Example Application

<source lang="c"> /* R T E X A M P L E . C

* BRL-CAD
*
* Copyright (c) 2004-2013 United States Government as represented by
* the U.S. Army Research Laboratory.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public License
* version 2.1 as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this file; see the file named COPYING for more
* information.
*/

/** @file rt/rtexample.c

*
* This is a heavily commented example of a program that uses librt to
* shoot a single ray at some geometry in a .g database.
*
* The primary BRL-CAD ray-tracing API consists of calls to the
* function rt_shootray().  This function takes a single argument, the
* address of a data structure called the "application" structure.
* This data structure contains crucial information, such as the
* origin and direction of the ray to be traced, what to do if the ray
* hits geometry, or what to do if it misses everything.  While the
* application struct is a large and somewhat complex looking, (it is
* defined in the raytrace.h header) there are really very few items
* in it which the application programmer must know about. These are:
*
*   a_rt_i	The "raytrace instance" obtained via rt_dirbuild()
*   a_ray	The ray origin and direction to be shot
*   a_hit	A callback function for when the ray encounters geometry
*   a_miss	A callback function for when the ray misses everything
*
* Most of the work an application performs will be done in the "hit"
* routine.  This user-supplied routine gets called deep inside the
* raytracing library via the rt_shootray() function.  It is provided
* with 3 parameters:
*
*   ap		Pointer to the application structure passed to rt_shootray()
*   PartHeadp	List of ray "partitions" which represent geometry hit
*   segp	List of ray "segments" that comprised partitions
*
* Most applications can ignore the last parameter.  The PartHeadp
* parameter is a linked-list of "partition" structures (defined in
* the raytrace.h header).  It is the job of the "hit" routine to
* process these ray/object intersections to do the work of the
* application.
*
* This file is part of the default compile in source distributions of
* BRL-CAD and is usually installed or provided via binary and source
* distributions.  To compile this example from a binary install:
*
* cc -I/usr/brlcad/include/brlcad -L/usr/brlcad/lib -o rtexample rtexample.c -lbu -lrt -lm
*
* Jump to the START HERE section below for main().
*/

1. include "common.h"

1. include <stdlib.h>
2. include <math.h>
3. include <string.h>
4. include <stdio.h>

1. include "vmath.h" /* vector math macros */
2. include "raytrace.h" /* librt interface definitions */

/**

* rt_shootray() was told to call this on a hit.
*
* This callback routine utilizes the application structure which
* describes the current state of the raytrace.
*
* This callback routine is provided a circular linked list of
* partitions, each one describing one in and out segment of one
* region for each region encountered.
*
* The 'segs' segment list is unused in this example.
*/

int hit(struct application *ap, struct partition *PartHeadp, struct seg *UNUSED(segs)) {

   /* iterating over partitions, this will keep track of the current
    * partition we're working on.
    */
   struct partition *pp;

   /* will serve as a pointer for the entry and exit hitpoints */
   struct hit *hitp;

   /* will serve as a pointer to the solid primitive we hit */
   struct soltab *stp;

   /* will contain surface curvature information at the entry */
   struct curvature cur = RT_CURVATURE_INIT_ZERO;

   /* will contain our hit point coordinate */
   point_t pt;

   /* will contain normal vector where ray enters geometry */
    vect_t inormal;

   /* will contain normal vector where ray exits geometry */
   vect_t onormal;

   /* iterate over each partition until we get back to the head.
    * each partition corresponds to a specific homogeneous region of
    * material.
    */
   for (pp=PartHeadp->pt_forw; pp != PartHeadp; pp = pp->pt_forw) {

/* print the name of the region we hit as well as the name of * the primitives encountered on entry and exit. */ bu_log("\n--- Hit region %s (in %s, out %s)\n", pp->pt_regionp->reg_name, pp->pt_inseg->seg_stp->st_name, pp->pt_outseg->seg_stp->st_name );

/* entry hit point, so we type less */ hitp = pp->pt_inhit;

/* construct the actual (entry) hit-point from the ray and the * distance to the intersection point (i.e., the 't' value). */ VJOIN1(pt, ap->a_ray.r_pt, hitp->hit_dist, ap->a_ray.r_dir);

/* primitive we encountered on entry */ stp = pp->pt_inseg->seg_stp;

/* compute the normal vector at the entry point, flipping the * normal if necessary. */ RT_HIT_NORMAL(inormal, hitp, stp, &(ap->a_ray), pp->pt_inflip);

/* print the entry hit point info */ rt_pr_hit(" In", hitp); VPRINT( " Ipoint", pt); VPRINT( " Inormal", inormal);

/* This next macro fills in the curvature information which * consists on a principle direction vector, and the inverse * radii of curvature along that direction and perpendicular * to it. Positive curvature bends toward the outward * pointing normal. */ RT_CURVATURE(&cur, hitp, pp->pt_inflip, stp);

/* print the entry curvature information */ VPRINT("PDir", cur.crv_pdir); bu_log(" c1=%g\n", cur.crv_c1); bu_log(" c2=%g\n", cur.crv_c2);

