--- ray/src/rt/normal.c	1991/05/08 08:27:48	1.9
+++ ray/src/rt/normal.c	1994/12/21 09:51:49	2.28
@@ -1,4 +1,4 @@
-/* Copyright (c) 1991 Regents of the University of California */
+/* Copyright (c) 1992 Regents of the University of California */
 
 #ifndef lint
 static char SCCSid[] = "$SunId$ LBL";
@@ -11,17 +11,25 @@ static char SCCSid[] = "$SunId$ LBL";
  *     12/19/85 - added stuff for metals.
  *     6/26/87 - improved specular model.
  *     9/28/87 - added model for translucent materials.
+ *     Later changes described in delta comments.
  */
 
 #include  "ray.h"
 
 #include  "otypes.h"
 
+#include  "random.h"
+
+extern double  specthresh;		/* specular sampling threshold */
+extern double  specjitter;		/* specular sampling jitter */
+
+extern int  backvis;			/* back faces visible? */
+
+static  gaussamp();
+
 /*
- *	This routine uses portions of the reflection
- *  model described by Cook and Torrance.
- *	The computation of specular components has been simplified by
- *  numerous approximations and ommisions to improve speed.
+ *	This routine implements the isotropic Gaussian
+ *  model described by Ward in Siggraph `92 article.
  *	We orient the surface towards the incoming ray, so a single
  *  surface can be used to represent an infinitely thin object.
  *
@@ -32,17 +40,23 @@ static char SCCSid[] = "$SunId$ LBL";
  *	red 	grn	blu	rspec	rough	trans	tspec
  */
 
-#define  BSPEC(m)	(6.0)		/* specularity parameter b */
+				/* specularity flags */
+#define  SP_REFL	01		/* has reflected specular component */
+#define  SP_TRAN	02		/* has transmitted specular */
+#define  SP_PURE	04		/* purely specular (zero roughness) */
+#define  SP_FLAT	010		/* flat reflecting surface */
+#define  SP_RBLT	020		/* reflection below sample threshold */
+#define  SP_TBLT	040		/* transmission below threshold */
 
-extern double  exp();
-
 typedef struct {
 	OBJREC  *mp;		/* material pointer */
-	RAY  *pr;		/* intersected ray */
+	RAY  *rp;		/* ray pointer */
+	short  specfl;		/* specularity flags, defined above */
 	COLOR  mcolor;		/* color of this material */
 	COLOR  scolor;		/* color of specular component */
 	FVECT  vrefl;		/* vector in direction of reflected ray */
-	double  alpha2;		/* roughness squared times 2 */
+	FVECT  prdir;		/* vector in transmitted direction */
+	double  alpha2;		/* roughness squared */
 	double  rdiff, rspec;	/* reflected specular, diffuse */
 	double  trans;		/* transmissivity */
 	double  tdiff, tspec;	/* transmitted specular, diffuse */
@@ -58,7 +72,8 @@ FVECT  ldir;			/* light source direction */
 double  omega;			/* light source size */
 {
 	double  ldot;
-	double  dtmp;
+	double  dtmp, d2;
+	FVECT  vtmp;
 	COLOR  ctmp;
 
 	setcolor(cval, 0.0, 0.0, 0.0);
@@ -79,19 +94,29 @@ double  omega;			/* light source size */
 		scalecolor(ctmp, dtmp);
 		addcolor(cval, ctmp);
 	}
-	if (ldot > FTINY && np->rspec > FTINY && np->alpha2 > FTINY) {
+	if (ldot > FTINY && (np->specfl&(SP_REFL|SP_PURE)) == SP_REFL) {
 		/*
 		 *  Compute specular reflection coefficient using
 		 *  gaussian distribution model.
 		 */
-						/* roughness + source */
-		dtmp = np->alpha2 + omega/(2.0*PI);
+						/* roughness */
+		dtmp = np->alpha2;
+						/* + source if flat */
+		if (np->specfl & SP_FLAT)
+			dtmp += omega/(4.0*PI);
+						/* half vector */
+		vtmp[0] = ldir[0] - np->rp->rdir[0];
+		vtmp[1] = ldir[1] - np->rp->rdir[1];
+		vtmp[2] = ldir[2] - np->rp->rdir[2];
+		d2 = DOT(vtmp, np->pnorm);
+		d2 *= d2;
+		d2 = (DOT(vtmp,vtmp) - d2) / d2;
 						/* gaussian */
-		dtmp = exp((DOT(np->vrefl,ldir)-1.)/dtmp)/(2.*PI)/dtmp;
+		dtmp = exp(-d2/dtmp)/(4.*PI*dtmp);
 						/* worth using? */
 		if (dtmp > FTINY) {
 			copycolor(ctmp, np->scolor);
-			dtmp *= omega;
+			dtmp *= omega * sqrt(ldot/np->pdot);
 			scalecolor(ctmp, dtmp);
 			addcolor(cval, ctmp);
 		}
@@ -105,78 +130,87 @@ double  omega;			/* light source size */
 		scalecolor(ctmp, dtmp);
 		addcolor(cval, ctmp);
 	}
-	if (ldot < -FTINY && np->tspec > FTINY && np->alpha2 > FTINY) {
+	if (ldot < -FTINY && (np->specfl&(SP_TRAN|SP_PURE)) == SP_TRAN) {
 		/*
 		 *  Compute specular transmission.  Specular transmission
-		 *  is unaffected by material color.
+		 *  is always modified by material color.
 		 */
 						/* roughness + source */
-		dtmp = np->alpha2 + omega/(2.0*PI);
+		dtmp = np->alpha2 + omega/PI;
 						/* gaussian */
-		dtmp = exp((DOT(np->pr->rdir,ldir)-1.)/dtmp)/(2.*PI)/dtmp;
+		dtmp = exp((2.*DOT(np->prdir,ldir)-2.)/dtmp)/(PI*dtmp);
 						/* worth using? */
 		if (dtmp > FTINY) {
-			dtmp *= np->tspec * omega;
-			setcolor(ctmp, dtmp, dtmp, dtmp);
+			copycolor(ctmp, np->mcolor);
+			dtmp *= np->tspec * omega * sqrt(-ldot/np->pdot);
+			scalecolor(ctmp, dtmp);
 			addcolor(cval, ctmp);
 		}
 	}
 }
 
