raybox.c

Graphics Gems 源码 a collection of algorithms, programs, and mathematical techniques for the computer

/* 
Fast Ray-Box Intersection
by Andrew Woo
from "Graphics Gems", Academic Press, 1990
*/

#include "GGems.h"

#define NUMDIM	3
#define RIGHT	0
#define LEFT	1
#define MIDDLE	2

char HitBoundingBox(minB,maxB, origin, dir,coord)
double minB[NUMDIM], maxB[NUMDIM];		/*box */
double origin[NUMDIM], dir[NUMDIM];		/*ray */
double coord[NUMDIM];				/* hit point */
{
	char inside = TRUE;
	char quadrant[NUMDIM];
	register int i;
	int whichPlane;
	double maxT[NUMDIM];
	double candidatePlane[NUMDIM];

	/* Find candidate planes; this loop can be avoided if
   	rays cast all from the eye(assume perpsective view) */
	for (i=0; i<NUMDIM; i++)
		if(origin[i] < minB[i]) {
			quadrant[i] = LEFT;
			candidatePlane[i] = minB[i];
			inside = FALSE;
		}else if (origin[i] > maxB[i]) {
			quadrant[i] = RIGHT;
			candidatePlane[i] = maxB[i];
			inside = FALSE;
		}else	{
			quadrant[i] = MIDDLE;
		}

	/* Ray origin inside bounding box */
	if(inside)	{
		coord = origin;
		return (TRUE);
	}


	/* Calculate T distances to candidate planes */
	for (i = 0; i < NUMDIM; i++)
		if (quadrant[i] != MIDDLE && dir[i] !=0.)
			maxT[i] = (candidatePlane[i]-origin[i]) / dir[i];
		else
			maxT[i] = -1.;

	/* Get largest of the maxT's for final choice of intersection */
	whichPlane = 0;
	for (i = 1; i < NUMDIM; i++)
		if (maxT[whichPlane] < maxT[i])
			whichPlane = i;

	/* Check final candidate actually inside box */
	if (maxT[whichPlane] < 0.) return (FALSE);
	for (i = 0; i < NUMDIM; i++)
		if (whichPlane != i) {
			coord[i] = origin[i] + maxT[whichPlane] *dir[i];
			if ((quadrant[i] == RIGHT && coord[i] < minB[i]) ||
			   (quadrant[i] == LEFT && coord[i] > maxB[i]))
			   return (FALSE);	/* outside box */
			}else {
				coord[i] = candidatePlane[i];
			}
	return (TRUE);				/* ray hits box */
}