This is meshnormal.c in view mode; [Download] [Up]
/* Copyright (c) 1992 The Geometry Center; University of Minnesota
1300 South Second Street; Minneapolis, MN 55454, USA;
This file is part of geomview/OOGL. geomview/OOGL is free software;
you can redistribute it and/or modify it only under the terms given in
the file COPYING, which you should have received along with this file.
This and other related software may be obtained via anonymous ftp from
geom.umn.edu; email: software@geom.umn.edu. */
/* Authors: Charlie Gunn, Stuart Levy, Tamara Munzner, Mark Phillips */
#include "meshP.h"
static void mnorm();
Mesh *
MeshComputeNormals(Mesh *m)
{
register HPoint3 *normp = NULL, *normptr, *pptr;
int i;
if(m->n) {
GeomFree(m->n);
}
m->n = GeomNewN(Point3, m->nu * m->nv);
m->flag |= MESH_N;
/* if this a '4D' mesh, we need to dehomogenize (temporarily)
before computing the normals */
if (m->geomflags & VERT_4D) {
normp = GeomNewN(HPoint3, m->nu * m->nv);
for (normptr = normp, pptr = m->p, i=0;
i < m->nu * m->nv;
++i, ++pptr, ++normptr)
HPt3Normalize(pptr, normptr);
}
mnorm(m->geomflags & VERT_4D ? normp : m->p, m->n, m->nu, m->nv,
m->flag & MESH_UWRAP, m->flag & MESH_VWRAP, m->flag & MESH_EVERT);
if (m->geomflags & VERT_4D) GeomFree(normp);
return m;
}
static void
mnorm(ap, an, nu, nv, uwrap, vwrap, evert)
HPoint3 *ap;
Point3 *an;
int nu, nv;
int uwrap, vwrap;
int evert;
{
register HPoint3 *prev, *next;
register Point3 *n;
register int k;
int u, v;
float x,y,z, norm;
float unit;
/*
* We set the normal at each point to be the mean of the
* cross products at the four adjacent points. I.e.:
* n Given mesh point p and its four orthogonal neighbors
* w p e e, n, w, s we define displacements E=e-p, N=n-p, ...
* s and compute normal(p) = ExN + NxW + WxS + SxE
* This turns out to be equal to (e-w) x (n-s) -- independent of p!
*
* Since the index arithmetic gets a bit messy at the boundaries
* we make two passes. Pass 1 computes e-w and holds it in
* the array to be filled with normals.
* Pass 2 computes n-s, takes the cross product and normalizes.
*/
unit = evert ? -1.0 : 1.0;
for(u = 0; u < nu; u++) {
if(u == 0) {
prev = &ap[uwrap ? nu-1 : 0];
next = &ap[u+1];
} else if(u == nu-1) {
prev = &ap[u-1];
next = &ap[uwrap ? 0 : u];
} else {
prev = &ap[u-1];
next = &ap[u+1];
}
n = &an[u];
k = nv;
do {
n->x = next->x - prev->x; /* e - w */
n->y = next->y - prev->y;
n->z = next->z - prev->z;
n += nu; /* advance to next v row */
prev += nu;
next += nu;
} while(--k > 0);
}
for(v = 0; v < nv; v++) {
if(v == 0) {
prev = &ap[vwrap ? nu*(nv-1) : 0];
next = &ap[nu*1];
} else if(v == nv-1) {
prev = &ap[nu*(v-1)];
next = &ap[vwrap ? 0 : nu*v];
} else {
prev = &ap[nu*(v-1)];
next = &ap[nu*(v+1)];
}
n = &an[nu*v];
k = nu;
do {
Point3 t;
t.x = next->x - prev->x;
t.y = next->y - prev->y;
t.z = next->z - prev->z;
x = n->y * t.z - n->z * t.y;
y = n->z * t.x - n->x * t.z;
z = n->x * t.y - n->y * t.x;
norm = x*x + y*y + z*z;
if(norm == 0.0) {
/*
* Oh no, degenerate norm.
* Let's hope it happened because (part of) a row of
* mesh points coincided -- maybe even though N=S,
* NE != SE or NW != SW.
*/
if(t.x == 0.0 && t.y == 0.0 && t.z == 0.0) {
if(k > 1) {
t.x = (next+1)->x - (prev+1)->x;
t.y = (next+1)->y - (prev+1)->y;
t.z = (next+1)->z - (prev+1)->z;
}
if(t.x == 0.0 && t.y == 0.0 && t.z == 0.0 && k < nu) {
t.x = (next-1)->x - (prev-1)->x;
t.y = (next-1)->y - (prev-1)->y;
t.z = (next-1)->z - (prev-1)->z;
}
}
if(n->x == 0.0 && n->y == 0.0 && n->z == 0.0) {
/* Do likewise in E-W direction. */
register HPoint3 *cur = &ap[nu*(v+1) - k];
if(k == 1) cur--;
else if(k == nu) cur++;
if(v > 0) {
cur -= nu; /* SE-SW */
n->x = (cur+1)->x - (cur-1)->x;
n->y = (cur+1)->y - (cur-1)->y;
n->z = (cur+1)->z - (cur-1)->z;
}
if(n->x==0.0 && n->y==0.0 && n->z==0.0 && v < nv-1) {
cur += 2*nu; /* NE-NW */
n->x = (cur+1)->x - (cur-1)->x;
n->y = (cur+1)->y - (cur-1)->y;
n->z = (cur+1)->z - (cur-1)->z;
}
}
x = n->y * t.z - n->z * t.y;
y = n->z * t.x - n->x * t.z;
z = n->x * t.y - n->y * t.x;
norm = x*x + y*y + z*z;
if(norm == 0.0) {
/* Oh well. */
n->x = unit;
norm = 1.0;
}
}
norm = unit / sqrt(norm);
n->x = x*norm;
n->y = y*norm;
n->z = z*norm;
n++; /* Next u column */
prev++;
next++;
} while(--k > 0);
}
}
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