--- ray/src/rt/normal.c	1995/09/15 15:47:30	2.29
+++ ray/src/rt/normal.c	2003/06/17 21:49:57	2.44
@@ -1,9 +1,6 @@
-/* Copyright (c) 1992 Regents of the University of California */
-
 #ifndef lint
-static char SCCSid[] = "$SunId$ LBL";
+static const char RCSid[] = "$Id: normal.c,v 2.44 2003/06/17 21:49:57 greg Exp $";
 #endif
-
 /*
  *  normal.c - shading function for normal materials.
  *
@@ -14,19 +11,22 @@ static char SCCSid[] = "$SunId$ LBL";
  *     Later changes described in delta comments.
  */
 
+#include "copyright.h"
+
 #include  "ray.h"
 
 #include  "otypes.h"
 
 #include  "random.h"
 
-extern double  specthresh;		/* specular sampling threshold */
-extern double  specjitter;		/* specular sampling jitter */
+#ifndef  MAXITER
+#define  MAXITER	10		/* maximum # specular ray attempts */
+#endif
+					/* estimate of Fresnel function */
+#define  FRESNE(ci)	(exp(-5.85*(ci)) - 0.00287989916)
 
-extern int  backvis;			/* back faces visible? */
+static void  gaussamp();
 
-static  gaussamp();
-
 /*
  *	This routine implements the isotropic Gaussian
  *  model described by Ward in Siggraph `92 article.
@@ -65,6 +65,7 @@ typedef struct {
 }  NORMDAT;		/* normal material data */
 
 
+static void
 dirnorm(cval, np, ldir, omega)		/* compute source contribution */
 COLOR  cval;			/* returned coefficient */
 register NORMDAT  *np;		/* material data */
@@ -72,6 +73,7 @@ FVECT  ldir;			/* light source direction */
 double  omega;			/* light source size */
 {
 	double  ldot;
+	double  ldiff;
 	double  dtmp, d2;
 	FVECT  vtmp;
 	COLOR  ctmp;
@@ -83,14 +85,19 @@ double  omega;			/* light source size */
 	if (ldot < 0.0 ? np->trans <= FTINY : np->trans >= 1.0-FTINY)
 		return;		/* wrong side */
 
-	if (ldot > FTINY && np->rdiff > FTINY) {
+				/* Fresnel estimate */
+	ldiff = np->rdiff;
+	if (np->specfl & SP_PURE && (np->rspec > FTINY & ldiff > FTINY))
+		ldiff *= 1. - FRESNE(fabs(ldot));
+
+	if (ldot > FTINY && ldiff > FTINY) {
 		/*
 		 *  Compute and add diffuse reflected component to returned
 		 *  color.  The diffuse reflected component will always be
 		 *  modified by the color of the material.
 		 */
 		copycolor(ctmp, np->mcolor);
-		dtmp = ldot * omega * np->rdiff / PI;
+		dtmp = ldot * omega * ldiff / PI;
 		scalecolor(ctmp, dtmp);
 		addcolor(cval, ctmp);
 	}
@@ -150,11 +157,13 @@ double  omega;			/* light source size */
 }
 
