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LIBRT(3)			    BRL-CAD			      LIBRT(3)

NAME
       librt - library for raytracing an MGED database

SYNOPSIS
       #include	"vmath.h"
       #include	"raytrace.h"

       This file seems to be out of date with the sources. Consult the headers
       for up-to-date information. Use the below interface documentation at
       your own	discretion. extern struct rt_functab rt_functab[];

       extern struct rt_g rt_g;

       struct rt_i *rt_dirbuild(char * mged_file_name, char * buf, int len);

       int rt_gettree(struct rt_i * rtip, char * object_name);

       void rt_prep(struct rt_i	* rtip);

       int rt_shootray(struct application * ap);

       void rt_prep_timer(void);

       double rt_read_timer(char * buf,	int len);

       void rt_pr_partitions(struct rt_i *rtip struct partition	* phead,
			     char * title, void	rt_pr_seg( segp	));

			     struct seg	*segp;

       struct soltab *rt_find_solid(void);

DESCRIPTION
       rt_dirbuild opens mged_file_name	and builds a directory for quick
       lookup of objects.  rt_dirbuild returns a pointer to a struct rt_i on
       success (often called ``rtip''),	or RTI_NULL on failure (such as	being
       unable to open the named	database). This	pointer	must be	saved, as it
       is a required parameter to rt_gettree. The user-supplied	buffer buf is
       filled with up to len characters	of information from the	first title
       record in the database. If it is	desired	for "air" objects to be
       reported	as "hits" during ray-tracing, then the useair member of	the
       struct rt_i must	be set before the first	call to	rt_gettree.

       All objects (groups and regions)	which are to be	included in the
       description to be raytraced must	be preprocessed	with rt_gettree, which
       returns -1 for failure and 0 for	success. This function can be called
       as many times as	required. Be certain to	pass the struct	rt_i pointer
       from rt_dirbuild	each time.

       After the last rt_gettree call, rt_prep can be called to	complete the
       preparation of internal data structures.	If rt_prep is not explicitly
       called, it will be indirectly invoked by	the first use of rt_shootray.

       To fire a ray at	the model, an application structure must be prepared
       and its address passed to rt_shootray. Note that	it is mandatory	that
       you provide values for a_ray.r_pt (the starting point of	the ray	to be
       fired), a_ray.r_dir (a unit-length direction vector), a_hit (address of
       user-supplied hit routine), a_miss (address of user-supplied miss
       routine), a_overlap (address of user-supplied overlap routine; may be
       null), a_rt_i (struct rt_i pointer, from	rt_dirbuild), a_onehit (flag
       controlling stop	after first hit), a_level (recursion level, just for
       diagnostic printing), and a_resource (address of	resource structure;
       may be null).

       To obtain a report of CPU usage for a portion or	portions of your
       program,	frame the statements with calls	to rt_prep_timer and
       rt_read_timer. Each call	to rt_prep_timer resets	the timing process,
       after which rt_read_timer can be	called to get a	double which is	the
       elapsed CPU time	in seconds since rt_prep_timer was last	called.	In
       addition, up to len bytes of system-specific detailing of resource
       consumption is placed in	the user-supplied buffer buf.

       bu_bomb can be used to exit your	program	with msg printed on the
       standard	error output.

WARNING
       Librt is	designed to run	in parallel on some multiprocessor machines.
       On some such machines system calls must be semaphore protected.

       Dynamic memory handling in applications using librt should use the
       functions provided by libbu instead of the usual	system runtime library
       routines. The libbu versions do not return to the caller	unless they
       succeed.	If they	fail, they call	bu_bomb	with their last	argument (str)
       as the parameter. The string parameter usually indicates	the purpose of
       the memory being	allocated.

EXIT CODE
       All truly fatal errors detected by the library use bu_bomb to exit with
       a status	of 12.

DEFINITION
       RPP - Rectangular ParallelePiped. A region of space defined by minimum
       and maximum values in X,	Y, and Z. RPPs are used	by librt as bounding
       volumes for solids.

