/*
** If the input is a well-formed JSON array of coordinates, where each
** coordinate is itself a two-value array, then convert the JSON into
** a GeoPoly object and return a pointer to that object.
**
** If any error occurs, return NULL.
*/
static GeoPoly *geopolyParseJson(const unsigned char *z){
  GeoParse s;

  memset(&s, 0, sizeof(s));
  s.z = z;
  if( geopolySkipSpace(&s)=='[' ){
    s.z++;
    while( geopolySkipSpace(&s)=='[' ){
      int ii = 0;
      char c;
      s.z++;
      if( s.nVertex<=s.nAlloc ){
        GeoCoord *aNew;
        s.nAlloc = s.nAlloc*2 + 16;
        aNew = sqlite3_realloc64(s.a, s.nAlloc*sizeof(GeoCoord)*2 );
        if( aNew==0 ){

          s.nErr++;
          break;
        }
        s.a = aNew;
      }
      while( geopolyParseNumber(&s, ii<=1 ? &s.a[s.nVertex*2+ii] : 0) ){
        ii++;
        if( ii==2 ) s.nVertex++;
        c = geopolySkipSpace(&s);
        s.z++;
        if( c==',' ) continue;
        if( c==']' ) break;
        s.nErr++;

        goto parse_json_err;
      }
      if( geopolySkipSpace(&s)==',' ){
        s.z++;
        continue;
      }
      break;
................................................................................
      pOut->nVertex = s.nVertex;
      memcpy(pOut->a, s.a, s.nVertex*2*sizeof(GeoCoord));
      pOut->hdr[0] = *(unsigned char*)&x;
      pOut->hdr[1] = (s.nVertex>>16)&0xff;
      pOut->hdr[2] = (s.nVertex>>8)&0xff;
      pOut->hdr[3] = s.nVertex&0xff;
      sqlite3_free(s.a);

      return pOut;
    }else{
      s.nErr++;

    }
  }
parse_json_err:

  sqlite3_free(s.a);
  return 0;
}

/*
** Given a function parameter, try to interpret it as a polygon, either
** in the binary format or JSON text.  Compute a GeoPoly object and
** return a pointer to that object.  Or if the input is not a well-formed
** polygon, put an error message in sqlite3_context and return NULL.
*/
static GeoPoly *geopolyFuncParam(sqlite3_context *pCtx, sqlite3_value *pVal){




  GeoPoly *p = 0;
  int nByte;
  if( sqlite3_value_type(pVal)==SQLITE_BLOB
   && (nByte = sqlite3_value_bytes(pVal))>=(4+6*sizeof(GeoCoord))
  ){
    const unsigned char *a = sqlite3_value_blob(pVal);
    int nVertex;
    nVertex = (a[1]<<16) + (a[2]<<8) + a[3];
    if( (a[0]==0 || a[0]==1)
     && (nVertex*2*sizeof(GeoCoord) + 4)==nByte
    ){
      p = sqlite3_malloc64( sizeof(*p) + (nVertex-1)*2*sizeof(GeoCoord) );
      if( p ){



        int x = 1;
        p->nVertex = nVertex;
        memcpy(p->hdr, a, nByte);
        if( a[0] != *(unsigned char*)&x ){
          int ii;
          for(ii=0; ii<nVertex*2; ii++){
            geopolySwab32((unsigned char*)&p->a[ii]);
          }
          p->hdr[0] ^= 1;
        }
      }
    }


  }else if( sqlite3_value_type(pVal)==SQLITE_TEXT ){
    p = geopolyParseJson(sqlite3_value_text(pVal));
  }
  if( p==0 ){


    sqlite3_result_error(pCtx, "not a valid polygon", -1);

