/*************************************************************************
 *                                                                       *
 * 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 "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 = dDISTANCE (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] = dMUL((p1[0]-p2[0]),d1);
    c->normal[1] = dMUL((p1[1]-p2[1]),d1);
    c->normal[2] = dMUL((p1[2]-p2[2]),d1);
    dReal k = dMUL(REAL(0.5),(r2 - r1 - d));
    c->pos[0] = p1[0] + dMUL(c->normal[0],k);
    c->pos[1] = p1[1] + dMUL(c->normal[1],k);
    c->pos[2] = p1[2] + dMUL(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 = dDOT(ua,ub);
  dReal q1 =  dDOT(ua,p);
  dReal q2 = -dDOT(ub,p);
  dReal d = 1-dMUL(uaub,uaub);
  if (d <= REAL(0.0001)) {
    // @@@ this needs to be made more robust
    *alpha = 0;
    *beta  = 0;
  }
  else {
    d = dRecip(d);
    *alpha = dMUL((q1 + dMUL(uaub,q2)),d);
    *beta  = dMUL((dMUL(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.

EXPORT_C 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 = dDOT(a1a2,a1b1);
  db1 = dDOT(b1b2,a1b1);
  if (da1 <= 0 && db1 >= 0) {
    SET2 (cp1,a1);
    SET2 (cp2,b1);
    return;
  }

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

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

  SET3 (a2b2,b2,-,a2);
  da4 = dDOT(a1a2,a2b2);
  db4 = dDOT(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 = dDOT(a1a2,a1a2);
  if (da1 >= 0 && da3 <= 0) {
    k = dDIV(da1,la);
    a1a2[0] = dMUL(k,a1a2[0]);
    a1a2[1] = dMUL(k,a1a2[1]);
    a1a2[2] = dMUL(k,a1a2[2]);
    SET3 (n,a1b1,-,a1a2);
    if (dDOT(b1b2,n) >= 0) {
      a1a2[0] = dMUL(k,a1a2[0]);
      a1a2[1] = dMUL(k,a1a2[1]);
      a1a2[2] = dMUL(k,a1a2[2]);
      SET3 (cp1,a1,+,a1a2);
      SET2 (cp2,b1);
      return;
    }
  }

  if (da2 >= 0 && da4 <= 0) {
    k = dDIV(da2,la);
    a1a2[0] = dMUL(k,a1a2[0]);
    a1a2[1] = dMUL(k,a1a2[1]);
    a1a2[2] = dMUL(k,a1a2[2]);
    SET3 (n,a1b2,-,a1a2);
    if (dDOT(b1b2,n) <= 0) {
      a1a2[0] = dMUL(k,a1a2[0]);
      a1a2[1] = dMUL(k,a1a2[1]);
      a1a2[2] = dMUL(k,a1a2[2]);
      SET3 (cp1,a1,+,a1a2);
      SET2 (cp2,b2);
      return;
    }
  }

  lb = dDOT(b1b2,b1b2);
  if (db1 <= 0 && db2 >= 0) {
    k = -dDIV(db1,lb);
    b1b2[0] = dMUL(k,b1b2[0]);
    b1b2[1] = dMUL(k,b1b2[1]);
    b1b2[2] = dMUL(k,b1b2[2]);
    SET3 (n,-a1b1,-,b1b2);
    if (dDOT(a1a2,n) >= 0) {
      b1b2[0] = dMUL(k,b1b2[0]);
      b1b2[1] = dMUL(k,b1b2[1]);
      b1b2[2] = dMUL(k,b1b2[2]);
      SET2 (cp1,a1);
      SET3 (cp2,b1,+,b1b2);
      return;
    }
  }

  if (db3 <= 0 && db4 >= 0) {
    k = -dDIV(db3,lb);
    b1b2[0] = dMUL(k,b1b2[0]);
    b1b2[1] = dMUL(k,b1b2[1]);
    b1b2[2] = dMUL(k,b1b2[2]);
    SET3 (n,-a2b1,-,b1b2);
    if (dDOT(a1a2,n) <= 0) {
      b1b2[0] = dMUL(k,b1b2[0]);
      b1b2[1] = dMUL(k,b1b2[1]);
      b1b2[2] = dMUL(k,b1b2[2]);
      SET2 (cp1,a2);
      SET3 (cp2,b1,+,b1b2);
      return;
    }
  }