 
+int
 m_normal(m, r)			/* color a ray that hit something normal */
 register OBJREC  *m;
 register RAY  *r;
 {
 	NORMDAT  nd;
+	double  fest;
 	double  transtest, transdist;
 	double	mirtest, mirdist;
 	int	hastexture;
@@ -173,8 +182,10 @@ register RAY  *r;
 			raytrans(r);
 			return(1);
 		}
+		raytexture(r, m->omod);
 		flipsurface(r);			/* reorient if backvis */
-	}
+	} else
+		raytexture(r, m->omod);
 	nd.mp = m;
 	nd.rp = r;
 						/* get material color */
@@ -186,55 +197,27 @@ register RAY  *r;
 	nd.alpha2 = m->oargs.farg[4];
 	if ((nd.alpha2 *= nd.alpha2) <= FTINY)
 		nd.specfl |= SP_PURE;
-	if (r->ro != NULL && isflat(r->ro->otype))
-		nd.specfl |= SP_FLAT;
-						/* get modifiers */
-	raytexture(r, m->omod);
-	if (hastexture = DOT(r->pert,r->pert) > FTINY*FTINY)
+
+	if (hastexture = (DOT(r->pert,r->pert) > FTINY*FTINY)) {
 		nd.pdot = raynormal(nd.pnorm, r);	/* perturb normal */
-	else {
+	} else {
 		VCOPY(nd.pnorm, r->ron);
 		nd.pdot = r->rod;
 	}
+	if (r->ro != NULL && isflat(r->ro->otype))
+		nd.specfl |= SP_FLAT;
 	if (nd.pdot < .001)
 		nd.pdot = .001;			/* non-zero for dirnorm() */
 	multcolor(nd.mcolor, r->pcol);		/* modify material color */
 	mirtest = transtest = 0;
 	mirdist = transdist = r->rot;
-						/* get specular component */
-	if ((nd.rspec = m->oargs.farg[3]) > FTINY) {
-		nd.specfl |= SP_REFL;
-						/* compute specular color */
-		if (m->otype == MAT_METAL)
-			copycolor(nd.scolor, nd.mcolor);
-		else
-			setcolor(nd.scolor, 1.0, 1.0, 1.0);
-		scalecolor(nd.scolor, nd.rspec);
-						/* check threshold */
-		if (!(nd.specfl & SP_PURE) && specthresh >= nd.rspec-FTINY)
-			nd.specfl |= SP_RBLT;
-						/* compute reflected ray */
-		for (i = 0; i < 3; i++)
-			nd.vrefl[i] = r->rdir[i] + 2.*nd.pdot*nd.pnorm[i];
-						/* penetration? */
-		if (hastexture && DOT(nd.vrefl, r->ron) <= FTINY)
-			for (i = 0; i < 3; i++)		/* safety measure */
-				nd.vrefl[i] = r->rdir[i] + 2.*r->rod*r->ron[i];
-
-		if (!(r->crtype & SHADOW) && nd.specfl & SP_PURE) {
-			RAY  lr;
-			if (rayorigin(&lr, r, REFLECTED, nd.rspec) == 0) {
-				VCOPY(lr.rdir, nd.vrefl);
-				rayvalue(&lr);
-				multcolor(lr.rcol, nd.scolor);
-				addcolor(r->rcol, lr.rcol);
-				if (!hastexture && nd.specfl & SP_FLAT) {
-					mirtest = 2.*bright(lr.rcol);
-					mirdist = r->rot + lr.rt;
-				}
-			}
-		}
-	}
+	nd.rspec = m->oargs.farg[3];
+						/* compute Fresnel approx. */
+	if (nd.specfl & SP_PURE && nd.rspec > FTINY) {
+		fest = FRESNE(r->rod);
+		nd.rspec += fest*(1. - nd.rspec);
+	} else
+		fest = 0.;
 						/* compute transmission */
 	if (m->otype == MAT_TRANS) {
 		nd.trans = m->oargs.farg[5]*(1.0 - nd.rspec);
@@ -261,7 +244,7 @@ register RAY  *r;
 	} else
 		nd.tdiff = nd.tspec = nd.trans = 0.0;
 						/* transmitted ray */
-	if ((nd.specfl&(SP_TRAN|SP_PURE)) == (SP_TRAN|SP_PURE)) {
+	if ((nd.specfl&(SP_TRAN|SP_PURE|SP_TBLT)) == (SP_TRAN|SP_PURE)) {
 		RAY  lr;
 		if (rayorigin(&lr, r, TRANS, nd.tspec) == 0) {
 			VCOPY(lr.rdir, nd.prdir);
@@ -279,17 +262,56 @@ register RAY  *r;
 		r->rt = transdist;
 		return(1);
 	}
+						/* get specular reflection */
+	if (nd.rspec > FTINY) {
+		nd.specfl |= SP_REFL;
+						/* compute specular color */
+		if (m->otype != MAT_METAL) {
+			setcolor(nd.scolor, nd.rspec, nd.rspec, nd.rspec);
+		} else if (fest > FTINY) {
+			d = nd.rspec*(1. - fest);
+			for (i = 0; i < 3; i++)
+				nd.scolor[i] = fest + nd.mcolor[i]*d;
+		} else {
+			copycolor(nd.scolor, nd.mcolor);
+			scalecolor(nd.scolor, nd.rspec);
+		}
+						/* check threshold */
+		if (!(nd.specfl & SP_PURE) && specthresh >= nd.rspec-FTINY)
+			nd.specfl |= SP_RBLT;
+						/* compute reflected ray */
+		for (i = 0; i < 3; i++)
+			nd.vrefl[i] = r->rdir[i] + 2.*nd.pdot*nd.pnorm[i];
+						/* penetration? */
+		if (hastexture && DOT(nd.vrefl, r->ron) <= FTINY)
+			for (i = 0; i < 3; i++)		/* safety measure */
+				nd.vrefl[i] = r->rdir[i] + 2.*r->rod*r->ron[i];
+	}
+						/* reflected ray */
+	if ((nd.specfl&(SP_REFL|SP_PURE|SP_RBLT)) == (SP_REFL|SP_PURE)) {
+		RAY  lr;
+		if (rayorigin(&lr, r, REFLECTED, nd.rspec) == 0) {
+			VCOPY(lr.rdir, nd.vrefl);
+			rayvalue(&lr);
+			multcolor(lr.rcol, nd.scolor);
+			addcolor(r->rcol, lr.rcol);
+			if (!hastexture && nd.specfl & SP_FLAT) {
+				mirtest = 2.*bright(lr.rcol);
+				mirdist = r->rot + lr.rt;
+			}
+		}
+	}
 						/* diffuse reflection */
 	nd.rdiff = 1.0 - nd.trans - nd.rspec;
 
