--- ray/src/rt/dielectric.c	2003/02/25 02:47:22	2.16
+++ ray/src/rt/dielectric.c	2004/09/09 06:46:07	2.19
@@ -1,5 +1,5 @@
 #ifndef lint
-static const char	RCSid[] = "$Id: dielectric.c,v 2.16 2003/02/25 02:47:22 greg Exp $";
+static const char	RCSid[] = "$Id: dielectric.c,v 2.19 2004/09/09 06:46:07 greg Exp $";
 #endif
 /*
  *  dielectric.c - shading function for transparent materials.
@@ -8,15 +8,18 @@ static const char	RCSid[] = "$Id: dielectric.c,v 2.16 
 #include "copyright.h"
 
 #include  "ray.h"
-
 #include  "otypes.h"
+#include  "rtotypes.h"
 
 #ifdef  DISPERSE
 #include  "source.h"
-static  disperse();
-static int  lambda();
+static int disperse(OBJREC *m,RAY *r,FVECT vt,double tr,COLOR cet,COLOR abt);
+static int lambda(OBJREC  *m, FVECT  v2, FVECT  dv, FVECT  lr);
 #endif
 
+static double mylog(double  x);
+
+
 /*
  *     Explicit calculations for Fresnel's equation are performed,
  *  but only one square root computation is necessary.
@@ -49,8 +52,9 @@ static int  lambda();
 
 
 static double
-mylog(x)		/* special log for extinction coefficients */
-double  x;
+mylog(		/* special log for extinction coefficients */
+	double  x
+)
 {
 	if (x < 1e-40)
 		return(-100.);
@@ -60,14 +64,19 @@ double  x;
 }
 
 
-m_dielectric(m, r)	/* color a ray which hit a dielectric interface */
-OBJREC  *m;
-register RAY  *r;
+extern int
+m_dielectric(	/* color a ray which hit a dielectric interface */
+	OBJREC  *m,
+	register RAY  *r
+)
 {
 	double  cos1, cos2, nratio;
 	COLOR  ctrans;
 	COLOR  talb;
 	int  hastexture;
+	double  transdist, transtest=0;
+	double  mirdist, mirtest=0;
+	int	flatsurface;
 	double  refl, trans;
 	FVECT  dnorm;
 	double  d1, d2;
@@ -79,12 +88,14 @@ register RAY  *r;
 
 	raytexture(r, m->omod);			/* get modifiers */
 
-	if (hastexture = DOT(r->pert,r->pert) > FTINY*FTINY)
+	if ( (hastexture = DOT(r->pert,r->pert) > FTINY*FTINY) )
 		cos1 = raynormal(dnorm, r);	/* perturb normal */
 	else {
 		VCOPY(dnorm, r->ron);
 		cos1 = r->rod;
 	}
+	flatsurface = !hastexture && r->ro != NULL && isflat(r->ro->otype);
+
 						/* index of refraction */
 	if (m->otype == MAT_DIELECTRIC)
 		nratio = m->oargs.farg[3] + m->oargs.farg[4]/MLAMBDA;
@@ -183,8 +194,13 @@ register RAY  *r;
 				rayvalue(&p);
 				scalecolor(p.rcol, trans);
 				addcolor(r->rcol, p.rcol);
-				if (nratio >= 1.0-FTINY && nratio <= 1.0+FTINY)
-					r->rt = r->rot + p.rt;
+						/* virtual distance */
+				if (flatsurface ||
+					(1.-FTINY <= nratio &&
+						nratio <= 1.+FTINY)) {
+					transtest = 2*bright(p.rcol);
+					transdist = r->rot + p.rt;
+				}
 			}
 		}
 	}
@@ -204,7 +220,18 @@ register RAY  *r;
 
 		scalecolor(p.rcol, refl);	/* color contribution */
 		addcolor(r->rcol, p.rcol);
+						/* virtual distance */
+		if (flatsurface) {
+			mirtest = 2*bright(p.rcol);
+			mirdist = r->rot + p.rt;
+		}
 	}
+				/* check distance to return */
+	d1 = bright(r->rcol);
+	if (transtest > d1)
+		r->rt = transdist;
+	else if (mirtest > d1)
+		r->rt = mirdist;
 				/* rayvalue() computes absorption */
 	return(1);
 }
@@ -212,13 +239,15 @@ register RAY  *r;
 
 #ifdef  DISPERSE
 
-static
-disperse(m, r, vt, tr, cet, abt)  /* check light sources for dispersion */
-OBJREC  *m;
-RAY  *r;
-FVECT  vt;
-double  tr;
-COLOR  cet, abt;
+static int
+disperse(  /* check light sources for dispersion */
+	OBJREC  *m,
+	RAY  *r,
+	FVECT  vt,
+	double  tr,
+	COLOR  cet,
+	COLOR  abt
+)
 {
 	RAY  sray, *entray;
 	FVECT  v1, v2, n1, n2;
@@ -349,9 +378,12 @@ COLOR  cet, abt;
 
 
 static int
-lambda(m, v2, dv, lr)			/* compute lambda for material */
-register OBJREC  *m;
-FVECT  v2, dv, lr;
+lambda(			/* compute lambda for material */
+	register OBJREC  *m,
+	FVECT  v2,
+	FVECT  dv,
+	FVECT  lr
+)
 {
 	FVECT  lrXdv, v2Xlr;
 	double  dtmp, denom;