text: #ifndef lint
  static const char	RCSid[] = "$Id: m_brdf.c,v 2.29 2013/03/20 23:07:51 greg Exp $";
  #endif
  /*
   *  Shading for materials with arbitrary BRDF's
   */
  
  #include "copyright.h"
  
  #include  "ray.h"
  #include  "ambient.h"
  #include  "data.h"
  #include  "source.h"
  #include  "otypes.h"
  #include  "rtotypes.h"
  #include  "func.h"
  
  /*
   *	Arguments to this material include the color and specularity.
   *  String arguments include the reflection function and files.
   *  The BRDF is currently used just for the specular component to light
   *  sources.  Reflectance values or data coordinates are functions
   *  of the direction to the light source.  (Data modification functions
   *  are passed the source direction as args 2-4.)
   *	We orient the surface towards the incoming ray, so a single
   *  surface can be used to represent an infinitely thin object.
   *
   *  Arguments for MAT_PFUNC and MAT_MFUNC are:
   *	2+	func	funcfile	transform
   *	0
   *	4+	red	grn	blu	specularity	A5 ..
   *
   *  Arguments for MAT_PDATA and MAT_MDATA are:
   *	4+	func	datafile	funcfile	v0 ..	transform
   *	0
   *	4+	red	grn	blu	specularity	A5 ..
   *
   *  Arguments for MAT_TFUNC are:
   *	2+	func	funcfile	transform
   *	0
   *	6+	red	grn	blu	rspec	trans	tspec	A7 ..
   *
   *  Arguments for MAT_TDATA are:
   *	4+	func	datafile	funcfile	v0 ..	transform
   *	0
   *	6+	red	grn	blu	rspec	trans	tspec	A7 ..
   *
   *  Arguments for the more general MAT_BRTDF are:
   *	10+	rrefl	grefl	brefl
   *		rtrns	gtrns	btrns
   *		rbrtd	gbrtd	bbrtd
   *		funcfile	transform
   *	0
   *	9+	rdf	gdf	bdf
   *		rdb	gdb	bdb
   *		rdt	gdt	bdt	A10 ..
   *
   *	In addition to the normal variables available to functions,
   *  we define the following:
   *		NxP, NyP, NzP -		perturbed surface normal
   *		RdotP -			perturbed ray dot product
   *		CrP, CgP, CbP -		perturbed material color (or pattern)
   */
  
  typedef struct {
  	OBJREC  *mp;		/* material pointer */
  	RAY  *pr;		/* intersected ray */
  	DATARRAY  *dp;		/* data array for PDATA, MDATA or TDATA */
  	COLOR  mcolor;		/* material (or pattern) color */
  	COLOR  rdiff;		/* diffuse reflection */
  	COLOR  tdiff;		/* diffuse transmission */
  	double  rspec;		/* specular reflectance (1 for BRDTF) */
  	double  trans;		/* transmissivity (.5 for BRDTF) */
  	double  tspec;		/* specular transmittance (1 for BRDTF) */
  	FVECT  pnorm;		/* perturbed surface normal */
  	double  pdot;		/* perturbed dot product */
  }  BRDFDAT;		/* BRDF material data */
  
  
  static int setbrdfunc(BRDFDAT *np);
  
  
  static void
  dirbrdf(		/* compute source contribution */
  	COLOR  cval,			/* returned coefficient */
  	void  *nnp,		/* material data */
  	FVECT  ldir,			/* light source direction */
  	double  omega			/* light source size */
  )
  {
  	BRDFDAT *np = nnp;
  	double  ldot;
  	double  dtmp;
  	COLOR  ctmp;
  	FVECT  ldx;
  	static double  vldx[5], pt[MAXDIM];
  	char	**sa;
  	int	i;
  #define lddx (vldx+1)
  
  	setcolor(cval, 0.0, 0.0, 0.0);
  	
  	ldot = DOT(np->pnorm, ldir);
  
  	if (ldot <= FTINY && ldot >= -FTINY)
  		return;		/* too close to grazing */
  
  	if (ldot < 0.0 ? np->trans <= FTINY : np->trans >= 1.0-FTINY)
  		return;		/* wrong side */
  