  }
  return p;
}

/*
** Implementation of the geopoly_blob(X) function.
**
** If the input is a well-formed Geopoly BLOB or JSON string
** then return the BLOB representation of the polygon.  Otherwise
................................................................................
** return NULL.
*/
static void geopolyBlobFunc(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
){
  GeoPoly *p = geopolyFuncParam(context, argv[0]);
  if( p ){
    sqlite3_result_blob(context, p->hdr, 
       4+8*p->nVertex, SQLITE_TRANSIENT);
    sqlite3_free(p);
  }
}

................................................................................
** of coordinates.  Or, if X is not a valid polygon, return NULL.
*/
static void geopolyJsonFunc(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
){
  GeoPoly *p = geopolyFuncParam(context, argv[0]);
  if( p ){
    sqlite3 *db = sqlite3_context_db_handle(context);
    sqlite3_str *x = sqlite3_str_new(db);
    int i;
    sqlite3_str_append(x, "[", 1);
    for(i=0; i<p->nVertex; i++){
      sqlite3_str_appendf(x, "[%!g,%!g],", p->a[i*2], p->a[i*2+1]);
................................................................................
** Additional arguments are added as attributes to the <polyline>.
*/
static void geopolySvgFunc(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
){
  GeoPoly *p = geopolyFuncParam(context, argv[0]);
  if( p ){
    sqlite3 *db = sqlite3_context_db_handle(context);
    sqlite3_str *x = sqlite3_str_new(db);
    int i;
    char cSep = '\'';
    sqlite3_str_appendf(x, "<polyline points=");
    for(i=0; i<p->nVertex; i++){
................................................................................
** enclosed area.  Otherwise return NULL.
*/
static void geopolyAreaFunc(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
){
  GeoPoly *p = geopolyFuncParam(context, argv[0]);
  if( p ){
    double rArea = 0.0;
    int ii;
    for(ii=0; ii<p->nVertex-1; ii++){
      rArea += (p->a[ii*2] - p->a[ii*2+2])           /* (x0 - x1) */
                * (p->a[ii*2+1] + p->a[ii*2+3])      /* (y0 + y1) */
                * 0.5;
................................................................................
** Compute a bound-box on a polygon.  Return a new GeoPoly object
** that describes the bounding box.  Or, if aCoord is not a NULL pointer
** fill it in with the bounding box instead.
*/
static GeoPoly *geopolyBBox(
  sqlite3_context *context,   /* For recording the error */
  sqlite3_value *pPoly,       /* The polygon */
  double *aCoord              /* Results here */

){
  GeoPoly *p = geopolyFuncParam(context, pPoly);
  GeoPoly *pOut;
  if( p ){
    int ii;
    float mnX, mxX, mnY, mxY;
    mnX = mxX = p->a[0];
    mnY = mxY = p->a[1];
    for(ii=1; ii<p->nVertex; ii++){
      double r = p->a[ii*2];
      if( r<mnX ) mnX = r;
      else if( r>mxX ) mxX = r;
      r = p->a[ii*2+1];
      if( r<mnY ) mnY = r;
      else if( r>mxY ) mxY = r;
    }

    if( aCoord==0 ){
      pOut = sqlite3_realloc(p, sizeof(GeoPoly)+sizeof(GeoCoord)*6);
      if( pOut==0 ){
        sqlite3_free(p);
        sqlite3_result_error_nomem(context);

        return 0;
      }
      pOut->nVertex = 4;
      pOut->hdr[1] = 0;
      pOut->hdr[2] = 0;
      pOut->hdr[3] = 4;
      pOut->a[0] = mnX;
................................................................................
      pOut->a[1] = mnY;
      pOut->a[2] = mxX;
      pOut->a[3] = mnY;
      pOut->a[4] = mxX;
      pOut->a[5] = mxY;
      pOut->a[6] = mnX;
      pOut->a[7] = mxY;
      return pOut;
    }else{
      sqlite3_free(p);
      aCoord[0] = mnX;
      aCoord[1] = mxX;
      aCoord[2] = mnY;
      aCoord[3] = mxY;
      return (GeoPoly*)aCoord;
    }
  }
  return 0;
}