 
-m_normal(m, r)			/* color a ray which hit something normal */
+m_normal(m, r)			/* color a ray that hit something normal */
 register OBJREC  *m;
 register RAY  *r;
 {
 	NORMDAT  nd;
 	double  transtest, transdist;
-	double  dtmp;
 	COLOR  ctmp;
 	register int  i;
-
-	if (m->oargs.nfargs != (m->otype == MAT_TRANS ? 7 : 5))
-		objerror(m, USER, "bad # arguments");
 						/* easy shadow test */
 	if (r->crtype & SHADOW && m->otype != MAT_TRANS)
-		return;
+		return(1);
+
+	if (m->oargs.nfargs != (m->otype == MAT_TRANS ? 7 : 5))
+		objerror(m, USER, "bad number of arguments");
 	nd.mp = m;
-	nd.pr = r;
+	nd.rp = r;
 						/* get material color */
 	setcolor(nd.mcolor, m->oargs.farg[0],
 			   m->oargs.farg[1],
 			   m->oargs.farg[2]);
 						/* get roughness */
+	nd.specfl = 0;
 	nd.alpha2 = m->oargs.farg[4];
-	nd.alpha2 *= 2.0 * nd.alpha2;
-						/* reorient if necessary */
-	if (r->rod < 0.0)
-		flipsurface(r);
+	if ((nd.alpha2 *= nd.alpha2) <= FTINY)
+		nd.specfl |= SP_PURE;
+						/* check for back side */
+	if (r->rod < 0.0) {
+		if (!backvis && m->otype != MAT_TRANS) {
+			raytrans(r);
+			return(1);
+		}
+		flipsurface(r);			/* reorient if backvis */
+	}
 						/* get modifiers */
 	raytexture(r, m->omod);
 	nd.pdot = raynormal(nd.pnorm, r);	/* perturb normal */
+	if (nd.pdot < .001)
+		nd.pdot = .001;			/* non-zero for dirnorm() */
 	multcolor(nd.mcolor, r->pcol);		/* modify material color */
-	r->rt = r->rot;				/* default ray length */
 	transtest = 0;
+	transdist = r->rot;
 						/* get specular component */
-	nd.rspec = m->oargs.farg[3];
-
-	if (nd.rspec > FTINY) {			/* has 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);
-						/* improved model */
-		dtmp = exp(-BSPEC(m)*nd.pdot);
-		for (i = 0; i < 3; i++)
-			colval(nd.scolor,i) += (1.0-colval(nd.scolor,i))*dtmp;
-		nd.rspec += (1.0-nd.rspec)*dtmp;
+						/* 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] + 2.0*nd.pdot*nd.pnorm[i];
+		if (DOT(nd.vrefl, r->ron) <= FTINY)	/* penetration? */
+			for (i = 0; i < 3; i++)		/* safety measure */
+				nd.vrefl[i] = r->rdir[i] + 2.*r->rod*r->ron[i];
 
