OS/2 Professional/OS2PRO194.ISO/os2/graphic/csg_rt/sil.c

C/C++ Source or Header | 1992-07-28 | 4.6 KB | 195 lines

/*

SIL.C  Simple intersection lists

*/

/*...sincludes:0:*/
#include <stdlib.h>
#include <stddef.h>
#include <memory.h>
#include <math.h>
#include "standard.h"
#include "rt.h"
#include "vector.h"
#define    _SIL_
#include "sil.h"

/*...vrt\46\h:0:*/
/*...vvector\46\h:0:*/
/*...vsil\46\h:0:*/
/*...e*/

#define    ZERO(x)        ( ((x)>=-1.0e-100) && ((x)<=1.0e-100) )

/*...st_a_bit_later:0:*/
static double t_a_bit_later(double t)
    {
    return ( t + 100.0 );
    }
/*...e*/
/*...st_a_bit_before:0:*/
static double t_a_bit_before(double t)
    {
    return ( t - 100.0 );
    }
/*...e*/

/*...sintersect_linear_t:0:*/
void    intersect_linear_t(
    double coeff_of_t, double constant_term,
    VECTOR p, VECTOR q,
    void *shapeinfo, double (*value_of_shape)(void *shapeinfo, VECTOR v),
    SIL *sil
    )
    {
    if ( ZERO(coeff_of_t) )
        /* No intersection with solid surface */
        {
        if ( (*value_of_shape)(shapeinfo, p) <= 0.0 )
            /* Completely in solid */
            {
            sil -> n_sis            = 2;
            sil -> sis [0].t        = -INFINITE;
            sil -> sis [0].entering = TRUE;
            sil -> sis [1].t        = INFINITE;
            sil -> sis [1].entering = FALSE;
            }
        else
            /* Completely out of solid */
            sil -> n_sis            = 0;
        }
    else
        /* Intersects solid exactly once */
        {
        double    t = - constant_term / coeff_of_t;

        sil -> n_sis            = 2;
        sil -> sis [0].entering = TRUE;
        sil -> sis [1].entering = FALSE;
        if ( (*value_of_shape)(shapeinfo, t_along_pq(p, q, t_a_bit_later(t))) <= 0.0 )
            /* Entering solid */
            {
            sil -> sis [0].t = t;
            sil -> sis [1].t = INFINITE;
            }
        else
            /* Leaving solid */
            {
            sil -> sis [0].t = -INFINITE;
            sil -> sis [1].t = t;
            }
        }
    }
/*...e*/
/*...sintersect_quadratic_t:0:*/
void    intersect_quadratic_t(
    double qa, double qb, double qc,
    VECTOR p, VECTOR q,
    void *shapeinfo, double (*value_of_shape)(void *shapeinfo, VECTOR v),
    SIL *sil
    )
    {
    double    qs;

    if ( ZERO(qa) )
/*...sdo linear case:16:*/
intersect_linear_t(qb, qc, p, q, shapeinfo, value_of_shape, sil);
/*...e*/
    else if ( (qs = qb*qb - 4.0*qa*qc) < 0.0 )
/*...sno real roots:16:*/
/* No real roots => no intersections, all solid or all empty */
{
if ( (*value_of_shape)(shapeinfo, p) <= 0.0 )
    {
    sil -> n_sis            = 2;
    sil -> sis [0].t        = -INFINITE;
    sil -> sis [0].entering = TRUE;
    sil -> sis [1].t        = INFINITE;
    sil -> sis [1].entering = FALSE;
    }
else
    sil -> n_sis = 0;
}
/*...e*/
    else if ( ZERO(qs) )
/*...sone double root:16:*/
{
double    t = -qb / (qa + qa);
BOOLEAN from_inside = ( (*value_of_shape)(shapeinfo, t_along_pq(p, q, t_a_bit_before(t))) <= 0.0 );
BOOLEAN to_inside   = ( (*value_of_shape)(shapeinfo, t_along_pq(p, q, t_a_bit_later(t))) <= 0.0 );

#define    DUAL_SWITCH(f,t)    (((f)<<1)+(t))

switch ( DUAL_SWITCH(from_inside, to_inside) )
    {
    case DUAL_SWITCH(FALSE, FALSE):        /* Grazing surface */
        sil -> n_sis            = 0;
        break;
    case DUAL_SWITCH(FALSE,  TRUE):        /* Entering solid area */
        sil -> n_sis            = 2;
        sil -> sis [0].t        = t;
        sil -> sis [0].entering = TRUE;
        sil -> sis [1].t        = INFINITE;
        sil -> sis [1].entering = FALSE;
        break;
    case DUAL_SWITCH( TRUE, FALSE):        /* Leaving solid area */
        sil -> n_sis            = 2;
        sil -> sis [0].t        = -INFINITE;
        sil -> sis [0].entering = TRUE;
        sil -> sis [1].t        = t;
        sil -> sis [1].entering = FALSE;
        break;
    case DUAL_SWITCH( TRUE,  TRUE):        /* Never left solid area */
        sil -> n_sis            = 2;
        sil -> sis [0].t        = -INFINITE;
        sil -> sis [0].entering = TRUE;
        sil -> sis [1].t        = INFINITE;
        sil -> sis [1].entering = FALSE;
        break;
    }
}
/*...e*/
    else
/*...stwo roots:16:*/
{
double    rooted = sqrt(qs);
double    t1 = (-qb - rooted) / (qa + qa);
double    t2 = (-qb + rooted) / (qa + qa);

if ( t1 > t2 )
    /* Ensure t1 is lower than t2 */
    {
    double    t = t1;

    t1 = t2;
    t2 = t;
    }

if ( (*value_of_shape)(shapeinfo, t_along_pq(p, q, (t1 + t2) * 0.5)) <= 0.0 )
    /* Middle part is the solid part */
    {
    sil -> n_sis            = 2;
    sil -> sis [0].t        = t1;
    sil -> sis [0].entering = TRUE;
    sil -> sis [1].t        = t2;
    sil -> sis [1].entering = FALSE;
    }
else
    /* Regions before and after middle part are the solid parts */
    {
    sil -> n_sis            = 4;
    sil -> sis [0].t        = -INFINITE;
    sil -> sis [0].entering = TRUE;
    sil -> sis [1].t        = t1;
    sil -> sis [1].entering = FALSE;
    sil -> sis [2].t        = t2;
    sil -> sis [2].entering = TRUE;
    sil -> sis [3].t        = INFINITE;
    sil -> sis [3].entering = FALSE;
    }
}
/*...e*/
    }
/*...e*/