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m_mist.c
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Wed, May 22, 11:41

m_mist.c
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#ifndef lint
static const char RCSid[] = "$Id: m_mist.c,v 2.20 2019/02/13 02:38:26 greg Exp $";
#endif
/*
* Mist volumetric material.
*/
#include "copyright.h"
#include <string.h>
#include "ray.h"
#include "source.h"
#include "rtotypes.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_r albedo_g albedo_b [gecc]]]
*
* The primaries indicate medium extinction per unit length (absorption
* plus scattering), which is added to the global extinction coefficient, set
* by the -me option. 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.
*/
#ifndef MAXSLIST
#define MAXSLIST 32 /* maximum sources to check */
#endif
#define RELAYDELIM '>' /* relay delimiter character */
static int inslist(int *sl, int n);
static int srcmatch(SRCREC *sp, char *id);
static void add2slist(RAY *r, int *sl);
static int
inslist( /* return index of source n if it's in list sl */
int *sl,
int n
)
{
int i;
for (i = sl[0]; i > 0; i--)
if (sl[i] == n)
return(i);
return(0);
}
static int
srcmatch( /* check for an id match on a light source */
SRCREC *sp,
char *id
)
{
char *cp;
/* check for relay sources */
while ((cp = strchr(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 void
add2slist( /* add source list to ray's */
RAY *r,
int *sl
)
{
static int slspare[MAXSLIST+1]; /* in case of emergence */
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(INTERNAL,
"scattering source list overflow");
r->slights[++r->slights[0]] = sl[i];
}
}
int
m_mist( /* process a ray entering or leaving some mist */
OBJREC *m,
RAY *r
)
{
RAY p;
int *myslist = NULL;
int newslist[MAXSLIST+1];
COLOR mext;
double re, ge, be;
int i, j;
/* check arguments */
if (m->oargs.nfargs > 7)
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, INTERNAL, "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, TRANS, r, NULL) < 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 > 5)
setcolor(p.albedo, m->oargs.farg[3],
m->oargs.farg[4], m->oargs.farg[5]);
if (m->oargs.nfargs > 6)
p.gecc = m->oargs.farg[6];
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 > 5)
setcolor(r->albedo, m->oargs.farg[3],
m->oargs.farg[4], m->oargs.farg[5]);
if (m->oargs.nfargs > 6)
r->gecc = m->oargs.farg[6];
add2slist(r, myslist);
}
p.slights[0] = i;
}
if ((re = colval(r->cext,RED) - colval(mext,RED)) <
colval(cextinction,RED))
re = colval(cextinction,RED);
if ((ge = colval(r->cext,GRN) - colval(mext,GRN)) <
colval(cextinction,GRN))
ge = colval(cextinction,GRN);
if ((be = colval(r->cext,BLU) - colval(mext,BLU)) <
colval(cextinction,BLU))
be = colval(cextinction,BLU);
setcolor(p.cext, re, ge, be);
if (m->oargs.nfargs > 5)
copycolor(p.albedo, salbedo);
if (m->oargs.nfargs > 6)
p.gecc = seccg;
}
rayvalue(&p); /* calls rayparticipate() */
copycolor(r->rcol, p.rcol); /* return value */
copycolor(r->mcol, p.mcol);
r->rmt = r->rot + p.rmt;
r->rxt = r->rot + p.rxt;
return(1);
memerr:
error(SYSTEM, "out of memory in m_mist");
return 0; /* pro forma return */
}

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