/*
* $Id: gsdiff.c,v 2.1 2006/02/09 03:08:57 glynn Exp $
*/

/*  gsdiff.c
    Bill Brown, USACERL  
    November 1994
routines to set up automatic on-the-fly recalculation
of surface elevations, doing a "scaled difference" using another
surface for reference

Note that we're using a true difference here, between data set values,
no translations, etc.

TODO: generalize this concept to allow transform functions which are
dependent on surfaces that are dependent on other surfaces, etc., as long
as the dependency doesn't loop back.

*/

#include <stdio.h>

#include <grass/gstypes.h>
#include "gsget.h"

static geosurf *Refsurf = NULL;
static typbuff *Refbuff = NULL;
static float Refscale = 1.0;

/***********************************************************************/
void gsdiff_set_SDscale(float scale)
{
    Refscale = scale;

    return;
}

/***********************************************************************/
float gsdiff_get_SDscale(void)
{
    return (Refscale);
}

/***********************************************************************/
void gsdiff_set_SDref(geosurf * gsref)
{
    Refsurf = gsref;
    Refbuff = gs_get_att_typbuff(gsref, ATT_TOPO, 0);

    return;
}

/***********************************************************************/
geosurf *gsdiff_get_SDref(void)
{
    if (Refsurf && Refbuff) {
	return (Refsurf);
    }

    return (NULL);
}

/***********************************************************************/
float gsdiff_do_SD(float val, int offset)
{
    float ref;

    if (Refbuff) {
	GET_MAPATT(Refbuff, offset, ref);
	return (ref + (val - ref) * Refscale);
    }

    return (val);
}