src/common/face.c

#ifndef lint
static const char RCSid[] = "$Id$";
#endif
/*
 *  face.c - routines dealing with polygonal faces.
 */

#include "copyright.h"

#include  "standard.h"

#include  "object.h"

#include  "face.h"

/*
 *      A face is given as a list of 3D vertices.  The normal
 *  direction and therefore the surface orientation is determined
 *  by the ordering of the vertices.  Looking in the direction opposite
 *  the normal (at the front of the face), the vertices will be
 *  listed in counter-clockwise order.
 *      There is no checking done to insure that the edges do not cross
 *  one another.  This was considered too expensive and should be unnecessary.
 *  The last vertex is automatically connected to the first.
 */

#ifdef  SMLFLT
#define  VERTEPS        1e-2            /* allowed vertex error */
#else
#define  VERTEPS        1e-4            /* allowed vertex error */
#endif


FACE *
getface(o)                      /* get arguments for a face */
OBJREC  *o;
{
        double  d1;
        int  badvert;
        FVECT  v1, v2, v3;
        register FACE  *f;
        register int  i;

        if ((f = (FACE *)o->os) != NULL)
                return(f);                      /* already done */

        f = (FACE *)malloc(sizeof(FACE));
        if (f == NULL)
                error(SYSTEM, "out of memory in makeface");

        if (o->oargs.nfargs < 9 || o->oargs.nfargs % 3)
                objerror(o, USER, "bad # arguments");

        o->os = (char *)f;                      /* save face */

        f->va = o->oargs.farg;
        f->nv = o->oargs.nfargs / 3;
                                                /* check for last==first */
        if (dist2(VERTEX(f,0),VERTEX(f,f->nv-1)) <= FTINY*FTINY)
                f->nv--;
                                                /* compute area and normal */
        f->norm[0] = f->norm[1] = f->norm[2] = 0.0;
        v1[0] = VERTEX(f,1)[0] - VERTEX(f,0)[0];
        v1[1] = VERTEX(f,1)[1] - VERTEX(f,0)[1];
        v1[2] = VERTEX(f,1)[2] - VERTEX(f,0)[2];
        for (i = 2; i < f->nv; i++) {
                v2[0] = VERTEX(f,i)[0] - VERTEX(f,0)[0];
                v2[1] = VERTEX(f,i)[1] - VERTEX(f,0)[1];
                v2[2] = VERTEX(f,i)[2] - VERTEX(f,0)[2];
                fcross(v3, v1, v2);
                f->norm[0] += v3[0];
                f->norm[1] += v3[1];
                f->norm[2] += v3[2];
                VCOPY(v1, v2);
        }
        f->area = normalize(f->norm);
        if (f->area == 0.0) {
                objerror(o, WARNING, "zero area");      /* used to be fatal */
                f->offset = 0.0;
                f->ax = 0;
                return(f);
        }
        f->area *= 0.5;
                                                /* compute offset */
        badvert = 0;
        f->offset = DOT(f->norm, VERTEX(f,0));
        for (i = 1; i < f->nv; i++) {
                d1 = DOT(f->norm, VERTEX(f,i));
                badvert += fabs(d1 - f->offset/i) > VERTEPS;
                f->offset += d1;
        }
        f->offset /= (double)f->nv;
        if (badvert)
                objerror(o, WARNING, "non-planar vertex");
                                                /* find axis */
        f->ax = fabs(f->norm[0]) > fabs(f->norm[1]) ? 0 : 1;
        if (fabs(f->norm[2]) > fabs(f->norm[f->ax]))
                f->ax = 2;

        return(f);
}


void
freeface(o)                     /* free memory associated with face */
OBJREC  *o;
{
        if (o->os == NULL)
                return;
        free(o->os);
        o->os = NULL;
}


int
inface(p, f)                    /* determine if point is in face */
FVECT  p;
FACE  *f;
{
        int  ncross, n;
        double  x, y;
        int  tst;
        register int  xi, yi;
        register FLOAT  *p0, *p1;