 	if (nd.specfl & SP_PURE && nd.rdiff <= FTINY && nd.tdiff <= FTINY)
 		return(1);			/* 100% pure specular */
 
-	if (nd.specfl & (SP_REFL|SP_TRAN) && !(nd.specfl & SP_PURE))
-		gaussamp(r, &nd);
+	if (!(nd.specfl & SP_PURE))
+		gaussamp(r, &nd);		/* checks *BLT flags */
 
 	if (nd.rdiff > FTINY) {		/* ambient from this side */
-		ambient(ctmp, r);
+		ambient(ctmp, r, hastexture?nd.pnorm:r->ron);
 		if (nd.specfl & SP_RBLT)
 			scalecolor(ctmp, 1.0-nd.trans);
 		else
@@ -299,7 +321,14 @@ register RAY  *r;
 	}
 	if (nd.tdiff > FTINY) {		/* ambient from other side */
 		flipsurface(r);
-		ambient(ctmp, r);
+		if (hastexture) {
+			FVECT  bnorm;
+			bnorm[0] = -nd.pnorm[0];
+			bnorm[1] = -nd.pnorm[1];
+			bnorm[2] = -nd.pnorm[2];
+			ambient(ctmp, r, bnorm);
+		} else
+			ambient(ctmp, r, r->ron);
 		if (nd.specfl & SP_TBLT)
 			scalecolor(ctmp, nd.trans);
 		else
@@ -321,7 +350,7 @@ register RAY  *r;
 }
 
