--- ray/src/rt/dielectric.c	1995/12/08 18:22:07	2.9
+++ ray/src/rt/dielectric.c	1996/07/11 15:14:05	2.12
@@ -51,16 +51,28 @@ static int  lambda();
 #define  MINCOS		0.997		/* minimum dot product for dispersion */
 
 extern COLOR  cextinction;		/* global coefficient of extinction */
-extern double  salbedo;			/* global scattering albedo */
+extern COLOR  salbedo;			/* global scattering albedo */
 
 
+static double
+mylog(x)		/* special log for extinction coefficients */
+double  x;
+{
+	if (x < 1e-40)
+		return(-100.);
+	if (x >= 1.)
+		return(0.);
+	return(log(x));
+}
+
+
 m_dielectric(m, r)	/* color a ray which hit a dielectric interface */
 OBJREC  *m;
 register RAY  *r;
 {
 	double  cos1, cos2, nratio;
 	COLOR  ctrans;
-	double  talb;
+	COLOR  talb;
 	double  mabsorp;
 	double  refl, trans;
 	FVECT  dnorm;
@@ -85,38 +97,45 @@ register RAY  *r;
 		dnorm[0] = -dnorm[0];
 		dnorm[1] = -dnorm[1];
 		dnorm[2] = -dnorm[2];
-		setcolor(r->cext, -log(m->oargs.farg[0]*colval(r->pcol,RED)),
-				 -log(m->oargs.farg[1]*colval(r->pcol,GRN)),
-				 -log(m->oargs.farg[2]*colval(r->pcol,BLU)));
-		r->albedo = 0.;
+		setcolor(r->cext, -mylog(m->oargs.farg[0]*colval(r->pcol,RED)),
+				 -mylog(m->oargs.farg[1]*colval(r->pcol,GRN)),
+				 -mylog(m->oargs.farg[2]*colval(r->pcol,BLU)));
+		setcolor(r->albedo, 0., 0., 0.);
 		r->gecc = 0.;
 		if (m->otype == MAT_INTERFACE) {
 			setcolor(ctrans,
-				-log(m->oargs.farg[4]*colval(r->pcol,RED)),
-				-log(m->oargs.farg[5]*colval(r->pcol,GRN)),
-				-log(m->oargs.farg[6]*colval(r->pcol,BLU)));
-			talb = 0.;
+				-mylog(m->oargs.farg[4]*colval(r->pcol,RED)),
+				-mylog(m->oargs.farg[5]*colval(r->pcol,GRN)),
+				-mylog(m->oargs.farg[6]*colval(r->pcol,BLU)));
+			setcolor(talb, 0., 0., 0.);
 		} else {
 			copycolor(ctrans, cextinction);
-			talb = salbedo;
+			copycolor(talb, salbedo);
 		}
 	} else {				/* outside */
 		nratio = 1.0 / nratio;
 
-		setcolor(ctrans, -log(m->oargs.farg[0]*colval(r->pcol,RED)),
-				 -log(m->oargs.farg[1]*colval(r->pcol,GRN)),
-				 -log(m->oargs.farg[2]*colval(r->pcol,BLU)));
-		talb = 0.;
+		setcolor(ctrans, -mylog(m->oargs.farg[0]*colval(r->pcol,RED)),
+				 -mylog(m->oargs.farg[1]*colval(r->pcol,GRN)),
+				 -mylog(m->oargs.farg[2]*colval(r->pcol,BLU)));
+		setcolor(talb, 0., 0., 0.);
 		if (m->otype == MAT_INTERFACE) {
 			setcolor(r->cext,
-				-log(m->oargs.farg[4]*colval(r->pcol,RED)),
-				-log(m->oargs.farg[5]*colval(r->pcol,GRN)),
-				-log(m->oargs.farg[6]*colval(r->pcol,BLU)));
-			r->albedo = 0.;
+				-mylog(m->oargs.farg[4]*colval(r->pcol,RED)),
+				-mylog(m->oargs.farg[5]*colval(r->pcol,GRN)),
+				-mylog(m->oargs.farg[6]*colval(r->pcol,BLU)));
+			setcolor(r->albedo, 0., 0., 0.);
 			r->gecc = 0.;
 		}
 	}
-	mabsorp = exp(-bright(r->cext)*r->rot);		/* approximate */
+						/* estimate absorption */
+	mabsorp = colval(r->cext,RED) < colval(r->cext,GRN) ?
+			colval(r->cext,RED) : colval(r->cext,GRN);
+	if (colval(r->cext,BLU) < mabsorp) mabsorp = colval(r->cext,BLU);
+	if (mabsorp > 0.)
+		mabsorp = exp(-mabsorp*r->rot);		/* conservative */
+	else
+		mabsorp = 1.0;
 
 	d2 = 1.0 - nratio*nratio*(1.0 - cos1*cos1);	/* compute cos theta2 */
 
@@ -153,11 +172,12 @@ register RAY  *r;
 					|| r->crtype & SHADOW
 					|| !directvis
 					|| m->oargs.farg[4] == 0.0
-					|| !disperse(m, r, p.rdir, trans))
+					|| !disperse(m, r, p.rdir,
+							trans, ctrans, talb))
 #endif
 			{
 				copycolor(p.cext, ctrans);
-				p.albedo = talb;
+				copycolor(p.albedo, talb);
 				rayvalue(&p);
 				scalecolor(p.rcol, trans);
 				addcolor(r->rcol, p.rcol);
@@ -187,11 +207,12 @@ register RAY  *r;
 #ifdef  DISPERSE
 
 static
-disperse(m, r, vt, tr)		/* check light sources for dispersion */
+disperse(m, r, vt, tr, cet, abt)  /* check light sources for dispersion */
 OBJREC  *m;
 RAY  *r;
 FVECT  vt;
 double  tr;
+COLOR  cet, abt;
 {
 	RAY  sray, *entray;
 	FVECT  v1, v2, n1, n2;
@@ -277,6 +298,8 @@ double  tr;
 		if (l1 > MAXLAMBDA || l1 < MINLAMBDA)	/* not visible */
 			continue;
 						/* trace source ray */
+		copycolor(sray.cext, cet);
+		copycolor(sray.albedo, abt);
 		normalize(sray.rdir);
 		rayvalue(&sray);
 		if (bright(sray.rcol) <= FTINY)	/* missed it */