/*
** Implementation of the geopoly_bbox(X) SQL function.
*/
static void geopolyBBoxFunc(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
){
  GeoPoly *p = geopolyBBox(context, argv[0], 0);
  if( p ){
    sqlite3_result_blob(context, p->hdr, 
       4+8*p->nVertex, SQLITE_TRANSIENT);
    sqlite3_free(p);
  }
}

................................................................................
** Return 0 if point X,Y is outside the polygon
*/
static void geopolyWithinFunc(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
){
  GeoPoly *p = geopolyFuncParam(context, argv[0]);
  double x0 = sqlite3_value_double(argv[1]);
  double y0 = sqlite3_value_double(argv[2]);
  if( p ){
    int v = 0;
    int cnt = 0;
    int ii;
    for(ii=0; ii<p->nVertex-1; ii++){
................................................................................
**   NULL  Either P1 or P2 or both are not valid polygons
*/
static void geopolyOverlapFunc(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
){
  GeoPoly *p1 = geopolyFuncParam(context, argv[0]);
  GeoPoly *p2 = geopolyFuncParam(context, argv[1]);
  if( p1 && p2 ){
    int x = geopolyOverlap(p1, p2);
    if( x<0 ){
      sqlite3_result_error_nomem(context);
    }else{
      sqlite3_result_int(context, x);
    }
................................................................................
  /* Create/Connect to the underlying relational database schema. If
  ** that is successful, call sqlite3_declare_vtab() to configure
  ** the r-tree table schema.
  */
  pSql = sqlite3_str_new(db);
  sqlite3_str_appendf(pSql, "CREATE TABLE x");
  cSep = '(';

  for(ii=3; ii<argc; ii++){
    pRtree->nAux++;
    sqlite3_str_appendf(pSql, "%c%s", cSep, argv[ii]+1);
    cSep = ',';
  }
  sqlite3_str_appendf(pSql, "%c _poly HIDDEN, _bbox HIDDEN);", cSep);
  zSql = sqlite3_str_finish(pSql);
  if( !zSql ){
    rc = SQLITE_NOMEM;
  }else if( SQLITE_OK!=(rc = sqlite3_declare_vtab(db, zSql)) ){
    *pzErr = sqlite3_mprintf("%s", sqlite3_errmsg(db));
  }
  sqlite3_free(zSql);
................................................................................
  sqlite3_vtab *pVtab, 
  int nData, 
  sqlite3_value **aData, 
  sqlite_int64 *pRowid
){
  Rtree *pRtree = (Rtree *)pVtab;
  int rc = SQLITE_OK;
//  RtreeCell cell;                 /* New cell to insert if nData>1 */
//  int bHaveRowid = 0;             /* Set to 1 after new rowid is determined */
//  int iShapeCol;                  /* Index of the _shape column */






  if( pRtree->nNodeRef ){
    /* Unable to write to the btree while another cursor is reading from it,
    ** since the write might do a rebalance which would disrupt the read
    ** cursor. */
    return SQLITE_LOCKED_VTAB;
  }
  rtreeReference(pRtree);
  assert(nData>=1);

//  cell.iRowid = 0;  /* Used only to suppress a compiler warning */
//  iShapeCol = pRtree->nAux;

  rc = SQLITE_ERROR;




#if 0


  /* Constraint handling. A write operation on an r-tree table may return
  ** SQLITE_CONSTRAINT for two reasons:
  **
  **   1. A duplicate rowid value, or
  **   2. The supplied data violates the "x2>=x1" constraint.
  **
  ** In the first case, if the conflict-handling mode is REPLACE, then
  ** the conflicting row can be removed before proceeding. In the second
  ** case, SQLITE_CONSTRAINT must be returned regardless of the
  ** conflict-handling mode specified by the user.
  */
  if( nData>1 
   && (!sqlite3_value_nochange(aData[iShapeCol+2])

