDot3_44(R1+0,R2+1); R13 = dCalcVectorDot3_44(R1+0,R2+2);
  Q11 = dFabs(R11); Q12 = dFabs(R12); Q13 = dFabs(R13);
  if (dFabs(pp[0]) > (A1 + B1*Q11 + B2*Q12 + B3*Q13)) return 0;
  R21 = dCalcVectorDot3_44(R1+1,R2+0); R22 = dCalcVectorDot3_44(R1+1,R2+1); R23 = dCalcVectorDot3_44(R1+1,R2+2);
  Q21 = dFabs(R21); Q22 = dFabs(R22); Q23 = dFabs(R23);
  if (dFabs(pp[1]) > (A2 + B1*Q21 + B2*Q22 + B3*Q23)) return 0;
  R31 = dCalcVectorDot3_44(R1+2,R2+0); R32 = dCalcVectorDot3_44(R1+2,R2+1); R33 = dCalcVectorDot3_44(R1+2,R2+2);
  Q31 = dFabs(R31); Q32 = dFabs(R32); Q33 = dFabs(R33);
  if (dFabs(pp[2]) > (A3 + B1*Q31 + B2*Q32 + B3*Q33)) return 0;

  // separating axis = v1,v2,v3
  if (dFabs(dCalcVectorDot3_41(R2+0,p)) > (A1*Q11 + A2*Q21 + A3*Q31 + B1)) return 0;
  if (dFabs(dCalcVectorDot3_41(R2+1,p)) > (A1*Q12 + A2*Q22 + A3*Q32 + B2)) return 0;
  if (dFabs(dCalcVectorDot3_41(R2+2,p)) > (A1*Q13 + A2*Q23 + A3*Q33 + B3)) return 0;

  // separating axis = u1 x (v1,v2,v3)
  if (dFabs(pp[2]*R21-pp[1]*R31) > A2*Q31 + A3*Q21 + B2*Q13 + B3*Q12) return 0;
  if (dFabs(pp[2]*R22-pp[1]*R32) > A2*Q32 + A3*Q22 + B1*Q13 + B3*Q11) return 0;
  if (dFabs(pp[2]*R23-pp[1]*R33) > A2*Q33 + A3*Q23 + B1*Q12 + B2*Q11) return 0;

  // separating axis = u2 x (v1,v2,v3)
  if (dFabs(pp[0]*R31-pp[2]*R11) > A1*Q31 + A3*Q11 + B2*Q23 + B3*Q22) return 0;
  if (dFabs(pp[0]*R32-pp[2]*R12) > A1*Q32 + A3*Q12 + B1*Q23 + B3*Q21) return 0;
  if (dFabs(pp[0]*R33-pp[2]*R13) > A1*Q33 + A3*Q13 + B1*Q22 + B2*Q21) return 0;

  // separating axis = u3 x (v1,v2,v3)
  if (dFabs(pp[1]*R11-pp[0]*R21) > A1*Q21 + A2*Q11 + B2*Q33 + B3*Q32) return 0;
  if (dFabs(pp[1]*R12-pp[0]*R22) > A1*Q22 + A2*Q12 + B1*Q33 + B3*Q31) return 0;
  if (dFabs(pp[1]*R13-pp[0]*R23) > A1*Q23 + A2*Q13 + B1*Q32 + B2*Q31) return 0;

  return 1;
}

//****************************************************************************
// other utility functions

void dInfiniteAABB (dxGeom *geom, dReal aabb[6])
{
  aabb[0] = -dInfinity;
  aabb[1] = dInfinity;
  aabb[2] = -dInfinity;
  aabb[3] = dInfinity;
  aabb[4] = -dInfinity;
  aabb[5] = dInfinity;
}


//****************************************************************************
// Helpers for Croteam's collider - by Nguyen Binh

int dClipEdgeToPlane( dVector3 &vEpnt0, dVector3 &vEpnt1, const dVector4& plPlane)
{
        // calculate distance of edge points to plane
        dReal fDistance0 = dPointPlaneDistance(  vEpnt0 ,plPlane );
        dReal fDistance1 = dPointPlaneDistance(  vEpnt1 ,plPlane );

        // if both points are behind the plane
        if ( fDistance0 < 0 && fDistance1 < 0 ) 
        {
                // do nothing
                return 0;
                // if both points in front of the plane
        } 
        else if ( fDistance0 > 0 && fDistance1 > 0 ) 
        {
                // accept them
                return 1;
                // if we have edge/plane intersection
        } else if ((fDistance0 > 0 && fDistance1 < 0) || ( fDistance0 < 0 && fDistance1 > 0)) 
        {

                // find intersection point of edge and plane
                dVector3 vIntersectionPoint;
                vIntersectionPoint[0]= vEpnt0[0]-(vEpnt0[0]-vEpnt1[0])*fDistance0/(fDistance0-fDistance1);
                vIntersectionPoint[1]= vEpnt0[1]-(vEpnt0[1]-vEpnt1[1])*fDistance0/(fDistance0-fDistance1);
                vIntersectionPoint[2]= vEpnt0[2]-(vEpnt0[2]-vEpnt1[2])*fDistance0/(fDistance0-fDistance1);