  	if (ldot > 0.0) {
  		/*
  		 *  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->rdiff);
  		dtmp = ldot * omega / PI;
  		scalecolor(ctmp, dtmp);
  		addcolor(cval, ctmp);
  	} else {
  		/*
  		 *  Diffuse transmitted component.
  		 */
  		copycolor(ctmp, np->tdiff);
  		dtmp = -ldot * omega / PI;
  		scalecolor(ctmp, dtmp);
  		addcolor(cval, ctmp);
  	}
  	if (ldot > 0.0 ? np->rspec <= FTINY : np->tspec <= FTINY)
  		return;		/* diffuse only */
  					/* set up function */
  	setbrdfunc(np);
  	sa = np->mp->oargs.sarg;
  	errno = 0;
  					/* transform light vector */
  	multv3(ldx, ldir, funcxf.xfm);
  	for (i = 0; i < 3; i++)
  		lddx[i] = ldx[i]/funcxf.sca;
  	lddx[3] = omega;
  					/* compute BRTDF */
  	if (np->mp->otype == MAT_BRTDF) {
  		if (sa[6][0] == '0')		/* special case */
  			colval(ctmp,RED) = 0.0;
  		else
  			colval(ctmp,RED) = funvalue(sa[6], 4, lddx);
  		if (sa[7][0] == '0')
  			colval(ctmp,GRN) = 0.0;
  		else if (!strcmp(sa[7],sa[6]))
  			colval(ctmp,GRN) = colval(ctmp,RED);
  		else
  			colval(ctmp,GRN) = funvalue(sa[7], 4, lddx);
  		if (!strcmp(sa[8],sa[6]))
  			colval(ctmp,BLU) = colval(ctmp,RED);
  		else if (!strcmp(sa[8],sa[7]))
  			colval(ctmp,BLU) = colval(ctmp,GRN);
  		else
  			colval(ctmp,BLU) = funvalue(sa[8], 4, lddx);
  		dtmp = bright(ctmp);
  	} else if (np->dp == NULL) {
  		dtmp = funvalue(sa[0], 4, lddx);
  		setcolor(ctmp, dtmp, dtmp, dtmp);
  	} else {
  		for (i = 0; i < np->dp->nd; i++)
  			pt[i] = funvalue(sa[3+i], 4, lddx);
  		vldx[0] = datavalue(np->dp, pt);
  		dtmp = funvalue(sa[0], 5, vldx);
  		setcolor(ctmp, dtmp, dtmp, dtmp);
  	}
  	if ((errno == EDOM) | (errno == ERANGE)) {
  		objerror(np->mp, WARNING, "compute error");
  		return;
  	}
  	if (dtmp <= FTINY)
  		return;
  	if (ldot > 0.0) {
  		/*
  		 *  Compute reflected non-diffuse component.
  		 */
  		if ((np->mp->otype == MAT_MFUNC) | (np->mp->otype == MAT_MDATA))
  			multcolor(ctmp, np->mcolor);
  		dtmp = ldot * omega * np->rspec;
  		scalecolor(ctmp, dtmp);
  		addcolor(cval, ctmp);
  	} else {
  		/*
  		 *  Compute transmitted non-diffuse component.
  		 */
  		if ((np->mp->otype == MAT_TFUNC) | (np->mp->otype == MAT_TDATA))
  			multcolor(ctmp, np->mcolor);
  		dtmp = -ldot * omega * np->tspec;
  		scalecolor(ctmp, dtmp);
  		addcolor(cval, ctmp);
  	}
  #undef lddx
  }
  