  ){






#ifndef SQLITE_RTREE_INT_ONLY
    if( pRtree->eCoordType==RTREE_COORD_REAL32 ){
      for(ii=0; ii<nn; ii+=2){
        cell.aCoord[ii].f = rtreeValueDown(aData[ii+3]);
        cell.aCoord[ii+1].f = rtreeValueUp(aData[ii+4]);
        if( cell.aCoord[ii].f>cell.aCoord[ii+1].f ){
          rc = rtreeConstraintError(pRtree, ii+1);
          goto constraint;

        }

      }
    }else
#endif
    {
      for(ii=0; ii<nn; ii+=2){
        cell.aCoord[ii].i = sqlite3_value_int(aData[ii+3]);
        cell.aCoord[ii+1].i = sqlite3_value_int(aData[ii+4]);
        if( cell.aCoord[ii].i>cell.aCoord[ii+1].i ){
          rc = rtreeConstraintError(pRtree, ii+1);
          goto constraint;
        }
      }
    }

    /* If a rowid value was supplied, check if it is already present in 
    ** the table. If so, the constraint has failed. */
    if( sqlite3_value_type(aData[2])!=SQLITE_NULL ){
      cell.iRowid = sqlite3_value_int64(aData[2]);
      if( sqlite3_value_type(aData[0])==SQLITE_NULL
       || sqlite3_value_int64(aData[0])!=cell.iRowid
      ){

        int steprc;
        sqlite3_bind_int64(pRtree->pReadRowid, 1, cell.iRowid);
        steprc = sqlite3_step(pRtree->pReadRowid);
        rc = sqlite3_reset(pRtree->pReadRowid);
        if( SQLITE_ROW==steprc ){
          if( sqlite3_vtab_on_conflict(pRtree->db)==SQLITE_REPLACE ){
            rc = rtreeDeleteRowid(pRtree, cell.iRowid);
          }else{
            rc = rtreeConstraintError(pRtree, 0);
            goto constraint;
          }
        }
      }
      bHaveRowid = 1;
    }
  }

  /* If aData[0] is not an SQL NULL value, it is the rowid of a
  ** record to delete from the r-tree table. The following block does
  ** just that.
  */
  if( sqlite3_value_type(aData[0])!=SQLITE_NULL ){
    rc = rtreeDeleteRowid(pRtree, sqlite3_value_int64(aData[0]));
  }

  /* If the aData[] array contains more than one element, elements
  ** (aData[2]..aData[argc-1]) contain a new record to insert into
  ** the r-tree structure.
  */
  if( rc==SQLITE_OK && nData>1 ){
    /* Insert the new record into the r-tree */
    RtreeNode *pLeaf = 0;

    /* Figure out the rowid of the new row. */
    if( bHaveRowid==0 ){
      rc = newRowid(pRtree, &cell.iRowid);
    }
    *pRowid = cell.iRowid;

    if( rc==SQLITE_OK ){
      rc = ChooseLeaf(pRtree, &cell, 0, &pLeaf);
    }
    if( rc==SQLITE_OK ){
      int rc2;
      pRtree->iReinsertHeight = -1;
      rc = rtreeInsertCell(pRtree, pLeaf, &cell, 0);
      rc2 = nodeRelease(pRtree, pLeaf);
      if( rc==SQLITE_OK ){
        rc = rc2;
      }
    }



    if( pRtree->nAux ){
      sqlite3_stmt *pUp = pRtree->pWriteAux;
      int jj;

      sqlite3_bind_int64(pUp, 1, *pRowid);
      for(jj=0; jj<pRtree->nAux; jj++){

        sqlite3_bind_value(pUp, jj+2, aData[pRtree->nDim2+3+jj]);
      }

      sqlite3_step(pUp);
      rc = sqlite3_reset(pUp);
    }
  }
constraint:
#endif /* 0 */

  rtreeRelease(pRtree);
  return rc;
}

static sqlite3_module geopolyModule = {
  2,                          /* iVersion */