DISCUSSION
       You should study	the structures in raytrace.h, in particular, the
       application structure, the partition structure and its component
       structures to get an idea of what information is	handed to/from
       rt_shootray.  rt_shootray may be	called recursively from	your a_hit
       routine (good for doing bounced rays). If you only care about the first
       object hit along	the path of the	ray, set the a_onehit flag in the
       application structure before calling rt_shootray.  rt_shootray returns
       the return value	of the user-supplied hit or miss function that it
       called.

       If the ray intersects the model,	the a_hit routine is called with a
       pointer to the application structure and	a pointer to a linked list of
       ray partitions (struct partition). Within each partition	are seg	(solid
       segment)	and hit	(intersection with evaluated region) structure
       pointers	for the	places where the ray enters and	leaves this partition
       of space.  pt_inhit.hit_dist is the parametric distance at which	the
       ray enters the partition, and pt_outhit.hit_dist	is the parametric
       distance	at which the ray leaves. Note that while the hit structure
       contains	hit_point and hit_norm elements, they are not computed by
       rt_shootray. If these are needed, they can be filled in by using	the
       RT_HIT_NORMAL macro; if surface curvature information is	needed,	it can
       be obtained by using the	RT_CURVE macro after RT_HIT_NORMAL; if only
       the hit_point is	needed,	it can be filled in by using the VJOIN1	macro
       (see the	following example).

       If the ray contains any overlaps	(partitions claimed by two or more
       regions)	the a_overlap routine is called	for each such partition	with
       pointers	to the application structure, the overlap partition, two
       regions,	and the	remaining partitions along the ray. If the a_overlap
       member is null, librt uses a default overlap handler. Additionally,
       librt provides the routine

       If the ray does not intersect the model,	the a_miss routine is called
       with a pointer to the application structure.

       Helpful in generating a grid of ray origins, the	bounding RPP of	the
       model is	computed by rt_gettree and is stored in	rtip-_mdl_min and
       rtip-_mdl_max.

EXAMPLE
       A program can be	loaded as follows:

       $ cc -I/usr/brlcad/include main.c /usr/brlcad/lib/librt.a
       -l_system-specific_ -lm

       where _system-specific_ indicates libraries required on a particular
       architecture. The table below indicates which system specific libraries
       are necessary on	a particular architecture.

       Architecture Librarie(s)	Alliant	FX/8 -lcvec -lcommon Alliant FX/2800
       -lcommon	SGI 4D -lmpc Cray(X/Y) -L/lib/multi -lu	-lio Cray2 -lmt	Encore
       Multi-Max -lpp

       Here is a portion of a hypothetical program which uses the library:

	   #include <vmath.h>
	   #include <raytrace.h>
	   main( argc, argv )
	   int argc;
	   char	*argv[];
	   {
		static int do_if_hit(),	do_if_miss();	/* Application routines	*/
		register int h,	v;
		int grid_sz;
		struct application ap;	      /* Set up	for rt_shootray() */
		struct rt_i *rtip;
		/* ... */

		/* Build the directory.	 */
		rtip = rt_dirbuild( argv[bu_optind++] );

		/* Load	the desired portion of the model. */
		while( argv[bu_optind] != NULL )
		     rt_gettree( rtip, argv[bu_optind++] );

		ap.a_hit = do_if_hit;	      /* Supply	routine	for hit	*/
		ap.a_miss = do_if_missed;     /* Supply	routine	for miss */
		ap.a_overlap = 0;
		ap.a_rt_i = rtip;
		ap.a_level = 0;
		ap.a_onehit = 0;	 /* Return all objects along ray */
		ap.a_resource =	0;

		for( v = 0; v <	grid_sz; ++v )	   /* For each scanline	*/
		     for( h = 0; h < grid_sz; ++h )  {
			  /* Set up ray	origin.	*/
			  VMOVE( ap.a_ray.r_pt,	get_grid( h, v ) );
			  /* Compute ray direction. */
			  VMOVE( ap.a_ray.r_dir, get_dir( h, v ) );
			  /* Must be unit vector. */
			  VUNITIZE( ap.a_ray.r_dir );
			  (void) rt_shootray( &ap );
		     }
		/* ... */
	   }

