问如何在PostgreSQL库中开发PostGIS扩展

EN

#include "../postgis_config.h"
#include "liblwgeom.h"
#include "lwgeom_pg.h"

#include "postgres.h"           
#include "fmgr.h"
#include <utils/geo_decls.h>    
#include "utils/builtins.h"

Datum pg_xytile_to_box(PG_FUNCTION_ARGS)
{
    int x, y, zoom;
    struct tile_box box;
    BOX *pg_box = (BOX *) palloc(sizeof(BOX));

    x = PG_GETARG_INT64(0);
    y = PG_GETARG_INT64(1);
    zoom = PG_GETARG_INT32(2);

    if ( xytile_to_box(&box, x, y, zoom) != 0 )
    {
        pfree(pg_box);
        PG_RETURN_NULL();
    }

    pg_box->low.x = box.w;
    pg_box->low.y = box.s;
    pg_box->high.x = box.e;
    pg_box->high.y = box.n;

    PG_RETURN_BOX_P(pg_box);
}

PG_FUNCTION_INFO_V1(pg_xytile_to_box);

CREATE OR REPLACE FUNCTION _xytile_to_box(x int, y int, zoom int default 11) RETURNS box
    AS 'MODULE_PATHNAME', 'pg_xytile_to_box'
 LANGUAGE C IMMUTABLE STRICT;

CREATE OR REPLACE FUNCTION xtile_to_geom(xtile int, ytile int, zoom int default 11) returns geometry(polygon, 4326)
language plpgsql security definer as $FUNC$
BEGIN
return (
select st_setsrid((ST_MakeBox2D(b[0]::geometry(point), b[1]::geometry(point)))::geometry(polygon), 4326) as t
from _xytile_to_box(xtile, ytile, zoom) as b
);
END; $FUNC$;