/*
** If the input is a well-formed JSON array of coordinates, where each
** coordinate is itself a two-value array, then convert the JSON into
** a GeoPoly object and return a pointer to that object.
**
** If any error occurs, return NULL.
*/
static GeoPoly *geopolyParseJson(const unsigned char *z, int *pRc){
  GeoParse s;
  int rc = SQLITE_OK;
  memset(&s, 0, sizeof(s));
  s.z = z;
  if( geopolySkipSpace(&s)=='[' ){
    s.z++;
    while( geopolySkipSpace(&s)=='[' ){
      int ii = 0;
      char c;
      s.z++;
      if( s.nVertex<=s.nAlloc ){
        GeoCoord *aNew;
        s.nAlloc = s.nAlloc*2 + 16;
        aNew = sqlite3_realloc64(s.a, s.nAlloc*sizeof(GeoCoord)*2 );
        if( aNew==0 ){
          rc = SQLITE_NOMEM;
          s.nErr++;
          break;
        }
        s.a = aNew;
      }
      while( geopolyParseNumber(&s, ii<=1 ? &s.a[s.nVertex*2+ii] : 0) ){
        ii++;
        if( ii==2 ) s.nVertex++;
        c = geopolySkipSpace(&s);
        s.z++;
        if( c==',' ) continue;
        if( c==']' ) break;
        s.nErr++;
        rc = SQLITE_ERROR;
        goto parse_json_err;
      }
      if( geopolySkipSpace(&s)==',' ){
        s.z++;
        continue;
      }
      break;
................................................................................
      pOut->nVertex = s.nVertex;
      memcpy(pOut->a, s.a, s.nVertex*2*sizeof(GeoCoord));
      pOut->hdr[0] = *(unsigned char*)&x;
      pOut->hdr[1] = (s.nVertex>>16)&0xff;
      pOut->hdr[2] = (s.nVertex>>8)&0xff;
      pOut->hdr[3] = s.nVertex&0xff;
      sqlite3_free(s.a);
      if( pRc ) *pRc = SQLITE_OK;
      return pOut;
    }else{
      s.nErr++;
      rc = SQLITE_ERROR;
    }
  }
parse_json_err:
  if( pRc ) *pRc = rc;
  sqlite3_free(s.a);
  return 0;
}

/*
** Given a function parameter, try to interpret it as a polygon, either
** in the binary format or JSON text.  Compute a GeoPoly object and
** return a pointer to that object.  Or if the input is not a well-formed
** polygon, put an error message in sqlite3_context and return NULL.
*/
static GeoPoly *geopolyFuncParam(
  sqlite3_context *pCtx,      /* Context for error messages */
  sqlite3_value *pVal,        /* The value to decode */
  int *pRc                    /* Write error here */
){
  GeoPoly *p = 0;
  int nByte;
  if( sqlite3_value_type(pVal)==SQLITE_BLOB
   && (nByte = sqlite3_value_bytes(pVal))>=(4+6*sizeof(GeoCoord))
  ){
    const unsigned char *a = sqlite3_value_blob(pVal);
    int nVertex;
    nVertex = (a[1]<<16) + (a[2]<<8) + a[3];
    if( (a[0]==0 || a[0]==1)
     && (nVertex*2*sizeof(GeoCoord) + 4)==nByte
    ){
      p = sqlite3_malloc64( sizeof(*p) + (nVertex-1)*2*sizeof(GeoCoord) );
      if( p==0 ){
        if( pRc ) *pRc = SQLITE_NOMEM;
        if( pCtx ) sqlite3_result_error_nomem(pCtx);
      }else{
        int x = 1;
        p->nVertex = nVertex;
        memcpy(p->hdr, a, nByte);
        if( a[0] != *(unsigned char*)&x ){
          int ii;
          for(ii=0; ii<nVertex*2; ii++){
            geopolySwab32((unsigned char*)&p->a[ii]);
          }
          p->hdr[0] ^= 1;
        }
      }
    }
    if( pRc ) *pRc = SQLITE_OK;
    return p;
  }else if( sqlite3_value_type(pVal)==SQLITE_TEXT ){
    return geopolyParseJson(sqlite3_value_text(pVal), pRc);


