text: /*
  Bullet Continuous Collision Detection and Physics Library
  Copyright (c) 2003-2006 Erwin Coumans http://continuousphysics.com/Bullet/
  
  This software is provided 'as-is', without any express or implied warranty.
  In no event will the authors be held liable for any damages arising from the use of this software.
  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it freely,
  subject to the following restrictions:
  
  1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.
  */
  ///btSparseSdf implementation by Nathanael Presson
  
  #ifndef BT_SPARSE_SDF_H
  #define BT_SPARSE_SDF_H
  
  #include "BulletCollision/CollisionDispatch/btCollisionObject.h"
  #include "BulletCollision/NarrowPhaseCollision/btGjkEpa2.h"
  
  // Modified Paul Hsieh hash
  template <const int DWORDLEN>
  unsigned int HsiehHash(const void* pdata)
  {
  const unsigned short* data=(const unsigned short*)pdata;
  unsigned hash=DWORDLEN<<2,tmp;
  for(int i=0;i<DWORDLEN;++i)
  {
  hash += data[0];
  tmp = (data[1]<<11)^hash;
  hash = (hash<<16)^tmp;
  data += 2;
  hash += hash>>11;
  }
  hash^=hash<<3;hash+=hash>>5;
  hash^=hash<<4;hash+=hash>>17;
  hash^=hash<<25;hash+=hash>>6;
  return(hash);
  }
  
  template <const int CELLSIZE>
  struct btSparseSdf
  {
  //
  // Inner types
  //
  struct IntFrac
  {
  int b;
  int i;
  btScalar f;
  };
  struct Cell
  {
  btScalar d[CELLSIZE+1][CELLSIZE+1][CELLSIZE+1];
  int c[3];
  int puid;
  unsigned hash;
  btCollisionShape* pclient;
  Cell* next;
  };
  //
  // Fields
  //
  
  btAlignedObjectArray<Cell*> cells;
  btScalar voxelsz;
  int puid;
  int ncells;
  int nprobes;
  int nqueries;
  
