t_func.c
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	#ifndef lint
	static const char RCSid[] = "$Id: t_func.c,v 2.10 2014/07/08 18:25:00 greg Exp $";
	#endif
	/*
	* t_func.c - routine for procedural textures.
	*/

	#include "copyright.h"

	#include "ray.h"
	#include "func.h"
	#include "rtotypes.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.
	*/


	int
	t_func( /* compute texture for ray */
	OBJREC *m,
	RAY *r
	)
	{
	FVECT disp;
	double d;
	MFUNC *mf;
	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 == EDOM \|\| errno == ERANGE) {
	objerror(m, WARNING, "compute error");
	return(0);
	}
	}
	if (mf->fxp != &unitxf)
	multv3(disp, disp, mf->fxp->xfm);
	if (r->rox != NULL) {
	multv3(disp, disp, r->rox->f.xfm);
	d = 1.0 / (mf->fxp->sca * r->rox->f.sca);
	} else
	d = 1.0 / mf->fxp->sca;
	VSUM(r->pert, r->pert, disp, d);
	return(0);
	}