  
  int
  m_brdf(			/* color a ray that hit a BRDTfunc material */
  	OBJREC  *m,
  	RAY  *r
  )
  {
  	int  hitfront = 1;
  	BRDFDAT  nd;
  	RAY  sr;
  	double  mirtest=0, mirdist=0;
  	double  transtest, transdist;
  	int  hasrefl, hastrans;
  	int  hastexture;
  	COLOR  ctmp;
  	FVECT  vtmp;
  	double  d;
  	MFUNC  *mf;
  	int  i;
  						/* check arguments */
  	if ((m->oargs.nsargs < 10) | (m->oargs.nfargs < 9))
  		objerror(m, USER, "bad # arguments");
  	nd.mp = m;
  	nd.pr = r;
  						/* dummy values */
  	nd.rspec = nd.tspec = 1.0;
  	nd.trans = 0.5;
  						/* diffuse reflectance */
  	if (r->rod > 0.0)
  		setcolor(nd.rdiff, m->oargs.farg[0],
  				m->oargs.farg[1],
  				m->oargs.farg[2]);
  	else
  		setcolor(nd.rdiff, m->oargs.farg[3],
  				m->oargs.farg[4],
  				m->oargs.farg[5]);
  						/* diffuse transmittance */
  	setcolor(nd.tdiff, m->oargs.farg[6],
  			m->oargs.farg[7],
  			m->oargs.farg[8]);
  						/* get modifiers */
  	raytexture(r, m->omod);
  	hastexture = DOT(r->pert,r->pert) > FTINY*FTINY;
  	if (hastexture) {			/* perturb normal */
  		nd.pdot = raynormal(nd.pnorm, r);
  	} else {
  		VCOPY(nd.pnorm, r->ron);
  		nd.pdot = r->rod;
  	}
  	if (r->rod < 0.0) {			/* orient perturbed values */
  		nd.pdot = -nd.pdot;
  		for (i = 0; i < 3; i++) {
  			nd.pnorm[i] = -nd.pnorm[i];
  			r->pert[i] = -r->pert[i];
  		}
  		hitfront = 0;
  	}
  	copycolor(nd.mcolor, r->pcol);		/* get pattern color */
  	multcolor(nd.rdiff, nd.mcolor);		/* modify diffuse values */
  	multcolor(nd.tdiff, nd.mcolor);
  	hasrefl = bright(nd.rdiff) > FTINY;
  	hastrans = bright(nd.tdiff) > FTINY;
  						/* load cal file */
  	nd.dp = NULL;
  	mf = getfunc(m, 9, 0x3f, 0);
  						/* compute transmitted ray */
  	setbrdfunc(&nd);
  	errno = 0;
  	setcolor(ctmp, evalue(mf->ep[3]),
  			evalue(mf->ep[4]),
  			evalue(mf->ep[5]));
  	if ((errno == EDOM) | (errno == ERANGE))
  		objerror(m, WARNING, "compute error");
  	else if (rayorigin(&sr, TRANS, r, ctmp) == 0) {
  		if (!(r->crtype & SHADOW) && hastexture) {
  						/* perturb direction */
  			VSUM(sr.rdir, r->rdir, r->pert, -.75);
  			if (normalize(sr.rdir) == 0.0) {
  				objerror(m, WARNING, "illegal perturbation");
  				VCOPY(sr.rdir, r->rdir);
  			}
  		} else {
  			VCOPY(sr.rdir, r->rdir);
  		}
  		rayvalue(&sr);
  		multcolor(sr.rcol, sr.rcoef);
  		addcolor(r->rcol, sr.rcol);
  		if (!hastexture) {
  			transtest = 2.0*bright(sr.rcol);
  			transdist = r->rot + sr.rt;
  		}
  	}
  	if (r->crtype & SHADOW)			/* the rest is shadow */
  		return(1);
  						/* compute reflected ray */
  	setbrdfunc(&nd);
  	errno = 0;
  	setcolor(ctmp, evalue(mf->ep[0]),
  			evalue(mf->ep[1]),
  			evalue(mf->ep[2]));
  	if ((errno == EDOM) | (errno == ERANGE))
  		objerror(m, WARNING, "compute error");
  	else if (rayorigin(&sr, REFLECTED, r, ctmp) == 0) {
  		VSUM(sr.rdir, r->rdir, nd.pnorm, 2.*nd.pdot);
  		checknorm(sr.rdir);
  		rayvalue(&sr);
  		multcolor(sr.rcol, sr.rcoef);
  		addcolor(r->rcol, sr.rcol);
  		if (!hastexture && r->ro != NULL && isflat(r->ro->otype)) {
  			mirtest = 2.0*bright(sr.rcol);
  			mirdist = r->rot + sr.rt;
  		}
  	}
  						/* compute ambient */
  	if (hasrefl) {
  		if (!hitfront)
  			flipsurface(r);
  		copycolor(ctmp, nd.rdiff);
  		multambient(ctmp, r, nd.pnorm);
  		addcolor(r->rcol, ctmp);	/* add to returned color */
  		if (!hitfront)
  			flipsurface(r);
  	}
  	if (hastrans) {				/* from other side */
  		if (hitfront)
  			flipsurface(r);
  		vtmp[0] = -nd.pnorm[0];
  		vtmp[1] = -nd.pnorm[1];
  		vtmp[2] = -nd.pnorm[2];
  		copycolor(ctmp, nd.tdiff);
  		multambient(ctmp, r, vtmp);
  		addcolor(r->rcol, ctmp);
  		if (hitfront)
  			flipsurface(r);
  	}
  	if (hasrefl | hastrans || m->oargs.sarg[6][0] != '0')
  		direct(r, dirbrdf, &nd);	/* add direct component */
  
  	d = bright(r->rcol);			/* set effective distance */
  	if (transtest > d)
  		r->rt = transdist;
  	else if (mirtest > d)
  		r->rt = mirdist;
  
  	return(1);
  }
  
  
  
