/* Copyright (c) 1995 Regents of the University of California */

#ifndef lint
static char SCCSid[] = "$SunId$ LBL";
#endif

/*
 * Mist volumetric material.
 */

#include  "ray.h"

#include  "source.h"

/*
 *  A mist volume is used to specify a region in the scene where a certain
 *  light source (or sources) is going to contribute to scattering.  The
 *  material can add to the existing global medium, and override any ray
 *  settings for scattering albedo and eccentricity.  Overlapping mist
 *  regions should agree w.r.t. albedo and eccentricity, and
 *  should have disjoint source lists.
 *
 *  A pattern, if used, should compute the line integral of extinction,
 *  and will modify the first three arguments directly.  This will tend
 *  to invalidate results when there are other objects intersected within
 *  the mist region.
 *
 *  The string arguments for MAT_MIST are the identifiers for the important
 *  light sources, which will be looked up in the source array.  The last
 *  source found matching a name is the one used.  A relayed light source
 *  may be indicated by the relay surface name, followed by a '>' character,
 *  followed by the relayed source name (which may be another relay).
 *
 *  Up to five real arguments may be given for MAT_MIST:
 *
 *	[ext_r  ext_g  ext_b  [albedo [gecc]]]
 *
 *  The primaries indicate medium extinction per unit length (absorption
 *  plus scattering).  The albedo is the ratio of scattering to extinction,
 *  and is set globally by the -ma option (salbedo) and overridden here.
 *  The Heyney-Greenstein eccentricity parameter (-mg seccg) indicates how much
 *  scattering favors the forward direction.  A value of 0 means isotropic
 *  scattering.  A value approaching 1 indicates strong forward scattering.
 */

#define RELAYDELIM	'>'		/* relay delimiter character */

extern COLOR  cextinction;		/* global coefficient of extinction */
extern double  salbedo;			/* global scattering albedo */
extern double  seccg;			/* global scattering eccentricity */


static int
inslist(sl, n)		/* return index of source n if it's in list sl */
register int  *sl;
register int  n;
{
	register int  i;

	for (i = sl[0]; i > 0; i--)
		if (sl[i] == n)
			return(i);
	return(0);
}


static int
srcmatch(sp, id)	/* check for an id match on a light source */
register SRCREC  *sp;
register char  *id;
{
	extern char  *index();
	register char  *cp;
						/* check for relay sources */
	while ((cp = index(id, RELAYDELIM)) != NULL) {
		if (!(sp->sflags & SVIRTUAL) || sp->so == NULL)
			return(0);
		if (strncmp(id, sp->so->oname, cp-id) || sp->so->oname[cp-id])
			return(0);
		id = cp + 1;				/* relay to next */
		sp = source + sp->sa.sv.sn;
	}
	if (sp->sflags & SVIRTUAL || sp->so == NULL)
		return(0);
	return(!strcmp(id, sp->so->oname));
}


static
add2slist(r, sl)	/* add source list to ray's */
register RAY  *r;
register int  *sl;
{
	static int  slspare[MAXSLIST+1];	/* in case of emergence */
	register int  i;

	if (sl == NULL || sl[0] == 0)		/* nothing to add */
		return;
	if (r->slights == NULL)
		(r->slights = slspare)[0] = 0;	/* just once per ray path */
	for (i = sl[0]; i > 0; i--)
		if (!inslist(r->slights, sl[i])) {
			if (r->slights[0] >= MAXSLIST)
				error(USER, "scattering source list overflow");
			r->slights[++r->slights[0]] = sl[i];
		}
}


m_mist(m, r)		/* process a ray entering or leaving some mist */
OBJREC  *m;
register RAY  *r;
{
	RAY  p;
	int  *myslist = NULL;
	int  newslist[MAXSLIST+1];
	COLOR  mext;
	double  re, ge, be;
	register int  i, j;
					/* check arguments */
	if (m->oargs.nfargs > 5)
		objerror(m, USER, "bad arguments");
					/* get source indices */
	if (m->oargs.nsargs > 0 && (myslist = (int *)m->os) == NULL) {
		if (m->oargs.nsargs > MAXSLIST)
			objerror(m, USER, "too many sources in list");
		myslist = (int *)malloc((m->oargs.nsargs+1)*sizeof(int));
		if (myslist == NULL)
			goto memerr;
		myslist[0] = 0;			/* size is first in list */
		for (j = 0; j < m->oargs.nsargs; j++) {
			i = nsources;		/* look up each source id */
			while (i--)
				if (srcmatch(source+i, m->oargs.sarg[j]))
					break;
			if (i < 0) {
				sprintf(errmsg, "unknown source \"%s\"",
						m->oargs.sarg[j]);
				objerror(m, WARNING, errmsg);
			} else if (inslist(myslist, i)) {
				sprintf(errmsg, "duplicate source \"%s\"",
						m->oargs.sarg[j]);
				objerror(m, WARNING, errmsg);
			} else
				myslist[++myslist[0]] = i;
		}
		m->os = (char *)myslist;
	}
	if (m->oargs.nfargs > 2) {		/* compute extinction */
		setcolor(mext, m->oargs.farg[0], m->oargs.farg[1],
				m->oargs.farg[2]);
		raytexture(r, m->omod);			/* get modifiers */
		multcolor(mext, r->pcol);
	} else
		setcolor(mext, 0., 0., 0.);
						/* start transmitted ray */
	if (rayorigin(&p, r, TRANS, 1.) < 0)
		return(1);
	VCOPY(p.rdir, r->rdir);
	p.slights = newslist;
	if (r->slights != NULL)			/* copy old list if one */
		for (j = r->slights[0]; j >= 0; j--)
			p.slights[j] = r->slights[j];
	else
		p.slights[0] = 0;
	if (r->rod > 0.) {			/* entering ray */
		addcolor(p.cext, mext);
		if (m->oargs.nfargs > 3)
			p.albedo = m->oargs.farg[3];
		if (m->oargs.nfargs > 4)
			p.gecc = m->oargs.farg[4];
		add2slist(&p, myslist);			/* add to list */
	} else {				/* leaving ray */
		if (myslist != NULL) {			/* delete from list */
			for (j = myslist[0]; j > 0; j--)
				if (i = inslist(p.slights, myslist[j]))
					p.slights[i] = -1;
			for (i = 0, j = 1; j <= p.slights[0]; j++)
				if (p.slights[j] != -1)
					p.slights[++i] = p.slights[j];
			if (p.slights[0] - i < myslist[0]) {	/* fix old */
				addcolor(r->cext, mext);
				if (m->oargs.nfargs > 3)
					r->albedo = m->oargs.farg[3];
				if (m->oargs.nfargs > 4)
					r->gecc = m->oargs.farg[4];
				add2slist(r, myslist);
			}
			p.slights[0] = i;
		}
		re = colval(r->cext,RED) - colval(mext,RED);
		ge = colval(r->cext,GRN) - colval(mext,GRN);
		be = colval(r->cext,BLU) - colval(mext,BLU);
		setcolor(p.cext, re<0. ? 0. : re,
				ge<0. ? 0. : ge,
				be<0. ? 0. : be);
		if (m->oargs.nfargs > 3)
			p.albedo = salbedo;
		if (m->oargs.nfargs > 4)
			p.gecc = seccg;
	}
	rayvalue(&p);				/* calls rayparticipate() */
	copycolor(r->rcol, p.rcol);		/* return value */
	r->rt = r->rot + p.rt;
	return(1);
memerr:
	error(SYSTEM, "out of memory in m_mist");
}