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o_mesh.c
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Fri, May 3, 11:30

o_mesh.c
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#ifndef lint
static const char RCSid[] = "$Id: o_mesh.c,v 2.15 2019/03/01 02:03:33 greg Exp $";
#endif
/*
* Routines for computing ray intersections with meshes.
*
* Intersection with a triangle mesh is based on Segura and Feito's
* WSCG 2001 paper, "Algorithms to Test Ray-Triangle Intersection,
* Comparative Study." This method avoids additional storage
* requirements, floating divides, and allows some savings by
* caching ray-edge comparisons that are otherwise repeated locally
* in typical mesh geometries. (This is our own optimization.)
*
* The code herein is quite similar to that in o_instance.c, the
* chief differences being the custom triangle intersection routines
* and the fact that an "OBJECT" in the mesh octree is not an index
* into the Radiance OBJREC list, but a mesh triangle index. We still
* utilize the standard octree traversal code by setting the hitf
* function pointer in the RAY struct to our custom mesh_hit() call.
*/
#include "copyright.h"
#include <string.h>
#include "ray.h"
#include "mesh.h"
#include "tmesh.h"
#include "rtotypes.h"
#define EDGE_CACHE_SIZ 251 /* length of mesh edge cache */
#define curmi (edge_cache.mi)
#define curmsh (curmi->msh)
/* Cache of signed volumes for this ray and this mesh */
struct EdgeCache {
OBJREC *o; /* mesh object */
MESHINST *mi; /* current mesh instance */
struct EdgeSide {
int32 v1i, v2i; /* vertex indices (lowest first) */
short signum; /* signed volume */
} cache[EDGE_CACHE_SIZ];
} edge_cache;
static void
prep_edge_cache(o) /* get instance and clear edge cache */
OBJREC *o;
{
/* get mesh instance */
edge_cache.mi = getmeshinst(edge_cache.o = o, IO_ALL);
/* clear edge cache */
memset((void *)edge_cache.cache, '\0', sizeof(edge_cache.cache));
}
static int
volume_sign(r, v1, v2) /* get signed volume for ray and edge */
RAY *r;
int32 v1, v2;
{
int reversed = 0;
struct EdgeSide *ecp;
if (v1 > v2) {
int32 t = v2; v2 = v1; v1 = t;
reversed = 1;
}
ecp = &edge_cache.cache[((v2<<11 ^ v1) & 0x7fffffff) % EDGE_CACHE_SIZ];
if ((ecp->v1i != v1) | (ecp->v2i != v2)) {
MESHVERT tv1, tv2; /* compute signed volume */
FVECT v2d;
double vol;
if (!getmeshvert(&tv1, edge_cache.mi->msh, v1, MT_V) |
!getmeshvert(&tv2, edge_cache.mi->msh, v2, MT_V))
objerror(edge_cache.o, INTERNAL,
"missing mesh vertex in volume_sign");
VSUB(v2d, tv2.v, r->rorg);
vol = (tv1.v[0] - r->rorg[0]) *
(v2d[1]*r->rdir[2] - v2d[2]*r->rdir[1]);
vol += (tv1.v[1] - r->rorg[1]) *
(v2d[2]*r->rdir[0] - v2d[0]*r->rdir[2]);
vol += (tv1.v[2] - r->rorg[2]) *
(v2d[0]*r->rdir[1] - v2d[1]*r->rdir[0]);
/* don't generate 0 */
ecp->signum = vol > .0 ? 1 : -1;
ecp->v1i = v1;
ecp->v2i = v2;
}
return(reversed ? -ecp->signum : ecp->signum);
}
static void
mesh_hit(oset, r) /* intersect ray with mesh triangle(s) */
OBJECT *oset;
RAY *r;
{