                // clamp correct edge to intersection point
                if ( fDistance0 < 0 ) 
                {
                        dVector3Copy(vIntersectionPoint,vEpnt0);
                } else 
                {
                        dVector3Copy(vIntersectionPoint,vEpnt1);
                }
                return 1;
        }
        return 1;
}

// clip polygon with plane and generate new polygon points
void             dClipPolyToPlane( const dVector3 avArrayIn[], const int ctIn, 
                                                          dVector3 avArrayOut[], int &ctOut, 
                                                          const dVector4 &plPlane )
{
        // start with no output points
        ctOut = 0;

        int i0 = ctIn-1;

        // for each edge in input polygon
        for (int i1=0; i1<ctIn; i0=i1, i1++) {


                // calculate distance of edge points to plane
                dReal fDistance0 = dPointPlaneDistance(  avArrayIn[i0],plPlane );
                dReal fDistance1 = dPointPlaneDistance(  avArrayIn[i1],plPlane );

                // if first point is in front of plane
                if( fDistance0 >= 0 ) {
                        // emit point
                        avArrayOut[ctOut][0] = avArrayIn[i0][0];
                        avArrayOut[ctOut][1] = avArrayIn[i0][1];
                        avArrayOut[ctOut][2] = avArrayIn[i0][2];
                        ctOut++;
                }

                // if points are on different sides
                if( (fDistance0 > 0 && fDistance1 < 0) || ( fDistance0 < 0 && fDistance1 > 0) ) {

                        // find intersection point of edge and plane
                        dVector3 vIntersectionPoint;
                        vIntersectionPoint[0]= avArrayIn[i0][0] - 
                                (avArrayIn[i0][0]-avArrayIn[i1][0])*fDistance0/(fDistance0-fDistance1);
                        vIntersectionPoint[1]= avArrayIn[i0][1] - 
                                (avArrayIn[i0][1]-avArrayIn[i1][1])*fDistance0/(fDistance0-fDistance1);
                        vIntersectionPoint[2]= avArrayIn[i0][2] - 
                                (avArrayIn[i0][2]-avArrayIn[i1][2])*fDistance0/(fDistance0-fDistance1);

                        // emit intersection point
                        avArrayOut[ctOut][0] = vIntersectionPoint[0];
                        avArrayOut[ctOut][1] = vIntersectionPoint[1];
                        avArrayOut[ctOut][2] = vIntersectionPoint[2];
                        ctOut++;
                }
        }

}

void             dClipPolyToCircle(const dVector3 avArrayIn[], const int ctIn, 
                                                           dVector3 avArrayOut[], int &ctOut, 
                                                           const dVector4 &plPlane ,dReal fRadius)
{
        // start with no output points
        ctOut = 0;

        int i0 = ctIn-1;

        // for each edge in input polygon
        for (int i1=0; i1<ctIn; i0=i1, i1++) 
        {
                // calculate distance of edge points to plane
                dReal fDistance0 = dPointPlaneDistance(  avArrayIn[i0],plPlane );
                dReal fDistance1 = dPointPlaneDistance(  avArrayIn[i1],plPlane );

                // if first point is in front of plane
                if( fDistance0 >= 0 ) 
                {
                        // emit point
                        if (dVector3LengthSquare(avArrayIn[i0]) <= fRadius*fRadius)
                        {
                                avArrayOut[ctOut][0] = avArrayIn[i0][0];
                                avArrayOut[ctOut][1] = avArrayIn[i0][1];
                                avArrayOut[ctOut][2] = avArrayIn[i0][2];
                                ctOut++;
                        }
                }

                // if points are on different sides
                if( (fDistance0 > 0 && fDistance1 < 0) || ( fDistance0 < 0 && fDistance1 > 0) ) 
                {

                        // find intersection point of edge and plane
                        dVector3 vIntersectionPoint;
                        vIntersectionPoint[0]= avArrayIn[i0][0] - 
                                (avArrayIn[i0][0]-avArrayIn[i1][0])*fDistance0/(fDistance0-fDistance1);
                        vIntersectionPoint[1]= avArrayIn[i0][1] - 
                                (avArrayIn[i0][1]-avArrayIn[i1][1])*fDistance0/(fDistance0-fDistance1);
                        vIntersectionPoint[2]= avArrayIn[i0][2] - 
                                (avArrayIn[i0][2]-avArrayIn[i1][2])*fDistance0/(fDistance0-fDistance1);

                        // emit intersection point
                        if (dVector3LengthSquare(avArrayIn[i0]) <= fRadius*fRadius)
                        {
                                avArrayOut[ctOut][0] = vIntersectionPoint[0];
                                avArrayOut[ctOut][1] = vIntersectionPoint[1];
                                avArrayOut[ctOut][2] = vIntersectionPoint[2];
                                ctOut++;
                        }
                }
        }       
}