--- ray/src/rt/raytrace.c	1995/01/06 14:00:47	2.18
+++ ray/src/rt/raytrace.c	1997/03/07 16:58:54	2.28
@@ -1,4 +1,4 @@
-/* Copyright (c) 1994 Regents of the University of California */
+/* Copyright (c) 1996 Regents of the University of California */
 
 #ifndef lint
 static char SCCSid[] = "$SunId$ LBL";
@@ -24,7 +24,13 @@ extern CUBE  thescene;			/* our scene */
 extern int  maxdepth;			/* maximum recursion depth */
 extern double  minweight;		/* minimum ray weight */
 extern int  do_irrad;			/* compute irradiance? */
+extern COLOR  ambval;			/* ambient value */
 
+extern COLOR  cextinction;		/* global extinction coefficient */
+extern COLOR  salbedo;			/* global scattering albedo */
+extern double  seccg;			/* global scattering eccentricity */
+extern double  ssampdist;		/* scatter sampling distance */
+
 unsigned long  raynum = 0;		/* next unique ray number */
 unsigned long  nrays = 0;		/* number of calls to localhit */
 
@@ -55,21 +61,30 @@ double  rw;
 		r->rsrc = -1;
 		r->clipset = NULL;
 		r->revf = raytrace;
+		copycolor(r->cext, cextinction);
+		copycolor(r->albedo, salbedo);
+		r->gecc = seccg;
+		r->slights = NULL;
 	} else {				/* spawned ray */
 		r->rlvl = ro->rlvl;
 		if (rt & RAYREFL) {
 			r->rlvl++;
 			r->rsrc = -1;
 			r->clipset = ro->clipset;
+			r->rmax = 0.0;
 		} else {
 			r->rsrc = ro->rsrc;
 			r->clipset = ro->newcset;
+			r->rmax = ro->rmax <= FTINY ? 0.0 : ro->rmax - ro->rot;
 		}
 		r->revf = ro->revf;
+		copycolor(r->cext, ro->cext);
+		copycolor(r->albedo, ro->albedo);
+		r->gecc = ro->gecc;
+		r->slights = ro->slights;
 		r->rweight = ro->rweight * rw;
 		r->crtype = ro->crtype | (r->rtype = rt);
 		VCOPY(r->rorg, ro->rop);
-		r->rmax = 0.0;
 	}
 	rayclear(r);
 	return(r->rlvl <= maxdepth && r->rweight >= minweight ? 0 : -1);
@@ -81,6 +96,7 @@ register RAY  *r;
 {
 	r->rno = raynum++;
 	r->newcset = r->clipset;
+	r->robj = OVOID;
 	r->ro = NULL;
 	r->rot = FHUGE;
 	r->pert[0] = r->pert[1] = r->pert[2] = 0.0;
@@ -94,18 +110,16 @@ raytrace(r)			/* trace a ray and compute its value */
 RAY  *r;
 {
 	extern int  (*trace)();
-	int  gotmat;
 
 	if (localhit(r, &thescene))
-		gotmat = raycont(r);
+		raycont(r);		/* hit local surface, evaluate */
 	else if (r->ro == &Aftplane) {
-		r->ro = NULL;
+		r->ro = NULL;		/* hit aft clipping plane */
 		r->rot = FHUGE;
 	} else if (sourcehit(r))
-		gotmat = rayshade(r, r->ro->omod);
+		rayshade(r, r->ro->omod);	/* distant source */
 
-	if (r->ro != NULL && !gotmat)
-		objerror(r->ro, USER, "material not found");
+	rayparticipate(r);		/* for participating medium */
 
 	if (trace != NULL)
 		(*trace)(r);		/* trace execution */
@@ -116,11 +130,8 @@ raycont(r)			/* check for clipped object and continue 
 register RAY  *r;
 {
 	if ((r->clipset != NULL && inset(r->clipset, r->ro->omod)) ||
-			r->ro->omod == OVOID) {
+			!rayshade(r, r->ro->omod))
 		raytrans(r);
-		return(1);
-	}
-	return(rayshade(r, r->ro->omod));
 }
 
 
@@ -131,8 +142,6 @@ register RAY  *r;
 
 	if (rayorigin(&tr, r, TRANS, 1.0) == 0) {
 		VCOPY(tr.rdir, r->rdir);
-		if (r->rmax > FTINY)
-			tr.rmax = r->rmax - r->rot;
 		rayvalue(&tr);
 		copycolor(r->rcol, tr.rcol);
 		r->rt = r->rot + tr.rt;
@@ -177,6 +186,37 @@ int  mod;
 }
 
