--- ray/src/rt/raytrace.c	1993/12/09 09:34:08	2.8
+++ ray/src/rt/raytrace.c	1996/03/21 15:33:05	2.24
@@ -1,4 +1,4 @@
-/* Copyright (c) 1991 Regents of the University of California */
+/* Copyright (c) 1995 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 double  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 */
 
@@ -34,6 +40,8 @@ OBJREC  Lamb = {
 	{0, 5, NULL, Lambfa}, NULL,
 };					/* a Lambertian surface */
 
+OBJREC  Aftplane;			/* aft clipping plane object */
+
 static int  raymove(), checkset(), checkhit();
 
 #define  MAXLOOP	128		/* modifier loop detection */
@@ -53,17 +61,27 @@ double  rw;
 		r->rsrc = -1;
 		r->clipset = NULL;
 		r->revf = raytrace;
+		copycolor(r->cext, cextinction);
+		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);
+		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);
@@ -93,10 +111,15 @@ RAY  *r;
 	extern int  (*trace)();
 
 	if (localhit(r, &thescene))
-		raycont(r);
-	else if (sourcehit(r))
-		rayshade(r, r->ro->omod);
+		raycont(r);		/* hit local surface, evaluate */
+	else if (r->ro == &Aftplane) {
+		r->ro = NULL;		/* hit aft clipping plane */
+		r->rot = FHUGE;
+	} else if (sourcehit(r))
+		rayshade(r, r->ro->omod);	/* distant source */
 
+	rayparticipate(r);		/* for participating medium */
+
 	if (trace != NULL)
 		(*trace)(r);		/* trace execution */
 }
@@ -106,10 +129,8 @@ 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);
-	else
-		rayshade(r, r->ro->omod);
 }
 
 
@@ -132,12 +153,13 @@ register RAY  *r;
 int  mod;
 {
 	static int  depth = 0;
+	int  gotmat;
 	register OBJREC  *m;
 					/* check for infinite loop */
 	if (depth++ >= MAXLOOP)
 		objerror(r->ro, USER, "possible modifier loop");
 	r->rt = r->rot;			/* set effective ray length */
-	for ( ; mod != OVOID; mod = m->omod) {
+	for (gotmat = 0; !gotmat && mod != OVOID; mod = m->omod) {
 		m = objptr(mod);
 		/****** unnecessary test since modifier() is always called
 		if (!ismodifier(m->otype)) {
@@ -150,21 +172,51 @@ int  mod;
 			if (irr_ignore(m->otype)) {
 				depth--;
 				raytrans(r);
-				return;
+				return(1);
 			}
 			if (!islight(m->otype))
 				m = &Lamb;
 		}
-		(*ofun[m->otype].funp)(m, r);	/* execute function */
-		if (ismaterial(m->otype)) {	/* materials call raytexture */
-			depth--;
-			return;		/* we're done */
-		}
+					/* materials call raytexture */
+		gotmat = (*ofun[m->otype].funp)(m, r);
 	}
-	objerror(r->ro, USER, "material not found");
+	depth--;
+	return(gotmat);
 }
 