/* exit point, so we type less */ hitp = pp->pt_outhit;

/* construct the actual (exit) hit-point from the ray and the * distance to the intersection point (i.e., the 't' value). */ VJOIN1(pt, ap->a_ray.r_pt, hitp->hit_dist, ap->a_ray.r_dir);

/* primitive we exited from */ stp = pp->pt_outseg->seg_stp;

/* compute the normal vector at the exit point, flipping the * normal if necessary. */ RT_HIT_NORMAL(onormal, hitp, stp, &(ap->a_ray), pp->pt_outflip);

/* print the exit hit point info */ rt_pr_hit(" Out", hitp); VPRINT( " Opoint", pt); VPRINT( " Onormal", onormal);

   }

   /* A more complicated application would probably fill in a new
    * local application structure and describe, for example, a
    * reflected or refracted ray, and then call rt_shootray() for
    * those rays.
    */

   /* Hit routine callbacks generally return 1 on hit or 0 on miss.
    * This value is returned by rt_shootray().
    */
   return 1;

}

/**

* This is a callback routine that is invoked for every ray that
* entirely misses hitting any geometry.  This function is invoked by
* rt_shootray() if the ray encounters nothing.
*/

int miss(struct application *UNUSED(ap)) {

   bu_log("missed\n");
   return 0;

}

/**

* START HERE
*
* This is where it all begins.
*/

int main(int argc, char **argv) {

   /* Every application needs one of these.  The "application"
    * structure carries information about how the ray-casting should
    * be performed.  Defined in the raytrace.h header.
    */
   struct application	ap;

   /* The "raytrace instance" structure contains definitions for
    * librt which are specific to the particular model being
    * processed.  One copy exists for each model.  Defined in
    * the raytrace.h header and is returned by rt_dirbuild().
    */
   static struct rt_i *rtip;

   /* optional parameter to rt_dirbuild() that can be used to capture
    * a title if the geometry database has one set.
    */
   char title[1024] = {0};

   /* Check for command-line arguments.  Make sure we have at least a
    * geometry file and one geometry object on the command line.
    */
   if (argc < 3) {

bu_exit(1, "Usage: %s model.g objects...\n", argv[0]);

   }

   /* Load the specified geometry database (i.e., a ".g" file).
    * rt_dirbuild() returns an "instance" pointer which describes the
    * database to be raytraced.  It also gives you back the title
    * string if you provide a buffer.  This builds a directory of the
    * geometry (i.e., a table of contents) in the file.
    */
   rtip = rt_dirbuild(argv[1], title, sizeof(title));
   if (rtip == RTI_NULL) {

bu_exit(2, "Building the database directory for [%s] FAILED\n", argv[1]);

   }

   /* Display the geometry database title obtained during
    * rt_dirbuild if a title is set.
    */
   if (title[0]) {

bu_log("Title:\n%s\n", title);

   }

   /* Walk the geometry trees.  Here you identify any objects in the
    * database that you want included in the ray trace by iterating
    * of the object names that were specified on the command-line.
    */
   while (argc > 2)  {

if (rt_gettree(rtip, argv[2]) < 0) bu_log("Loading the geometry for [%s] FAILED\n", argv[2]); argc--; argv++;

   }

   /* This next call gets the database ready for ray tracing.  This
    * causes some values to be precomputed, sets up space
    * partitioning, computes bounding volumes, etc.
    */
   rt_prep_parallel(rtip, 1);

   /* initialize all values in application structure to zero */
   RT_APPLICATION_INIT(&ap);

   /* your application uses the raytrace instance containing the
    * geometry we loaded.  this describes what we're shooting at.
    */
   ap.a_rt_i = rtip;

   /* stop at the first point of intersection or shoot all the way
    * through (defaults to 0 to shoot all the way through).
    */
   ap.a_onehit = 0;

   /* Set the ray start point and direction rt_shootray() uses these
    * two to determine what ray to fire.  In this case we simply
    * shoot down the z axis toward the origin from 10 meters away.
    *
    * It's worth nothing that librt assumes units of millimeters.
    * All geometry is stored as millimeters regardless of the units
    * set during editing.  There are libbu routines for performing
    * unit conversions if desired.
    */
   VSET(ap.a_ray.r_pt, 0.0, 0.0, 10000.0);
   VSET(ap.a_ray.r_dir, 0.0, 0.0, -1.0);

   /* Simple debug printing */
   VPRINT("Pnt", ap.a_ray.r_pt);
   VPRINT("Dir", ap.a_ray.r_dir);

   /* This is what callback to perform on a hit. */
   ap.a_hit = hit;

   /* This is what callback to perform on a miss. */
   ap.a_miss = miss;

   /* Shoot the ray. */
   (void)rt_shootray(&ap);

   /* A real application would probably set up another ray and fire
    * again or do something a lot more complex in the callbacks.
    */

   return 0;

}

/*

* Local Variables:
* mode: C
* tab-width: 8
* indent-tabs-mode: t
* c-file-style: "stroustrup"
* End:
* ex: shiftwidth=4 tabstop=8
*/

</source>