  }else{
    *pRc = SQLITE_ERROR;
    if( pCtx!=0 ) sqlite3_result_error(pCtx, "not a valid polygon", -1);
    return 0;
  }

}

/*
** Implementation of the geopoly_blob(X) function.
**
** If the input is a well-formed Geopoly BLOB or JSON string
** then return the BLOB representation of the polygon.  Otherwise
................................................................................
** return NULL.
*/
static void geopolyBlobFunc(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
){
  GeoPoly *p = geopolyFuncParam(context, argv[0], 0);
  if( p ){
    sqlite3_result_blob(context, p->hdr, 
       4+8*p->nVertex, SQLITE_TRANSIENT);
    sqlite3_free(p);
  }
}

................................................................................
** of coordinates.  Or, if X is not a valid polygon, return NULL.
*/
static void geopolyJsonFunc(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
){
  GeoPoly *p = geopolyFuncParam(context, argv[0], 0);
  if( p ){
    sqlite3 *db = sqlite3_context_db_handle(context);
    sqlite3_str *x = sqlite3_str_new(db);
    int i;
    sqlite3_str_append(x, "[", 1);
    for(i=0; i<p->nVertex; i++){
      sqlite3_str_appendf(x, "[%!g,%!g],", p->a[i*2], p->a[i*2+1]);
................................................................................
** Additional arguments are added as attributes to the <polyline>.
*/
static void geopolySvgFunc(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
){
  GeoPoly *p = geopolyFuncParam(context, argv[0], 0);
  if( p ){
    sqlite3 *db = sqlite3_context_db_handle(context);
    sqlite3_str *x = sqlite3_str_new(db);
    int i;
    char cSep = '\'';
    sqlite3_str_appendf(x, "<polyline points=");
    for(i=0; i<p->nVertex; i++){
................................................................................
** enclosed area.  Otherwise return NULL.
*/
static void geopolyAreaFunc(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
){
  GeoPoly *p = geopolyFuncParam(context, argv[0], 0);
  if( p ){
    double rArea = 0.0;
    int ii;
    for(ii=0; ii<p->nVertex-1; ii++){
      rArea += (p->a[ii*2] - p->a[ii*2+2])           /* (x0 - x1) */
                * (p->a[ii*2+1] + p->a[ii*2+3])      /* (y0 + y1) */
                * 0.5;
................................................................................
** Compute a bound-box on a polygon.  Return a new GeoPoly object
** that describes the bounding box.  Or, if aCoord is not a NULL pointer
** fill it in with the bounding box instead.
*/
static GeoPoly *geopolyBBox(
  sqlite3_context *context,   /* For recording the error */
  sqlite3_value *pPoly,       /* The polygon */
  RtreeCoord *aCoord,         /* Results here */
  int *pRc                    /* Error code here */
){
  GeoPoly *p = geopolyFuncParam(context, pPoly, pRc);
  GeoPoly *pOut = 0;
  if( p ){
    int ii;
    float mnX, mxX, mnY, mxY;
    mnX = mxX = p->a[0];
    mnY = mxY = p->a[1];
    for(ii=1; ii<p->nVertex; ii++){
      double r = p->a[ii*2];
      if( r<mnX ) mnX = r;
      else if( r>mxX ) mxX = r;
      r = p->a[ii*2+1];
      if( r<mnY ) mnY = r;
      else if( r>mxY ) mxY = r;
    }
    if( pRc ) *pRc = SQLITE_OK;
    if( aCoord==0 ){
      pOut = sqlite3_realloc(p, sizeof(GeoPoly)+sizeof(GeoCoord)*6);
      if( pOut==0 ){
        sqlite3_free(p);
        if( context ) sqlite3_result_error_nomem(context);
        if( pRc ) *pRc = SQLITE_NOMEM;
        return 0;
      }
      pOut->nVertex = 4;
      pOut->hdr[1] = 0;
      pOut->hdr[2] = 0;
      pOut->hdr[3] = 4;
      pOut->a[0] = mnX;
................................................................................
      pOut->a[1] = mnY;
      pOut->a[2] = mxX;
      pOut->a[3] = mnY;
      pOut->a[4] = mxX;
      pOut->a[5] = mxY;
      pOut->a[6] = mnX;
      pOut->a[7] = mxY;