  // it must be edge-edge

  k = dDOT(a1a2,b1b2);
  det = dMUL(la,lb) - dMUL(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 = dMUL((dMUL(lb,da1) -  dMUL(k,db1)),det);
  a1a2[0] = dMUL(alpha,a1a2[0]);
  a1a2[1] = dMUL(alpha,a1a2[1]);
  a1a2[2] = dMUL(alpha,a1a2[2]);
  dReal beta  = dMUL(( dMUL(k,da1) - dMUL(la,db1)),det);
  b1b2[0] = dMUL(beta,b1b2[0]);
  b1b2[1] = dMUL(beta,b1b2[1]);
  b1b2[2] = dMUL(beta,b1b2[2]);
  SET3 (cp1,a1,+,a1a2);
  SET3 (cp2,b1,+,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] = REAL(-1.0);
    }
    else sign[i] = REAL(1.0);
  }

  // compute v^2
  dVector3 v2;
  v2[0] = dMUL(v[0],v[0]);
  v2[1] = dMUL(v[1],v[1]);
  v2[2] = dMUL(v[2],v[2]);

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

  const dReal tanchor_eps = REAL(2e-5f);

  // 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] = dDIV((-h[i]-s[i]),v[i]);
      }
      else {
	region[i] = (s[i] > h[i]);
	tanchor[i] = dDIV((h[i]-s[i]),v[i]);
      }
    }
    else {
      region[i] = 0;
      tanchor[i] = REAL(2.0);		// 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 -= dMUL((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 = REAL(1.0);
    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 = REAL(0.0);
    for (i=0; i<3; i++) {
      next_dd2dt += dMUL((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 = dDIV((next_dd2dt-dd2dt),(next_t - t));
      t -= dDIV(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] = dDIV((h[i]-s[i]),v[i]);
	region[i]++;
      }
    }
    t = next_t;
    dd2dt = next_dd2dt;
  }
  while (t < REAL(1.0));
  t = REAL(1.0);

  got_answer:

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

  // compute closest point on the box
  for (i=0; i<3; i++) {
    tmp[i] = dMUL(sign[i],(s[i] + dMUL(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.

EXPORT_C 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 = dMUL(side1[0],REAL(0.5)); A2 = dMUL(side1[1],REAL(0.5)); A3 = dMUL(side1[2],REAL(0.5));
  B1 = dMUL(side2[0],REAL(0.5)); B2 = dMUL(side2[1],REAL(0.5)); B3 = dMUL(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 = dDOT44(R1+0,R2+0); R12 = dDOT44(R1+0,R2+1); R13 = dDOT44(R1+0,R2+2);
  Q11 = dFabs(R11); Q12 = dFabs(R12); Q13 = dFabs(R13);
  if (dFabs(pp[0]) > (A1 + dMUL(B1,Q11) + dMUL(B2,Q12) + dMUL(B3,Q13))) return 0;
  R21 = dDOT44(R1+1,R2+0); R22 = dDOT44(R1+1,R2+1); R23 = dDOT44(R1+1,R2+2);
  Q21 = dFabs(R21); Q22 = dFabs(R22); Q23 = dFabs(R23);
  if (dFabs(pp[1]) > (A2 + dMUL(B1,Q21) + dMUL(B2,Q22) + dMUL(B3,Q23))) return 0;
  R31 = dDOT44(R1+2,R2+0); R32 = dDOT44(R1+2,R2+1); R33 = dDOT44(R1+2,R2+2);
  Q31 = dFabs(R31); Q32 = dFabs(R32); Q33 = dFabs(R33);
  if (dFabs(pp[2]) > (A3 + dMUL(B1,Q31) + dMUL(B2,Q32) + dMUL(B3,Q33))) return 0;