  //
  // Methods
  //
  
  //
  void Initialize(int hashsize=2383)
  {
  cells.resize(hashsize,0);
  Reset();
  }
  //
  void Reset()
  {
  for(int i=0,ni=cells.size();i<ni;++i)
  {
  Cell* pc=cells[i];
  cells[i]=0;
  while(pc)
  {
  Cell* pn=pc->next;
  delete pc;
  pc=pn;
  }
  }
  voxelsz =0.25;
  puid =0;
  ncells =0;
  nprobes =1;
  nqueries =1;
  }
  //
  void GarbageCollect(int lifetime=256)
  {
  const int life=puid-lifetime;
  for(int i=0;i<cells.size();++i)
  {
  Cell*& root=cells[i];
  Cell* pp=0;
  Cell* pc=root;
  while(pc)
  {
  Cell* pn=pc->next;
  if(pc->puid<life)
  {
  if(pp) pp->next=pn; else root=pn;
  delete pc;pc=pp;--ncells;
  }
  pp=pc;pc=pn;
  }
  }
  //printf("GC[%d]: %d cells, PpQ: %f\r\n",puid,ncells,nprobes/(btScalar)nqueries);
  nqueries=1;
  nprobes=1;
  ++puid; ///@todo: Reset puid's when int range limit is reached */
  /* else setup a priority list... */
  }
  //
  int RemoveReferences(btCollisionShape* pcs)
  {
  int refcount=0;
  for(int i=0;i<cells.size();++i)
  {
  Cell*& root=cells[i];
  Cell* pp=0;
  Cell* pc=root;
  while(pc)
  {
  Cell* pn=pc->next;
  if(pc->pclient==pcs)
  {
  if(pp) pp->next=pn; else root=pn;
  delete pc;pc=pp;++refcount;
  }
  pp=pc;pc=pn;
  }
  }
  return(refcount);
  }
  //
  btScalar Evaluate( const btVector3& x,
  btCollisionShape* shape,
  btVector3& normal,
  btScalar margin)
  {
  /* Lookup cell */
  const btVector3 scx=x/voxelsz;
  const IntFrac ix=Decompose(scx.x());
  const IntFrac iy=Decompose(scx.y());
  const IntFrac iz=Decompose(scx.z());
  const unsigned h=Hash(ix.b,iy.b,iz.b,shape);
  Cell*& root=cells[static_cast<int>(h%cells.size())];
  Cell* c=root;
  ++nqueries;
  while(c)
  {
  ++nprobes;
  if( (c->hash==h) &&
  (c->c[0]==ix.b) &&
  (c->c[1]==iy.b) &&
  (c->c[2]==iz.b) &&
  (c->pclient==shape))
  { break; }
  else
  { c=c->next; }
  }
  if(!c)
  {
  ++nprobes;
  ++ncells;
  c=new Cell();
  c->next=root;root=c;
  c->pclient=shape;
  c->hash=h;
  c->c[0]=ix.b;c->c[1]=iy.b;c->c[2]=iz.b;
  BuildCell(*c);
  }
  c->puid=puid;
  /* Extract infos */
  const int o[]={ ix.i,iy.i,iz.i};
  const btScalar d[]={ c->d[o[0]+0][o[1]+0][o[2]+0],
  c->d[o[0]+1][o[1]+0][o[2]+0],
  c->d[o[0]+1][o[1]+1][o[2]+0],
  c->d[o[0]+0][o[1]+1][o[2]+0],
  c->d[o[0]+0][o[1]+0][o[2]+1],
  c->d[o[0]+1][o[1]+0][o[2]+1],
  c->d[o[0]+1][o[1]+1][o[2]+1],
  c->d[o[0]+0][o[1]+1][o[2]+1]};
  /* Normal */
  #if 1
  const btScalar gx[]={ d[1]-d[0],d[2]-d[3],
  d[5]-d[4],d[6]-d[7]};
  const btScalar gy[]={ d[3]-d[0],d[2]-d[1],
  d[7]-d[4],d[6]-d[5]};
  const btScalar gz[]={ d[4]-d[0],d[5]-d[1],
  d[7]-d[3],d[6]-d[2]};
  normal.setX(Lerp( Lerp(gx[0],gx[1],iy.f),
  Lerp(gx[2],gx[3],iy.f),iz.f));
  normal.setY(Lerp( Lerp(gy[0],gy[1],ix.f),
  Lerp(gy[2],gy[3],ix.f),iz.f));
  normal.setZ(Lerp( Lerp(gz[0],gz[1],ix.f),
  Lerp(gz[2],gz[3],ix.f),iy.f));
  normal = normal.normalized();
  #else
  normal = btVector3(d[1]-d[0],d[3]-d[0],d[4]-d[0]).normalized();
  #endif
  /* Distance */
  const btScalar d0=Lerp(Lerp(d[0],d[1],ix.f),
  Lerp(d[3],d[2],ix.f),iy.f);
  const btScalar d1=Lerp(Lerp(d[4],d[5],ix.f),
  Lerp(d[7],d[6],ix.f),iy.f);
  return(Lerp(d0,d1,iz.f)-margin);
  }
  //
  void BuildCell(Cell& c)
  {
  const btVector3 org=btVector3( (btScalar)c.c[0],
  (btScalar)c.c[1],
  (btScalar)c.c[2]) *
  CELLSIZE*voxelsz;
  for(int k=0;k<=CELLSIZE;++k)
  {
  const btScalar z=voxelsz*k+org.z();
  for(int j=0;j<=CELLSIZE;++j)
  {
  const btScalar y=voxelsz*j+org.y();
  for(int i=0;i<=CELLSIZE;++i)
  {
  const btScalar x=voxelsz*i+org.x();
  c.d[i][j][k]=DistanceToShape( btVector3(x,y,z),
  c.pclient);
  }
  }
  }
  }
  //
  static inline btScalar DistanceToShape(const btVector3& x,
  btCollisionShape* shape)
  {
  btTransform unit;
  unit.setIdentity();
  if(shape->isConvex())
  {
  btGjkEpaSolver2::sResults res;
  btConvexShape* csh=static_cast<btConvexShape*>(shape);
  return(btGjkEpaSolver2::SignedDistance(x,0,csh,unit,res));
  }
  return(0);
  }
  //
  static inline IntFrac Decompose(btScalar x)
  {
  /* That one need a lot of improvements... */
  /* Remove test, faster floor... */
  IntFrac r;
  x/=CELLSIZE;
  const int o=x<0?(int)(-x+1):0;
  x+=o;r.b=(int)x;
  const btScalar k=(x-r.b)*CELLSIZE;
  r.i=(int)k;r.f=k-r.i;r.b-=o;
  return(r);
  }
  //
  static inline btScalar Lerp(btScalar a,btScalar b,btScalar t)
  {
  return(a+(b-a)*t);
  }
  
  
  
  //
  static inline unsigned int Hash(int x,int y,int z,btCollisionShape* shape)
  {
  struct btS
  {
  int x,y,z;
  void* p;
  };
  
  btS myset;
  
  myset.x=x;myset.y=y;myset.z=z;myset.p=shape;
  const void* ptr = &myset;
  
  unsigned int result = HsiehHash<sizeof(btS)/4> (ptr);
  
  
  return result;
  }
  };
  
  
  #endif //BT_SPARSE_SDF_H
  