 
+rayparticipate(r)			/* compute ray medium participation */
+register RAY  *r;
+{
+	COLOR	ce, ca;
+	double	dist;
+	double	re, ge, be;
+
+	if (intens(r->cext) <= 1./FHUGE)
+		return;				/* no medium */
+	if ((dist = r->rot) >= FHUGE)
+		dist = 2.*thescene.cusize;	/* what to use for infinity? */
+	if (r->crtype & SHADOW)
+		dist *= 1. - salbedo;		/* no scattering for sources */
+	if (dist <= FTINY)
+		return;				/* no effective ray travel */
+	re = dist*colval(r->cext,RED);
+	ge = dist*colval(r->cext,GRN);
+	be = dist*colval(r->cext,BLU);
+	setcolor(ce,	re>92. ? 0. : exp(-re),
+			ge>92. ? 0. : exp(-ge),
+			be>92. ? 0. : exp(-be));
+	multcolor(r->rcol, ce);			/* path absorption */
+	if (r->albedo <= FTINY || r->crtype & SHADOW)
+		return;				/* no scattering */
+	setcolor(ca,	salbedo*colval(ambval,RED)*(1.-colval(ce,RED)),
+			salbedo*colval(ambval,GRN)*(1.-colval(ce,GRN)),
+			salbedo*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;
@@ -177,11 +229,17 @@ int  mod;
 					/* execute textures and patterns */
 	for ( ; mod != OVOID; mod = m->omod) {
 		m = objptr(mod);
-		if (!istexture(m->otype)) {
+		/****** unnecessary test since modifier() is always called
+		if (!ismodifier(m->otype)) {
 			sprintf(errmsg, "illegal modifier \"%s\"", m->oname);
 			error(USER, errmsg);
 		}
-		(*ofun[m->otype].funp)(m, r);
+		******/
+		if ((*ofun[m->otype].funp)(m, r)) {
+			sprintf(errmsg, "conflicting material \"%s\"",
+					m->oname);
+			objerror(r->ro, USER, errmsg);
+		}
 	}
 	depth--;			/* end here */
 }
@@ -192,48 +250,67 @@ register RAY  *r;
 OBJECT  fore, back;
 double  coef;
 {
-	FVECT  curpert, forepert, backpert;
-	COLOR  curpcol, forepcol, backpcol;
+	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;
-					/* save current mods */
-	VCOPY(curpert, r->pert);
-	copycolor(curpcol, r->pcol);
-					/* compute new mods */
-						/* foreground */
-	r->pert[0] = r->pert[1] = r->pert[2] = 0.0;
-	setcolor(r->pcol, 1.0, 1.0, 1.0);
-	if (fore != OVOID && coef > FTINY)
-		raytexture(r, fore);
-	VCOPY(forepert, r->pert);
-	copycolor(forepcol, r->pcol);
-						/* background */
-	r->pert[0] = r->pert[1] = r->pert[2] = 0.0;
-	setcolor(r->pcol, 1.0, 1.0, 1.0);
-	if (back != OVOID && coef < 1.0-FTINY)
-		raytexture(r, back);
-	VCOPY(backpert, r->pert);
-	copycolor(backpcol, r->pcol);
-					/* sum perturbations */
+					/* compute foreground and background */
+	foremat = backmat = 0;
+					/* foreground */
+	copystruct(&fr, r);
+	if (coef > FTINY)
+		foremat = rayshade(&fr, fore);
+					/* background */
+	copystruct(&br, r);
+	if (coef < 1.0-FTINY)
+		backmat = rayshade(&br, back);
+					/* check for transparency */
+	if (backmat ^ foremat)
+		if (backmat)
+			raytrans(&fr);
+		else
+			raytrans(&br);
+					/* mix perturbations */
 	for (i = 0; i < 3; i++)
-		r->pert[i] = curpert[i] + coef*forepert[i] +
-				(1.0-coef)*backpert[i];
-					/* multiply colors */
-	setcolor(r->pcol, coef*colval(forepcol,RED) +
-				(1.0-coef)*colval(backpcol,RED),
-			coef*colval(forepcol,GRN) +
-				(1.0-coef)*colval(backpcol,GRN),
-			coef*colval(forepcol,BLU) +
-				(1.0-coef)*colval(backpcol,BLU));
-	multcolor(r->pcol, curpcol);
+		r->pert[i] = coef*fr.pert[i] + (1.0-coef)*br.pert[i];
+					/* mix pattern colors */
+	scalecolor(fr.pcol, 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 */
+	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(sum);
+}
+
+
+double
 raynormal(norm, r)		/* compute perturbed normal for ray */
 FVECT  norm;
 register RAY  *r;
@@ -338,6 +415,14 @@ register CUBE  *scene;
 	}
 	if (sflags == 0)
 		error(CONSISTENCY, "zero ray direction in localhit");
+					/* start off assuming nothing hit */
+	if (r->rmax > FTINY) {		/* except aft plane if one */
+		r->ro = &Aftplane;
+		r->rot = r->rmax;
+		for (i = 0; i < 3; i++)
+			r->rop[i] = r->rorg[i] + r->rot*r->rdir[i];
+	}
+					/* find global cube entrance point */
 	t = 0.0;
 	if (!incube(scene, curpos)) {
 					/* find distance to entry */
@@ -355,6 +440,8 @@ register CUBE  *scene;
 				t = dt;	/* farthest face is the one */
 		}
 		t += FTINY;		/* fudge to get inside cube */
+		if (t >= r->rot)	/* clipped already */
+			return(0);
 					/* advance position */
 		for (i = 0; i < 3; i++)
 			curpos[i] += r->rdir[i]*t;
@@ -363,7 +450,8 @@ register CUBE  *scene;
 			return(0);
 	}
 	cxset[0] = 0;
-	return(raymove(curpos, cxset, sflags, r, scene) == RAYHIT);
+	raymove(curpos, cxset, sflags, r, scene);
+	return(r->ro != NULL & r->ro != &Aftplane);
 }
 
 
@@ -418,7 +506,10 @@ register CUBE  *cu;
 		}
 		/*NOTREACHED*/
 	}
-	if (isfull(cu->cutree) && checkhit(r, cu, cxs))
+	if (isfull(cu->cutree)) {
+		if (checkhit(r, cu, cxs))
+			return(RAYHIT);
+	} else if (r->ro == &Aftplane && incube(cu, r->rop))
 		return(RAYHIT);
 					/* advance to next cube */
 	if (dirf&0x11) {