 
-static
+static void
 gaussamp(r, np)			/* sample gaussian specular */
 RAY  *r;
 register NORMDAT  *np;
@@ -330,6 +359,7 @@ register NORMDAT  *np;
 	FVECT  u, v, h;
 	double  rv[2];
 	double  d, sinp, cosp;
+	int  niter;
 	register int  i;
 					/* quick test */
 	if ((np->specfl & (SP_REFL|SP_RBLT)) != SP_REFL &&
@@ -348,52 +378,63 @@ register NORMDAT  *np;
 	if ((np->specfl & (SP_REFL|SP_RBLT)) == SP_REFL &&
 			rayorigin(&sr, r, SPECULAR, np->rspec) == 0) {
 		dimlist[ndims++] = (int)np->mp;
-		d = urand(ilhash(dimlist,ndims)+samplendx);
-		multisamp(rv, 2, d);
-		d = 2.0*PI * rv[0];
-		cosp = cos(d);
-		sinp = sin(d);
-		rv[1] = 1.0 - specjitter*rv[1];
-		if (rv[1] <= FTINY)
-			d = 1.0;
-		else
-			d = sqrt( np->alpha2 * -log(rv[1]) );
-		for (i = 0; i < 3; i++)
-			h[i] = np->pnorm[i] + d*(cosp*u[i] + sinp*v[i]);
-		d = -2.0 * DOT(h, r->rdir) / (1.0 + d*d);
-		for (i = 0; i < 3; i++)
-			sr.rdir[i] = r->rdir[i] + d*h[i];
-		if (DOT(sr.rdir, r->ron) <= FTINY)
-			VCOPY(sr.rdir, np->vrefl);	/* jitter no good */
-		rayvalue(&sr);
-		multcolor(sr.rcol, np->scolor);
-		addcolor(r->rcol, sr.rcol);
+		for (niter = 0; niter < MAXITER; niter++) {
+			if (niter)
+				d = frandom();
+			else
+				d = urand(ilhash(dimlist,ndims)+samplendx);
+			multisamp(rv, 2, d);
+			d = 2.0*PI * rv[0];
+			cosp = tcos(d);
+			sinp = tsin(d);
+			rv[1] = 1.0 - specjitter*rv[1];
+			if (rv[1] <= FTINY)
+				d = 1.0;
+			else
+				d = sqrt( np->alpha2 * -log(rv[1]) );
+			for (i = 0; i < 3; i++)
+				h[i] = np->pnorm[i] + d*(cosp*u[i] + sinp*v[i]);
+			d = -2.0 * DOT(h, r->rdir) / (1.0 + d*d);
+			for (i = 0; i < 3; i++)
+				sr.rdir[i] = r->rdir[i] + d*h[i];
+			if (DOT(sr.rdir, r->ron) > FTINY) {
+				rayvalue(&sr);
+				multcolor(sr.rcol, np->scolor);
+				addcolor(r->rcol, sr.rcol);
+				break;
+			}
+		}
 		ndims--;
 	}
 					/* compute transmission */
 	if ((np->specfl & (SP_TRAN|SP_TBLT)) == SP_TRAN &&
 			rayorigin(&sr, r, SPECULAR, np->tspec) == 0) {
 		dimlist[ndims++] = (int)np->mp;
-		d = urand(ilhash(dimlist,ndims)+1823+samplendx);
-		multisamp(rv, 2, d);
-		d = 2.0*PI * rv[0];
-		cosp = cos(d);
-		sinp = sin(d);
-		rv[1] = 1.0 - specjitter*rv[1];
-		if (rv[1] <= FTINY)
-			d = 1.0;
-		else
-			d = sqrt( -log(rv[1]) * np->alpha2 );
-		for (i = 0; i < 3; i++)
-			sr.rdir[i] = np->prdir[i] + d*(cosp*u[i] + sinp*v[i]);
-		if (DOT(sr.rdir, r->ron) < -FTINY)
-			normalize(sr.rdir);		/* OK, normalize */
-		else
-			VCOPY(sr.rdir, np->prdir);	/* else no jitter */
-		rayvalue(&sr);
-		scalecolor(sr.rcol, np->tspec);
-		multcolor(sr.rcol, np->mcolor);		/* modified by color */
-		addcolor(r->rcol, sr.rcol);
+		for (niter = 0; niter < MAXITER; niter++) {
+			if (niter)
+				d = frandom();
+			else
+				d = urand(ilhash(dimlist,ndims)+1823+samplendx);
+			multisamp(rv, 2, d);
+			d = 2.0*PI * rv[0];
+			cosp = tcos(d);
+			sinp = tsin(d);
+			rv[1] = 1.0 - specjitter*rv[1];
+			if (rv[1] <= FTINY)
+				d = 1.0;
+			else
+				d = sqrt( np->alpha2 * -log(rv[1]) );
+			for (i = 0; i < 3; i++)
+				sr.rdir[i] = np->prdir[i] + d*(cosp*u[i] + sinp*v[i]);
+			if (DOT(sr.rdir, r->ron) < -FTINY) {
+				normalize(sr.rdir);	/* OK, normalize */
+				rayvalue(&sr);
+				scalecolor(sr.rcol, np->tspec);
+				multcolor(sr.rcol, np->mcolor);	/* modified */
+				addcolor(r->rcol, sr.rcol);
+				break;
+			}
+		}
 		ndims--;
 	}
 }