--- ray/src/rt/m_bsdf.c	2020/07/09 17:32:31	2.61
+++ ray/src/rt/m_bsdf.c	2021/08/27 03:09:27	2.65
@@ -1,5 +1,5 @@
 #ifndef lint
-static const char RCSid[] = "$Id: m_bsdf.c,v 2.61 2020/07/09 17:32:31 greg Exp $";
+static const char RCSid[] = "$Id: m_bsdf.c,v 2.65 2021/08/27 03:09:27 greg Exp $";
 #endif
 /*
  *  Shading for materials with BSDFs taken from XML data files
@@ -17,7 +17,7 @@ static const char RCSid[] = "$Id: m_bsdf.c,v 2.61 2020
 #include  "pmapmat.h"
 
 /*
-  *	Arguments to this material include optional diffuse colors.
+ *	Arguments to this material include optional diffuse colors.
  *  String arguments include the BSDF and function files.
  *	For the MAT_BSDF type, a non-zero thickness causes the useful behavior
  *  of translating transmitted rays this distance beneath the surface
@@ -130,7 +130,6 @@ compute_through(BSDFDAT *ndp)
 					{1.8, -1.8}, {-2.4, 0}, {0, 2.4},
 					{0, -2.4}, {2.4, 0},
 				};
-	const double	peak_over = 1.5;
 	PEAKSAMP	psamp[NDIR2CHECK];
 	SDSpectralDF	*dfp;
 	FVECT		pdir;
@@ -165,7 +164,7 @@ compute_through(BSDFDAT *ndp)
 	}
 	qsort(psamp, NDIR2CHECK, sizeof(PEAKSAMP), cmp_psamp);
 	if (psamp[0].vy <= FTINY)
-		return;				/* zero area */
+		return;				/* zero BTDF here */
 	setcolor(vpeak, 0, 0, 0);
 	setcolor(vsurr, 0, 0, 0);
 	vypeak = tomsum = tomsurr = 0;		/* combine top unique values */
@@ -178,32 +177,31 @@ compute_through(BSDFDAT *ndp)
 						SDqueryMin, ndp->sd);
 		if (ec)
 			goto baderror;
-						/* not really a peak? */
+
+		scalecolor(psamp[i].vcol, tomega);
+						/* not part of peak? */
 		if (tomega > 1.5*dfp->minProjSA ||
 					vypeak > 8.*psamp[i].vy*ns) {
 			if (!i) return;		/* abort */
-			scalecolor(psamp[i].vcol, tomega);
 			addcolor(vsurr, psamp[i].vcol);
 			tomsurr += tomega;
 			continue;
 		}
-		scalecolor(psamp[i].vcol, tomega);
 		addcolor(vpeak, psamp[i].vcol);
 		tomsum += tomega;
 		vypeak += psamp[i].vy;
 		++ns;
 	}
-	if (vypeak*tomsurr < peak_over*bright(vsurr)*ns)
-		return;				/* peak not peaky enough */
-	if ((vypeak/ns - ndp->sd->tLamb.cieY*(1./PI))*tomsum <= .001)
-		return;				/* < 0.1% transmission */
+	if (tomsurr <= FTINY)			/* no surround implies no peak */
+		return;
+	if ((vypeak/ns - (ndp->vray[2] > 0 ? ndp->sd->tLambFront.cieY
+			: ndp->sd->tLambBack.cieY)*(1./PI))*tomsum < .0005)
+		return;				/* < 0.05% transmission */
 	copycolor(ndp->cthru, vpeak);		/* already scaled by omega */
 	multcolor(ndp->cthru, ndp->pr->pcol);	/* modify by pattern */
-	if (tomsurr > FTINY) {			/* surround contribution? */
-		scalecolor(vsurr, 1./tomsurr);	/* this one is avg. BTDF */
-		copycolor(ndp->cthru_surr, vsurr);
-		multcolor(ndp->cthru_surr, ndp->pr->pcol);
-	}
+	scalecolor(vsurr, 1./tomsurr);		/* surround is avg. BTDF */
+	copycolor(ndp->cthru_surr, vsurr);
+	multcolor(ndp->cthru_surr, ndp->pr->pcol);
 	return;
 baderror:
 	objerror(ndp->mp, USER, transSDError(ec));
@@ -255,11 +253,16 @@ direct_specular_OK(COLOR cval, FVECT ldir, double omeg
 			return(0);	/* all diffuse */
 		sv = ndp->sd->rLambBack;
 		break;
-	default:
+	case 1:
 		if ((ndp->sd->tf == NULL) & (ndp->sd->tb == NULL))
 			return(0);	/* all diffuse */
-		sv = ndp->sd->tLamb;
+		sv = ndp->sd->tLambFront;
 		break;
+	case 2:
+		if ((ndp->sd->tf == NULL) & (ndp->sd->tb == NULL))
+			return(0);	/* all diffuse */
+		sv = ndp->sd->tLambBack;
+		break;
 	}
 	if (sv.cieY > FTINY) {
 		diffY = sv.cieY *= 1./PI;
@@ -677,7 +680,7 @@ m_bsdf(OBJREC *m, RAY *r)
 		SDfreeCache(nd.sd);
 		return(1);
 	}
-						/* diffuse reflectance */
+						/* diffuse components */
 	if (hitfront) {
 		cvt_sdcolor(nd.rdiff, &nd.sd->rLambFront);
 		if (m->oargs.nfargs >= 3) {
@@ -686,6 +689,7 @@ m_bsdf(OBJREC *m, RAY *r)
 					m->oargs.farg[2]);
 			addcolor(nd.rdiff, ctmp);
 		}
+		cvt_sdcolor(nd.tdiff, &nd.sd->tLambFront);
 	} else {
 		cvt_sdcolor(nd.rdiff, &nd.sd->rLambBack);
 		if (m->oargs.nfargs >= 6) {
@@ -694,10 +698,9 @@ m_bsdf(OBJREC *m, RAY *r)
 					m->oargs.farg[5]);
 			addcolor(nd.rdiff, ctmp);
 		}
+		cvt_sdcolor(nd.tdiff, &nd.sd->tLambBack);
 	}
-						/* diffuse transmittance */
-	cvt_sdcolor(nd.tdiff, &nd.sd->tLamb);
-	if (m->oargs.nfargs >= 9) {
+	if (m->oargs.nfargs >= 9) {		/* add diffuse transmittance? */
 		setcolor(ctmp, m->oargs.farg[6],
 				m->oargs.farg[7],
 				m->oargs.farg[8]);