/* Copyright (c) 1991 Regents of the University of California */

#ifndef lint
static char SCCSid[] = "@(#)t_func.c 2.2 11/25/91 LBL";
#endif

/*
 *  t_func.c - routine for procedural textures.
 *
 *     4/8/86
 */

#include  "ray.h"

#include  "func.h"

/*
 *	A procedural texture perturbs the surface normal
 *  at the point of intersection with an object.  It has
 *  the form:
 *
 *	modifier texfunc name
 *	4+ xvarname yvarname zvarname filename xf
 *	0
 *	n A1 A2 ..
 *
 *  Filename is the name of the file where the variable definitions
 *  can be found.  The list of real arguments can be accessed by
 *  definitions in the file.  The xf is a transformation to get
 *  from the original coordinates to the current coordinates.
 */


t_func(m, r)			/* compute texture for ray */
register OBJREC  *m;
register RAY  *r;
{
	FVECT  disp;
	double  d;
	register MFUNC  *mf;
	register int  i;

	if (m->oargs.nsargs < 4)
		objerror(m, USER, "bad # arguments");
	mf = getfunc(m, 3, 0x7, 1);
	setfunc(m, r);
	errno = 0;
	for (i = 0; i < 3; i++) {
		disp[i] = evalue(mf->ep[i]);
		if (errno) {
			objerror(m, WARNING, "compute error");
			return;
		}
	}
	if (mf->f != &unitxf)
		multv3(disp, disp, mf->f->xfm);
	if (r->rox != NULL) {
		multv3(disp, disp, r->rox->f.xfm);
		d = 1.0 / (mf->f->sca * r->rox->f.sca);
	} else
		d = 1.0 / mf->f->sca;
	for (i = 0; i < 3; i++)
		r->pert[i] += disp[i] * d;
}