    }else{
      sqlite3_free(p);
      aCoord[0].f = mnX;
      aCoord[1].f = mxX;
      aCoord[2].f = mnY;
      aCoord[3].f = mxY;

    }
  }
  return pOut;
}

/*
** Implementation of the geopoly_bbox(X) SQL function.
*/
static void geopolyBBoxFunc(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
){
  GeoPoly *p = geopolyBBox(context, argv[0], 0, 0);
  if( p ){
    sqlite3_result_blob(context, p->hdr, 
       4+8*p->nVertex, SQLITE_TRANSIENT);
    sqlite3_free(p);
  }
}

................................................................................
** Return 0 if point X,Y is outside the polygon
*/
static void geopolyWithinFunc(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
){
  GeoPoly *p = geopolyFuncParam(context, argv[0], 0);
  double x0 = sqlite3_value_double(argv[1]);
  double y0 = sqlite3_value_double(argv[2]);
  if( p ){
    int v = 0;
    int cnt = 0;
    int ii;
    for(ii=0; ii<p->nVertex-1; ii++){
................................................................................
**   NULL  Either P1 or P2 or both are not valid polygons
*/
static void geopolyOverlapFunc(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
){
  GeoPoly *p1 = geopolyFuncParam(context, argv[0], 0);
  GeoPoly *p2 = geopolyFuncParam(context, argv[1], 0);
  if( p1 && p2 ){
    int x = geopolyOverlap(p1, p2);
    if( x<0 ){
      sqlite3_result_error_nomem(context);
    }else{
      sqlite3_result_int(context, x);
    }
................................................................................
  /* Create/Connect to the underlying relational database schema. If
  ** that is successful, call sqlite3_declare_vtab() to configure
  ** the r-tree table schema.
  */
  pSql = sqlite3_str_new(db);
  sqlite3_str_appendf(pSql, "CREATE TABLE x");
  cSep = '(';
  pRtree->nAux = 1;   /* Add one for _shape */
  for(ii=3; ii<argc; ii++){
    pRtree->nAux++;
    sqlite3_str_appendf(pSql, "%c%s", cSep, argv[ii]+1);
    cSep = ',';
  }
  sqlite3_str_appendf(pSql, "%c _shape, _bbox HIDDEN);", cSep);
  zSql = sqlite3_str_finish(pSql);
  if( !zSql ){
    rc = SQLITE_NOMEM;
  }else if( SQLITE_OK!=(rc = sqlite3_declare_vtab(db, zSql)) ){
    *pzErr = sqlite3_mprintf("%s", sqlite3_errmsg(db));
  }
  sqlite3_free(zSql);
................................................................................
  sqlite3_vtab *pVtab, 
  int nData, 
  sqlite3_value **aData, 
  sqlite_int64 *pRowid
){
  Rtree *pRtree = (Rtree *)pVtab;
  int rc = SQLITE_OK;
  RtreeCell cell;                 /* New cell to insert if nData>1 */

  int iShapeCol;                  /* Index of the _shape column */
  i64 oldRowid;                   /* The old rowid */
  int oldRowidValid;              /* True if oldRowid is valid */
  i64 newRowid;                   /* The new rowid */
  int newRowidValid;              /* True if newRowid is valid */
  int coordChange = 0;            /* Change in coordinates */

