SQLite

  }
  y = y1 + (y2-y1)*(x0-x1)/(x2-x1);
  if( y0==y ) return 2;
  if( y0<y ) return 1;
  return 0;
}




/*
** SQL function:    geopoly_contains_point(P,X,Y)
**
** Return +2 if point X,Y is within polygon P.
** Return +1 if point X,Y is on the polygon boundary.
** Return 0 if point X,Y is outside the polygon
*/
static void geopolyContainsPointFunc(
  sqlite3_context *context,
  int argc,
  sqlite3_value **argv
){
  GeoPoly *p1 = geopolyFuncParam(context, argv[0], 0);
  double x0 = sqlite3_value_double(argv[1]);
  double y0 = sqlite3_value_double(argv[2]);
  int v = 0;
  int cnt = 0;
  int ii;
  if( p1==0 ) return;
  for(ii=0; ii<p1->nVertex-1; ii++){
    v = pointBeneathLine(x0,y0,p1->a[ii*2],p1->a[ii*2+1],
                               p1->a[ii*2+2],p1->a[ii*2+3]);
    if( v==2 ) break;
    cnt += v;
  }
  if( v!=2 ){
    v = pointBeneathLine(x0,y0,p1->a[ii*2],p1->a[ii*2+1],
                               p1->a[0],p1->a[1]);
  }
  if( v==2 ){
    sqlite3_result_int(context, 1);
  }else if( ((v+cnt)&1)==0 ){
    sqlite3_result_int(context, 0);
  }else{
    sqlite3_result_int(context, 2);
  }
  sqlite3_free(p1);
}

/* Forward declaration */
static int geopolyOverlap(GeoPoly *p1, GeoPoly *p2);

/*
** SQL function:    geopoly_within(P1,P2)
**
** Return +2 if P1 and P2 are the same polygon
** Return +1 if P2 is contained within P1
** Return 0 if any part of P2 is on the outside of P1
**
*/
static void geopolyWithinFunc(
  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==2 ? 1 : x==4 ? 2 : 0);
    }

  }

  sqlite3_free(p1);
  sqlite3_free(p2);
}

/* Objects used by the overlap algorihm. */
typedef struct GeoEvent GeoEvent;
typedef struct GeoSegment GeoSegment;
typedef struct GeoOverlap GeoOverlap;
struct GeoEvent {

  void **ppArg
){
  if( sqlite3_stricmp(zName, "geopoly_overlap")==0 ){
    *pxFunc = geopolyOverlapFunc;
    *ppArg = 0;
    return SQLITE_INDEX_CONSTRAINT_FUNCTION;
  }
  if( sqlite3_stricmp(zName, "geopoly_within")==0 ){
    *pxFunc = geopolyWithinFunc;
    *ppArg = 0;
    return SQLITE_INDEX_CONSTRAINT_FUNCTION+1;
  }
  return 0;
}

static int sqlite3_geopoly_init(sqlite3 *db){
  int rc = SQLITE_OK;
  static const struct {
    void (*xFunc)(sqlite3_context*,int,sqlite3_value**);
    int nArg;
    const char *zName;
  } aFunc[] = {
     { geopolyAreaFunc,          1,    "geopoly_area"             },
     { geopolyBlobFunc,          1,    "geopoly_blob"             },
     { geopolyJsonFunc,          1,    "geopoly_json"             },
     { geopolySvgFunc,          -1,    "geopoly_svg"              },
     { geopolyWithinFunc,        2,    "geopoly_within"           },
     { geopolyContainsPointFunc, 3,    "geopoly_contains_point"   },
     { geopolyOverlapFunc,       2,    "geopoly_overlap"          },
     { geopolyDebugFunc,         1,    "geopoly_debug"            },
     { geopolyBBoxFunc,          1,    "geopoly_bbox"             },
     { geopolyXformFunc,         7,    "geopoly_xform"            },
  };
  int i;
  for(i=0; i<sizeof(aFunc)/sizeof(aFunc[0]) && rc==SQLITE_OK; i++){
    rc = sqlite3_create_function(db, aFunc[i].zName, aFunc[i].nArg,
                                 SQLITE_UTF8, 0,
                                 aFunc[i].xFunc, 0, 0);
  }
  if( rc==SQLITE_OK ){
    rc = sqlite3_create_module_v2(db, "geopoly", &geopolyModule, 0, 0);
  }
  return rc;
}