 
+rayparticipate(r)			/* compute ray medium participation */
+register RAY  *r;
+{
+	COLOR	ce, ca;
+	double	re, ge, be;
+
+	if (intens(r->cext) <= 1./FHUGE)
+		return;				/* no medium */
+	re = r->rot*colval(r->cext,RED);
+	ge = r->rot*colval(r->cext,GRN);
+	be = r->rot*colval(r->cext,BLU);
+	if (r->crtype & SHADOW) {		/* no scattering for sources */
+		re *= 1. - colval(r->albedo,RED);
+		ge *= 1. - colval(r->albedo,GRN);
+		be *= 1. - colval(r->albedo,BLU);
+	}
+	setcolor(ce,	re<=0. ? 1. : re>92. ? 0. : exp(-re),
+			ge<=0. ? 1. : ge>92. ? 0. : exp(-ge),
+			be<=0. ? 1. : be>92. ? 0. : exp(-be));
+	multcolor(r->rcol, ce);			/* path absorption */
+	if (r->crtype & SHADOW || intens(r->albedo) <= FTINY)
+		return;				/* no scattering */
+	setcolor(ca,
+		colval(r->albedo,RED)*colval(ambval,RED)*(1.-colval(ce,RED)),
+		colval(r->albedo,GRN)*colval(ambval,GRN)*(1.-colval(ce,GRN)),
+		colval(r->albedo,BLU)*colval(ambval,BLU)*(1.-colval(ce,BLU)));
+	addcolor(r->rcol, ca);			/* ambient in scattering */
+	srcscatter(r);				/* source in scattering */
+}
+
+
 raytexture(r, mod)			/* get material modifiers */
 RAY  *r;
 int  mod;
@@ -195,8 +235,11 @@ int  mod;
 			error(USER, errmsg);
 		}
 		******/
-		if ((*ofun[m->otype].funp)(m, r))
-			objerror(r->ro, USER, "conflicting materials");
+		if ((*ofun[m->otype].funp)(m, r)) {
+			sprintf(errmsg, "conflicting material \"%s\"",
+					m->oname);
+			objerror(r->ro, USER, errmsg);
+		}
 	}
 	depth--;			/* end here */
 }
@@ -210,31 +253,27 @@ double  coef;
 	RAY  fr, br;
 	int  foremat, backmat;
 	register int  i;
-					/* clip coefficient */
+					/* bound coefficient */
 	if (coef > 1.0)
 		coef = 1.0;
 	else if (coef < 0.0)
 		coef = 0.0;
 					/* compute foreground and background */
-	foremat = backmat = -1;
+	foremat = backmat = 0;
 					/* foreground */
 	copystruct(&fr, r);
-	if (fore != OVOID && coef > FTINY)
+	if (coef > FTINY)
 		foremat = rayshade(&fr, fore);
 					/* background */
 	copystruct(&br, r);
-	if (back != OVOID && coef < 1.0-FTINY)
+	if (coef < 1.0-FTINY)
 		backmat = rayshade(&br, back);
-					/* check */
-	if (foremat < 0)
-		if (backmat < 0)
-			foremat = backmat = 0;
+					/* check for transparency */
+	if (backmat ^ foremat)
+		if (backmat)
+			raytrans(&fr);
 		else
-			foremat = backmat;
-	else if (backmat < 0)
-		backmat = foremat;
-	if ((foremat==0) != (backmat==0))
-		objerror(r->ro, USER, "mixing material with non-material");
+			raytrans(&br);
 					/* mix perturbations */
 	for (i = 0; i < 3; i++)
 		r->pert[i] = coef*fr.pert[i] + (1.0-coef)*br.pert[i];
@@ -243,16 +282,31 @@ double  coef;
 	scalecolor(br.pcol, 1.0-coef);
 	copycolor(r->pcol, fr.pcol);
 	addcolor(r->pcol, br.pcol);
+					/* return value tells if material */
+	if (!foremat & !backmat)
+		return(0);
 					/* mix returned ray values */
-	if (foremat) {
-		scalecolor(fr.rcol, coef);
-		scalecolor(br.rcol, 1.0-coef);
-		copycolor(r->rcol, fr.rcol);
-		addcolor(r->rcol, br.rcol);
-		r->rt = bright(fr.rcol) > bright(br.rcol) ? fr.rt : br.rt;
+	scalecolor(fr.rcol, coef);
+	scalecolor(br.rcol, 1.0-coef);
+	copycolor(r->rcol, fr.rcol);
+	addcolor(r->rcol, br.rcol);
+	r->rt = bright(fr.rcol) > bright(br.rcol) ? fr.rt : br.rt;
+	return(1);
+}
+
+
+double
+raydist(r, flags)		/* compute (cumulative) ray distance */
+register RAY  *r;
+register int  flags;
+{
+	double  sum = 0.0;
+
+	while (r != NULL && r->crtype&flags) {
+		sum += r->rot;
+		r = r->parent;
 	}
-					/* return value tells if material */
-	return(foremat);
+	return(sum);
 }
 
 
@@ -396,8 +450,8 @@ register CUBE  *scene;
 			return(0);
 	}
 	cxset[0] = 0;
-	return(raymove(curpos, cxset, sflags, r, scene) == RAYHIT &&
-			r->ro != &Aftplane);
+	raymove(curpos, cxset, sflags, r, scene);
+	return(r->ro != NULL & r->ro != &Aftplane);
 }
 
 
@@ -501,7 +555,8 @@ OBJECT  *cxs;
 	checkset(oset, cxs);			/* eliminate double-checking */
 	for (i = oset[0]; i > 0; i--) {
 		o = objptr(oset[i]);
-		(*ofun[o->otype].funp)(o, r);
+		if ((*ofun[o->otype].funp)(o, r))
+			r->robj = oset[i];
 	}
 	if (r->ro == NULL)
 		return(0);			/* no scores yet */