/*
 * "A Simple Method for Box-Sphere Intersection Testing",
 *  by Jim Arvo, in "Graphics Gems", Academic Press, 1990.
 *
 * This routine tests for intersection between an n-dimensional             
 * axis-aligned box and an n-dimensional sphere.  The mode argument       
 * indicates whether the objects are to be regarded as surfaces or        
 * solids.  The values are:                                               
 *                                                                         
 * mode   meaning
 *                                                                         
 *  0     Hollow Box, Hollow Sphere                                     
 *  1     Hollow Box, Solid  Sphere
 *  2     Solid  Box, Hollow Sphere                                     
 *  3     Solid  Box, Solid  Sphere                                     
 *                                                                         
 */

#include "GraphicsGems.h"

int Box_Sphere_Intersect( n, Bmin, Bmax, C, r, mode )
int    n;       /* The dimension of the space.           */
float  Bmin[];  /* The minimum of the box for each axis. */
float  Bmax[];  /* The maximum of the box for each axis. */
float  C[];     /* The sphere center in n-space.         */
float  r;       /* The radius of the sphere.             */
int    mode;    /* Selects hollow or solid.              */
    {
    float  a, b;
    float  dmin, dmax;
    float  r2 = SQR( r );
    int    i, face;

    switch( mode )
        {
        case 0: /* Hollow Box and Hollow Sphere */
            dmin = 0;
            dmax = 0;
            face = FALSE;
            for( i = 0; i < n; i++ ) {
                a = SQR( C[i] - Bmin[i] );
                b = SQR( C[i] - Bmax[i] );
                dmax += MAX( a, b );
                if( C[i] < Bmin[i] ) {
                    face = TRUE;
                    dmin += a;
                    }
                else if( C[i] > Bmax[i] ) {
                    face = TRUE;
                    dmin += b;
                    }
                else if( MIN( a, b ) <= r2 ) face = TRUE;
                }
            if( face && ( dmin <= r2 ) && ( r2 <= dmax ) ) return TRUE;
            break;

        case 1: /* Hollow Box and Solid Sphere */
            dmin = 0;
            face = FALSE;
            for( i = 0; i < n; i++ ) {
                if( C[i] < Bmin[i] ) {
                    face = TRUE;
                    dmin += SQR( C[i] - Bmin[i] );
                    }
                else if( C[i] > Bmax[i] ) {
                    face = TRUE;
                    dmin += SQR( C[i] - Bmax[i] );     
                    }
                else if( C[i] - Bmin[i] <= r ) face = TRUE;
                else if( Bmax[i] - C[i] <= r ) face = TRUE;
                }
            if( face && ( dmin <= r2 ) ) return TRUE;
            break;

        case 2: /* Solid Box and Hollow Sphere */
            dmax = 0;
            dmin = 0;
            for( i = 0; i < n; i++ ) {
                a = SQR( C[i] - Bmin[i] );
                b = SQR( C[i] - Bmax[i] );
                dmax += MAX( a, b );
                if( C[i] < Bmin[i] ) dmin += a; else
                if( C[i] > Bmax[i] ) dmin += b;
                }
            if( dmin <= r2 && r2 <= dmax ) return TRUE;
            break;

        case 3: /* Solid Box and Solid Sphere */
            dmin = 0;
            for( i = 0; i < n; i++ ) {
                if( C[i] < Bmin[i] ) dmin += SQR( C[i] - Bmin[i] ); else
                if( C[i] > Bmax[i] ) dmin += SQR( C[i] - Bmax[i] );     
                }
            if( dmin <= r2 ) return TRUE;
            break;
  
        } /* end switch */

    return FALSE;
    }