  // separating axis = v1,v2,v3
  if (dFabs(dDOT41(R2+0,p)) > (dMUL(A1,Q11) + dMUL(A2,Q21) + dMUL(A3,Q31) + B1)) return 0;
  if (dFabs(dDOT41(R2+1,p)) > (dMUL(A1,Q12) + dMUL(A2,Q22) + dMUL(A3,Q32) + B2)) return 0;
  if (dFabs(dDOT41(R2+2,p)) > (dMUL(A1,Q13) + dMUL(A2,Q23) + dMUL(A3,Q33) + B3)) return 0;

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

  // separating axis = u2 x (v1,v2,v3)
  if (dFabs(dMUL(pp[0],R31)-dMUL(pp[2],R11)) > dMUL(A1,Q31) + dMUL(A3,Q11) + dMUL(B2,Q23) + dMUL(B3,Q22)) return 0;
  if (dFabs(dMUL(pp[0],R32)-dMUL(pp[2],R12)) > dMUL(A1,Q32) + dMUL(A3,Q12) + dMUL(B1,Q23) + dMUL(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(dMUL(pp[1],R11)-dMUL(pp[0],R21)) > dMUL(A1,Q21) + dMUL(A2,Q11) + dMUL(B2,Q33) + dMUL(B3,Q32)) return 0;
  if (dFabs(dMUL(pp[1],R12)-dMUL(pp[0],R22)) > dMUL(A1,Q22) + dMUL(A2,Q12) + dMUL(B1,Q33) + dMUL(B3,Q31)) return 0;
  if (dFabs(dMUL(pp[1],R13)-dMUL(pp[0],R23)) > dMUL(A1,Q23) + dMUL(A2,Q13) + dMUL(B1,Q32) + dMUL(B2,Q31)) return 0;

  return 1;
}

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

EXPORT_C 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]-dMUL((vEpnt0[0]-vEpnt1[0]),dDIV(fDistance0,(fDistance0-fDistance1)));
		vIntersectionPoint[1]= vEpnt0[1]-dMUL((vEpnt0[1]-vEpnt1[1]),dDIV(fDistance0,(fDistance0-fDistance1)));
		vIntersectionPoint[2]= vEpnt0[2]-dMUL((vEpnt0[2]-vEpnt1[2]),dDIV(fDistance0,(fDistance0-fDistance1)));

		// clamp correct edge to intersection point
		if ( fDistance0 < REAL(0.0) ) 
		{
			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] - 
				dMUL((avArrayIn[i0][0]-avArrayIn[i1][0]),dDIV(fDistance0,(fDistance0-fDistance1)));
			vIntersectionPoint[1]= avArrayIn[i0][1] - 
				dMUL((avArrayIn[i0][1]-avArrayIn[i1][1]),dDIV(fDistance0,(fDistance0-fDistance1)));
			vIntersectionPoint[2]= avArrayIn[i0][2] - 
				dMUL((avArrayIn[i0][2]-avArrayIn[i1][2]),dDIV(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 (dVector3Length2(avArrayIn[i0]) <= dMUL(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] - 
				dMUL((avArrayIn[i0][0]-avArrayIn[i1][0]),dDIV(fDistance0,(fDistance0-fDistance1)));
			vIntersectionPoint[1]= avArrayIn[i0][1] - 
				dMUL((avArrayIn[i0][1]-avArrayIn[i1][1]),dDIV(fDistance0,(fDistance0-fDistance1)));
			vIntersectionPoint[2]= avArrayIn[i0][2] - 
				dMUL((avArrayIn[i0][2]-avArrayIn[i1][2]),dDIV(fDistance0,(fDistance0-fDistance1)));

			// emit intersection point
			if (dVector3Length2(avArrayIn[i0]) <= dMUL(fRadius,fRadius))
			{
				avArrayOut[ctOut][0] = vIntersectionPoint[0];
				avArrayOut[ctOut][1] = vIntersectionPoint[1];
				avArrayOut[ctOut][2] = vIntersectionPoint[2];
				ctOut++;
			}
		}
	}	
}