  if( pRtree->nNodeRef ){
    /* Unable to write to the btree while another cursor is reading from it,
    ** since the write might do a rebalance which would disrupt the read
    ** cursor. */
    return SQLITE_LOCKED_VTAB;
  }
  rtreeReference(pRtree);
  assert(nData>=1);


  iShapeCol = pRtree->nAux;

  rc = SQLITE_ERROR;

  oldRowidValid = sqlite3_value_type(aData[0])!=SQLITE_NULL;;
  oldRowid = oldRowidValid ? sqlite3_value_int64(aData[0]) : 0;
  newRowidValid = nData>1 && sqlite3_value_type(aData[1])!=SQLITE_NULL;
  newRowid = newRowidValid ? sqlite3_value_int64(aData[1]) : 0;
  cell.iRowid = newRowid;


  if( nData>1                                           /* not a DELETE */
   && (!oldRowidValid                                   /* INSERT */









        || !sqlite3_value_nochange(aData[iShapeCol+2])  /* UPDATE _shape */
        || oldRowid!=newRowid)                          /* Rowid change */
  ){
    geopolyBBox(0, aData[iShapeCol+2], cell.aCoord, &rc);
    if( rc ){
      if( rc==SQLITE_ERROR ){
        pVtab->zErrMsg =
          sqlite3_mprintf("_shape does not contain a valid polygon");
      }








      return rc;
    }
    coordChange = 1;














    /* If a rowid value was supplied, check if it is already present in 
    ** the table. If so, the constraint has failed. */





    if( oldRowidValid && oldRowid!=newRowid ){
      int steprc;
      sqlite3_bind_int64(pRtree->pReadRowid, 1, cell.iRowid);
      steprc = sqlite3_step(pRtree->pReadRowid);
      rc = sqlite3_reset(pRtree->pReadRowid);
      if( SQLITE_ROW==steprc ){
        if( sqlite3_vtab_on_conflict(pRtree->db)==SQLITE_REPLACE ){
          rc = rtreeDeleteRowid(pRtree, cell.iRowid);
        }else{
          rc = rtreeConstraintError(pRtree, 0);

        }
      }


    }
  }

  /* If aData[0] is not an SQL NULL value, it is the rowid of a
  ** record to delete from the r-tree table. The following block does
  ** just that.
  */
  if( rc==SQLITE_OK && (nData==1 || coordChange) ){
    rc = rtreeDeleteRowid(pRtree, oldRowid);
  }

  /* If the aData[] array contains more than one element, elements
  ** (aData[2]..aData[argc-1]) contain a new record to insert into
  ** the r-tree structure.
  */
  if( rc==SQLITE_OK && nData>1 && coordChange ){
    /* Insert the new record into the r-tree */
    RtreeNode *pLeaf = 0;





    *pRowid = cell.iRowid;

    if( rc==SQLITE_OK ){
      rc = ChooseLeaf(pRtree, &cell, 0, &pLeaf);
    }
    if( rc==SQLITE_OK ){
      int rc2;
      pRtree->iReinsertHeight = -1;
      rc = rtreeInsertCell(pRtree, pLeaf, &cell, 0);
      rc2 = nodeRelease(pRtree, pLeaf);
      if( rc==SQLITE_OK ){
        rc = rc2;
      }
    }
  }

  /* Change the data */
  if( rc==SQLITE_OK && pRtree->nAux>0 ){
    sqlite3_stmt *pUp = pRtree->pWriteAux;
    int jj;
    int nChange = 0;
    sqlite3_bind_int64(pUp, 1, newRowid);
    for(jj=0; jj<pRtree->nAux; jj++){
      if( !sqlite3_value_nochange(aData[jj+2]) ) nChange++;
      sqlite3_bind_value(pUp, jj+2, aData[jj+2]);
    }
    if( nChange ){
      sqlite3_step(pUp);
      rc = sqlite3_reset(pUp);
    }
  }



  rtreeRelease(pRtree);
  return rc;
}

static sqlite3_module geopolyModule = {
  2,                          /* iVersion */