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m_clip.c
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Fri, May 10, 02:31

m_clip.c
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#ifndef lint
static const char RCSid[] = "$Id: m_clip.c,v 2.13 2019/05/04 03:14:04 greg Exp $";
#endif
/*
* m_clip.c - routine for clipped (cut) objects.
*/
#include "copyright.h"
#include "ray.h"
#include "rtotypes.h"
/*
* Clipping objects permit holes and sections to be taken out
* of other objects.
*
* The argument is the clipped materials;
* the first is used to shade upon exit.
*
* In the simple case of the first argument being "void", we
* just add or subtract (depending on whether we're coming or going)
* the list of modifiers to the ray's "newcset", which will then
* take over for "clipset" on penetration. Any surface modifier
* names found in "clipset" will be treated as invisible in raycont().
*
* In the more complicated case of a non-void material as the
* first argument, we have to backtrack up the ray tree to count
* the number of times we've penetrated the front side of one of
* the surfaces we care about. This relies on outward-facing
* surface normals and closed objects, so is somewhat error-prone.
*/
int
m_clip( /* clip objects from ray */
OBJREC *m,
RAY *r
)
{
OBJECT cset[MAXSET+1], *modset;
OBJECT obj, mod;
int entering;
int i;
obj = objndx(m);
if ((modset = (OBJECT *)m->os) == NULL) {
if (m->oargs.nsargs < 1 || m->oargs.nsargs > MAXSET)
objerror(m, USER, "bad # arguments");
modset = (OBJECT *)malloc((m->oargs.nsargs+1)*sizeof(OBJECT));
if (modset == NULL)
error(SYSTEM, "out of memory in m_clip");
modset[0] = 0;
for (i = 0; i < m->oargs.nsargs; i++) {
if (!strcmp(m->oargs.sarg[i], VOIDID))
continue;
if ((mod = lastmod(obj, m->oargs.sarg[i])) == OVOID) {
sprintf(errmsg, "unknown modifier \"%s\"",
m->oargs.sarg[i]);
objerror(m, WARNING, errmsg);
continue;
}
if (inset(modset, mod)) {
objerror(m, WARNING, "duplicate modifier");
continue;
}
insertelem(modset, mod);
}
m->os = (char *)modset;
}
if (r == NULL)
return(0); /* just initializing */
if (r->clipset != NULL)
setcopy(cset, r->clipset);
else
cset[0] = 0;
entering = (r->rod > 0.0); /* entering clipped region? */
for (i = modset[0]; i > 0; i--)
if (entering) {
if (!inset(cset, modset[i])) {
if (cset[0] >= MAXSET)
error(INTERNAL, "set overflow in m_clip");
insertelem(cset, modset[i]);
}
} else if (inset(cset, modset[i]))
deletelem(cset, modset[i]);
/* compute ray value */
r->newcset = cset;
if (strcmp(m->oargs.sarg[0], VOIDID)) {
int inside = 0;
const RAY *rp;
/* check for penetration */
for (rp = r; rp->parent != NULL; rp = rp->parent)
if ((rp->rtype == RAYREFL) & (rp->parent->ro != NULL)
&& inset(modset, rp->parent->ro->omod)) {
if (rp->parent->rod > 0.0)
inside++;
else
inside--;
}
if (inside > 0) { /* we just hit the object */
flipsurface(r);
return(rayshade(r, lastmod(obj, m->oargs.sarg[0])));
}
}
raytrans(r); /* else transfer ray */
return(1);
}

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