int32 tvi[3];
int sv1, sv2, sv3;
MESHVERT tv[3];
OBJECT tmod;
FVECT va, vb, nrm;
double d;
int i;
/* check each triangle */
for (i = oset[0]; i > 0; i--) {
if (!getmeshtrivid(tvi, &tmod, curmsh, oset[i]))
objerror(edge_cache.o, INTERNAL,
"missing triangle vertices in mesh_hit");
sv1 = volume_sign(r, tvi[0], tvi[1]);
sv2 = volume_sign(r, tvi[1], tvi[2]);
if (sv1 != sv2) /* compare volume signs */
continue;
sv3 = volume_sign(r, tvi[2], tvi[0]);
if (sv2 != sv3)
continue;
/* compute intersection */
getmeshvert(&tv[0], curmsh, tvi[0], MT_V);
getmeshvert(&tv[1], curmsh, tvi[1], MT_V);
getmeshvert(&tv[2], curmsh, tvi[2], MT_V);
VSUB(va, tv[0].v, tv[2].v);
VSUB(vb, tv[1].v, tv[0].v);
VCROSS(nrm, va, vb);
d = DOT(r->rdir, nrm);
if (d == 0.0)
continue; /* ray is tangent */
VSUB(va, tv[0].v, r->rorg);
d = DOT(va, nrm) / d;
if ((d <= FTINY) | (d >= r->rot))
continue; /* not good enough */
r->robj = oset[i]; /* else record hit */
r->ro = edge_cache.o;
r->rot = d;
VSUM(r->rop, r->rorg, r->rdir, d);
VCOPY(r->ron, nrm);
/* normalize(r->ron) called & r->rod set in o_mesh() */
}
}
int
o_mesh( /* compute ray intersection with a mesh */
OBJREC *o,
RAY *r
)
{
RAY rcont;
int flags;
MESHVERT tv[3];
OBJECT tmod;
RREAL wt[3];
int i;
/* get the mesh instance */
prep_edge_cache(o);
/* copy and transform ray */
rcont = *r;
multp3(rcont.rorg, r->rorg, curmi->x.b.xfm);
multv3(rcont.rdir, r->rdir, curmi->x.b.xfm);
for (i = 0; i < 3; i++)
rcont.rdir[i] /= curmi->x.b.sca;
rcont.rmax *= curmi->x.b.sca;
/* clear and trace ray */
rayclear(&rcont);
rcont.hitf = mesh_hit;
if (!localhit(&rcont, &curmi->msh->mcube))
return(0); /* missed */
if (rcont.rot * curmi->x.f.sca >= r->rot)
return(0); /* not close enough */
/* transform ray back */
r->rot = rcont.rot * curmi->x.f.sca;
multp3(r->rop, rcont.rop, curmi->x.f.xfm);
multv3(r->ron, rcont.ron, curmi->x.f.xfm);
normalize(r->ron);
r->rod = -DOT(r->rdir, r->ron);
/* get triangle */
flags = getmeshtri(tv, &tmod, curmsh, rcont.robj, MT_ALL);
if (!(flags & MT_V))
objerror(o, INTERNAL, "missing mesh vertices in o_mesh");
r->robj = objndx(o); /* set object and material */
if ((o->omod == OVOID) & (tmod != OVOID)) {
r->ro = getmeshpseudo(curmsh, tmod);
r->rox = &curmi->x;
} else
r->ro = o;
/* compute barycentric weights */
if (flags & (MT_N|MT_UV))
if (get_baryc(wt, rcont.rop, tv[0].v, tv[1].v, tv[2].v) < 0) {
objerror(o, WARNING, "bad triangle in o_mesh");
flags &= ~(MT_N|MT_UV);
}
if (flags & MT_N) { /* interpolate normal */
for (i = 0; i < 3; i++)
rcont.pert[i] = wt[0]*tv[0].n[i] +
wt[1]*tv[1].n[i] +
wt[2]*tv[2].n[i];
multv3(r->pert, rcont.pert, curmi->x.f.xfm);
if (normalize(r->pert) != 0.0)
VSUB(r->pert, r->pert, r->ron);
} else
r->pert[0] = r->pert[1] = r->pert[2] = .0;
if (flags & MT_UV) /* interpolate uv coordinates */
for (i = 0; i < 2; i++)
r->uv[i] = wt[0]*tv[0].uv[i] +
wt[1]*tv[1].uv[i] +
wt[2]*tv[2].uv[i];
else
r->uv[0] = r->uv[1] = .0;
return(1); /* return hit */
}

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