        xi = (f->ax+1)%3;
        yi = (f->ax+2)%3;
        x = p[xi];
        y = p[yi];
        n = f->nv;
        p0 = f->va + 3*(n-1);           /* connect last to first */
        p1 = f->va;
        ncross = 0;
                                        /* positive x axis cross test */
        while (n--) {
                if ((p0[yi] > y) ^ (p1[yi] > y)) {
                        tst = (p0[xi] > x) + (p1[xi] > x);
                        if (tst == 2)
                                ncross++;
                        else if (tst)
                                ncross += (p1[yi] > p0[yi]) ^
                                                ((p0[yi]-y)*(p1[xi]-x) >
                                                (p0[xi]-x)*(p1[yi]-y));
                }
                p0 = p1;
                p1 += 3;
        }
        return(ncross & 01);
}
Revision:	2.8
Committed:	Wed Mar 12 17:26:58 2003 UTC (22 years, 7 months ago) by greg
Content type:	text/plain
Branch:	MAIN
Changes since 2.7:	+7 -4 lines
Log Message:	Returned old behavior with flat surfaces and improved documentation
#	User	Rev	Content
1	greg	1.1	#ifndef lint
2	greg	2.8	static const char RCSid[] = "$Id$";
3	greg	1.1	#endif
4			/*
5			* face.c - routines dealing with polygonal faces.
6	greg	2.6	*/
7
8	greg	2.7	#include "copyright.h"
9	greg	1.1
10			#include "standard.h"
11
12			#include "object.h"
13
14			#include "face.h"
15
16			/*
17			* A face is given as a list of 3D vertices. The normal
18			* direction and therefore the surface orientation is determined
19			* by the ordering of the vertices. Looking in the direction opposite
20			* the normal (at the front of the face), the vertices will be
21			* listed in counter-clockwise order.
22			* There is no checking done to insure that the edges do not cross
23			* one another. This was considered too expensive and should be unnecessary.
24			* The last vertex is automatically connected to the first.
25			*/
26
27	greg	2.3	#ifdef SMLFLT
28			#define VERTEPS 1e-2 /* allowed vertex error */
29			#else
30	greg	1.1	#define VERTEPS 1e-4 /* allowed vertex error */
31	greg	2.3	#endif
32	greg	1.1
33
34			FACE *
35			getface(o) /* get arguments for a face */
36			OBJREC *o;
37			{
38			double d1;
39			int badvert;
40			FVECT v1, v2, v3;
41			register FACE *f;
42			register int i;
43
44			if ((f = (FACE *)o->os) != NULL)
45			return(f); /* already done */
46
47			f = (FACE *)malloc(sizeof(FACE));
48			if (f == NULL)
49			error(SYSTEM, "out of memory in makeface");
50
51			if (o->oargs.nfargs < 9 \|\| o->oargs.nfargs % 3)
52			objerror(o, USER, "bad # arguments");
53
54	greg	1.3	o->os = (char )f; / save face */
55
56	greg	1.1	f->va = o->oargs.farg;
57			f->nv = o->oargs.nfargs / 3;
58	greg	2.4	/* check for last==first */
59			if (dist2(VERTEX(f,0),VERTEX(f,f->nv-1)) <= FTINY*FTINY)
60			f->nv--;
61	greg	1.1	/* compute area and normal */
62			f->norm[0] = f->norm[1] = f->norm[2] = 0.0;
63	greg	2.5	v1[0] = VERTEX(f,1)[0] - VERTEX(f,0)[0];
64			v1[1] = VERTEX(f,1)[1] - VERTEX(f,0)[1];
65			v1[2] = VERTEX(f,1)[2] - VERTEX(f,0)[2];
66			for (i = 2; i < f->nv; i++) {
67	greg	1.1	v2[0] = VERTEX(f,i)[0] - VERTEX(f,0)[0];
68			v2[1] = VERTEX(f,i)[1] - VERTEX(f,0)[1];
69			v2[2] = VERTEX(f,i)[2] - VERTEX(f,0)[2];
70			fcross(v3, v1, v2);
71			f->norm[0] += v3[0];
72			f->norm[1] += v3[1];
73			f->norm[2] += v3[2];
74			VCOPY(v1, v2);
75			}
76			f->area = normalize(f->norm);
77			if (f->area == 0.0) {
78			objerror(o, WARNING, "zero area"); /* used to be fatal */
79	greg	1.2	f->offset = 0.0;
80	greg	1.1	f->ax = 0;
81			return(f);
82			}
83			f->area *= 0.5;
84	greg	1.2	/* compute offset */
85	greg	1.1	badvert = 0;
86	greg	1.2	f->offset = DOT(f->norm, VERTEX(f,0));
87	greg	1.1	for (i = 1; i < f->nv; i++) {
88			d1 = DOT(f->norm, VERTEX(f,i));
89	greg	1.2	badvert += fabs(d1 - f->offset/i) > VERTEPS;
90			f->offset += d1;
91	greg	1.1	}
92	greg	1.5	f->offset /= (double)f->nv;
93	greg	1.1	if (badvert)
94			objerror(o, WARNING, "non-planar vertex");
95			/* find axis */
96			f->ax = fabs(f->norm[0]) > fabs(f->norm[1]) ? 0 : 1;
97			if (fabs(f->norm[2]) > fabs(f->norm[f->ax]))
98			f->ax = 2;
99
100			return(f);
101			}
102
103
104	greg	2.6	void
105	greg	1.1	freeface(o) /* free memory associated with face */
106			OBJREC *o;
107			{
108	greg	1.4	if (o->os == NULL)
109			return;
110	greg	1.1	free(o->os);
111			o->os = NULL;
112			}
113
114
115	greg	2.6	int
116	greg	1.1	inface(p, f) /* determine if point is in face */
117			FVECT p;
118			FACE *f;
119			{
120			int ncross, n;
121			double x, y;
122	greg	2.8	int tst;
123	greg	1.1	register int xi, yi;
124	greg	1.6	register FLOAT p0, p1;
125	greg	1.1
126			xi = (f->ax+1)%3;
127			yi = (f->ax+2)%3;
128			x = p[xi];
129			y = p[yi];
130			n = f->nv;
131			p0 = f->va + 3(n-1); / connect last to first */
132			p1 = f->va;
133			ncross = 0;
134			/* positive x axis cross test */
135			while (n--) {
136	greg	2.8	if ((p0[yi] > y) ^ (p1[yi] > y)) {
137			tst = (p0[xi] > x) + (p1[xi] > x);
138			if (tst == 2)
139	greg	1.1	ncross++;
140	greg	2.8	else if (tst)
141	greg	1.1	ncross += (p1[yi] > p0[yi]) ^
142			((p0[yi]-y)*(p1[xi]-x) >
143			(p0[xi]-x)*(p1[yi]-y));
144	greg	2.8	}
145	greg	1.1	p0 = p1;
146			p1 += 3;
147			}
148			return(ncross & 01);
149			}