  int
  m_brdf2(			/* color a ray that hit a BRDF material */
  	OBJREC  *m,
  	RAY  *r
  )
  {
  	BRDFDAT  nd;
  	COLOR  ctmp;
  	FVECT  vtmp;
  	double  dtmp;
  						/* always a shadow */
  	if (r->crtype & SHADOW)
  		return(1);
  						/* check arguments */
  	if ((m->oargs.nsargs < (hasdata(m->otype)?4:2)) | (m->oargs.nfargs <
  			((m->otype==MAT_TFUNC)|(m->otype==MAT_TDATA)?6:4)))
  		objerror(m, USER, "bad # arguments");
  						/* check for back side */
  	if (r->rod < 0.0) {
  		if (!backvis && m->otype != MAT_TFUNC
  				&& m->otype != MAT_TDATA) {
  			raytrans(r);
  			return(1);
  		}
  		raytexture(r, m->omod);
  		flipsurface(r);			/* reorient if backvis */
  	} else
  		raytexture(r, m->omod);
  
  	nd.mp = m;
  	nd.pr = r;
  						/* get material color */
  	setcolor(nd.mcolor, m->oargs.farg[0],
  			m->oargs.farg[1],
  			m->oargs.farg[2]);
  						/* get specular component */
  	nd.rspec = m->oargs.farg[3];
  						/* compute transmittance */
  	if ((m->otype == MAT_TFUNC) | (m->otype == MAT_TDATA)) {
  		nd.trans = m->oargs.farg[4]*(1.0 - nd.rspec);
  		nd.tspec = nd.trans * m->oargs.farg[5];
  		dtmp = nd.trans - nd.tspec;
  		setcolor(nd.tdiff, dtmp, dtmp, dtmp);
  	} else {
  		nd.tspec = nd.trans = 0.0;
  		setcolor(nd.tdiff, 0.0, 0.0, 0.0);
  	}
  						/* compute reflectance */
  	dtmp = 1.0 - nd.trans - nd.rspec;
  	setcolor(nd.rdiff, dtmp, dtmp, dtmp);
  	nd.pdot = raynormal(nd.pnorm, r);	/* perturb normal */
  	multcolor(nd.mcolor, r->pcol);		/* modify material color */
  	multcolor(nd.rdiff, nd.mcolor);
  	multcolor(nd.tdiff, nd.mcolor);
  						/* load auxiliary files */
  	if (hasdata(m->otype)) {
  		nd.dp = getdata(m->oargs.sarg[1]);
  		getfunc(m, 2, 0, 0);
  	} else {
  		nd.dp = NULL;
  		getfunc(m, 1, 0, 0);
  	}
  						/* compute ambient */
  	if (nd.trans < 1.0-FTINY) {
  		copycolor(ctmp, nd.mcolor);	/* modified by material color */
  		scalecolor(ctmp, 1.0-nd.trans);
  		multambient(ctmp, r, nd.pnorm);
  		addcolor(r->rcol, ctmp);	/* add to returned color */
  	}
  	if (nd.trans > FTINY) {		/* from other side */
  		flipsurface(r);
  		vtmp[0] = -nd.pnorm[0];
  		vtmp[1] = -nd.pnorm[1];
  		vtmp[2] = -nd.pnorm[2];
  		copycolor(ctmp, nd.mcolor);
  		scalecolor(ctmp, nd.trans);
  		multambient(ctmp, r, vtmp);
  		addcolor(r->rcol, ctmp);
  		flipsurface(r);
  	}
  						/* add direct component */
  	direct(r, dirbrdf, &nd);
  
  	return(1);
  }
  
  
  static int
  setbrdfunc(			/* set up brdf function and variables */
  	BRDFDAT  *np
  )
  {
  	FVECT  vec;
  
  	if (setfunc(np->mp, np->pr) == 0)
  		return(0);	/* it's OK, setfunc says we're done */
  				/* else (re)assign special variables */
  	multv3(vec, np->pnorm, funcxf.xfm);
  	varset("NxP", '=', vec[0]/funcxf.sca);
  	varset("NyP", '=', vec[1]/funcxf.sca);
  	varset("NzP", '=', vec[2]/funcxf.sca);
  	varset("RdotP", '=', np->pdot <= -1.0 ? -1.0 :
  			np->pdot >= 1.0 ? 1.0 : np->pdot);
  	varset("CrP", '=', colval(np->mcolor,RED));
  	varset("CgP", '=', colval(np->mcolor,GRN));
  	varset("CbP", '=', colval(np->mcolor,BLU));
  	return(1);
  }
  