-		if (nd.alpha2 <= FTINY && !(r->crtype & SHADOW)) {
+		if (!(r->crtype & SHADOW) && nd.specfl & SP_PURE) {
 			RAY  lr;
 			if (rayorigin(&lr, r, REFLECTED, nd.rspec) == 0) {
 				VCOPY(lr.rdir, nd.vrefl);
@@ -191,19 +225,32 @@ register RAY  *r;
 		nd.trans = m->oargs.farg[5]*(1.0 - nd.rspec);
 		nd.tspec = nd.trans * m->oargs.farg[6];
 		nd.tdiff = nd.trans - nd.tspec;
+		if (nd.tspec > FTINY) {
+			nd.specfl |= SP_TRAN;
+							/* check threshold */
+			if (!(nd.specfl & SP_PURE) &&
+					specthresh >= nd.tspec-FTINY)
+				nd.specfl |= SP_TBLT;
+			if (r->crtype & SHADOW ||
+					DOT(r->pert,r->pert) <= FTINY*FTINY) {
+				VCOPY(nd.prdir, r->rdir);
+				transtest = 2;
+			} else {
+				for (i = 0; i < 3; i++)		/* perturb */
+					nd.prdir[i] = r->rdir[i] - r->pert[i];
+				if (DOT(nd.prdir, r->ron) < -FTINY)
+					normalize(nd.prdir);	/* OK */
+				else
+					VCOPY(nd.prdir, r->rdir);
+			}
+		}
 	} else
 		nd.tdiff = nd.tspec = nd.trans = 0.0;
 						/* transmitted ray */
-	if (nd.tspec > FTINY && nd.alpha2 <= FTINY) {
+	if ((nd.specfl&(SP_TRAN|SP_PURE)) == (SP_TRAN|SP_PURE)) {
 		RAY  lr;
 		if (rayorigin(&lr, r, TRANS, nd.tspec) == 0) {
-			if (DOT(r->pert,r->pert) > FTINY*FTINY) {
-				for (i = 0; i < 3; i++)	/* perturb direction */
-					lr.rdir[i] = r->rdir[i] -
-							.75*r->pert[i];
-				normalize(lr.rdir);
-			} else
-				transtest = 2;
+			VCOPY(lr.rdir, nd.prdir);
 			rayvalue(&lr);
 			scalecolor(lr.rcol, nd.tspec);
 			multcolor(lr.rcol, nd.mcolor);	/* modified by color */
@@ -211,32 +258,41 @@ register RAY  *r;
 			transtest *= bright(lr.rcol);
 			transdist = r->rot + lr.rt;
 		}
-	}
+	} else
+		transtest = 0;
+
 	if (r->crtype & SHADOW)			/* the rest is shadow */
-		return;
+		return(1);
 						/* diffuse reflection */
 	nd.rdiff = 1.0 - nd.trans - nd.rspec;
 
-	if (nd.rdiff <= FTINY && nd.tdiff <= FTINY && nd.alpha2 <= FTINY)
-		return;				/* purely specular */
+	if (nd.specfl & SP_PURE && nd.rdiff <= FTINY && nd.tdiff <= FTINY)
+		return(1);			/* 100% pure specular */
 
+	if (r->ro != NULL && (r->ro->otype == OBJ_FACE ||
+			r->ro->otype == OBJ_RING))
+		nd.specfl |= SP_FLAT;
+
+	if (nd.specfl & (SP_REFL|SP_TRAN) && !(nd.specfl & SP_PURE))
+		gaussamp(r, &nd);
+
 	if (nd.rdiff > FTINY) {		/* ambient from this side */
 		ambient(ctmp, r);
-		if (nd.alpha2 <= FTINY)
-			scalecolor(ctmp, nd.rdiff);
-		else
+		if (nd.specfl & SP_RBLT)
 			scalecolor(ctmp, 1.0-nd.trans);
+		else
+			scalecolor(ctmp, nd.rdiff);
 		multcolor(ctmp, nd.mcolor);	/* modified by material color */
 		addcolor(r->rcol, ctmp);	/* add to returned color */
 	}
 	if (nd.tdiff > FTINY) {		/* ambient from other side */
 		flipsurface(r);
 		ambient(ctmp, r);
-		if (nd.alpha2 <= FTINY)
-			scalecolor(ctmp, nd.tdiff);
-		else
+		if (nd.specfl & SP_TBLT)
 			scalecolor(ctmp, nd.trans);
-		multcolor(ctmp, nd.mcolor);
+		else
+			scalecolor(ctmp, nd.tdiff);
+		multcolor(ctmp, nd.mcolor);	/* modified by color */
 		addcolor(r->rcol, ctmp);
 		flipsurface(r);
 	}
@@ -245,4 +301,84 @@ register RAY  *r;
 					/* check distance */
 	if (transtest > bright(r->rcol))
 		r->rt = transdist;
+
+	return(1);
+}
+
+
+static
+gaussamp(r, np)			/* sample gaussian specular */
+RAY  *r;
+register NORMDAT  *np;
+{
+	RAY  sr;
+	FVECT  u, v, h;
+	double  rv[2];
+	double  d, sinp, cosp;
+	register int  i;
+					/* quick test */
+	if ((np->specfl & (SP_REFL|SP_RBLT)) != SP_REFL &&
+			(np->specfl & (SP_TRAN|SP_TBLT)) != SP_TRAN)
+		return;
+					/* set up sample coordinates */
+	v[0] = v[1] = v[2] = 0.0;
+	for (i = 0; i < 3; i++)
+		if (np->pnorm[i] < 0.6 && np->pnorm[i] > -0.6)
+			break;
+	v[i] = 1.0;
+	fcross(u, v, np->pnorm);
+	normalize(u);
+	fcross(v, np->pnorm, u);
+					/* compute reflection */
+	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);
+		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);
+		ndims--;
+	}
 }