	   static int
	   do_if_hit( ap, PartHeadp )
	   register struct application *ap;
	   struct partition *PartHeadp;
	   {
		extern void put_component();
		struct curvature incurv;
		register struct	partition *pp;

		for( pp	= PartHeadp->pt_forw; pp != PartHeadp; pp = pp->pt_forw	)  {

		     /*	Fill in	all inhit info,	but just the exit location for outhit. */
		     RT_HIT_NORMAL(pp->pt_inhit->hit_normal, pp->pt_inhit, pp->pt_inseg->seg_stp, &ap->a_ray, pp->pt_inflip);
		     RT_CURVE( &incurv,	pp->pt_inhit, pp->pt_inseg->seg_stp );
		     VJOIN1( pp->pt_outhit->hit_point, ap->a_ray.r_pt,
			       pp->pt_outhit->hit_dist,	ap->a_ray.r_dir	);

		     /*	Do something based on information in partition structure
		      *	  such as output a shotline component data record.
		      */
		     put_component( pp->pt_inhit, &incurv, pp->pt_outhit );
		     /*	... */
		}
		return	  1;		 /* Report hit to main routine */
	   }

	   static int
	   do_if_missed( ap )
	   register struct application *ap;
	   {
		return	  0;		 /* Report miss	to main	routine	*/
	   }

SEE ALSO
       mged(1B), rt(1B).

DIAGNOSTICS
       "rt_malloc: malloc failure", if librt is	unable to allocate memory with
       malloc. ``rt_???: read error'', if an error or EOF occurs while reading
       from the	model database.	"unexpected SIGFPE!" when a floating point
       error occurs. (The rootfinder traps SIGFPE, but SIGFPE elsewhere	is
       unexpected.) "rt_shootray: zero length dir vector" when the a_ray.r_dir
       vector is not unit length. "rt_gettree called again after rt_prep!"
       when an attempt is made to add more sub-trees to	the active model after
       calling rt_prep (or after firing	the first ray).	"rt_prep:
       re-invocation" when rt_prep is called more than once. "rt_prep: no
       solids to prep" when there are no valid solids in the model.

       The LIBRT_DEBUG environment variable may	be set to the hexadecimal bit
       vector as described by the DEBUG_* flags	listed in the raytrace.h
       header. Similarly, many LIBRT applications provide a "-x	#"
       command-line option which will take precedence over the environment
       variable.

       The LIBRT_V4FLIP	environment variable may be set	to a true or false
       value to	respectively force or disable endianness interpretation	of v4
       geometry	database files.	The default behavior is	to automatically
       detect whether flipping the endian interpretation will help LIBRT read
       a binary-incompatible v4	geometry database file.	Setting	LIBRT_V4FLIP
       will override automatic detection.

       The LIBRT_BOT_MINTIE environment	variable may be	set to the minimum
       number of faces a BoT primitive must have to exercise the Triangle
       Intersection Engine (TIE) raytrace evaluation. A	value less than	or
       equal to	zero will utilize traditional BoT raytracing instead of	TIE.

BUGS
       On a VAX, the rootfinder	detects	"hard" cases by	taking a SIGFPE	and
       retrying	with a slower but more stable algorithm. This is unfortunate.

AUTHOR
       BRL-CAD Team

COPYRIGHT
       This software is	Copyright (c) 1986-2013	United States Government as
       represented by the U.S. Army Research Laboratory. All rights reserved.

BUG REPORTS
       Reports of bugs or problems should be submitted via electronic mail to
       <devs@brlcad.org>.

BRL-CAD				  07/08/2017			      LIBRT(3)

NAME | SYNOPSIS | DESCRIPTION | WARNING | EXIT CODE | DEFINITION | DISCUSSION | EXAMPLE | SEE ALSO | DIAGNOSTICS | BUGS | AUTHOR | COPYRIGHT | BUG REPORTS

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