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#ifndef lint |
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static const char RCSid[] = "$Id: face.c,v 2.17 2024/08/18 00:06:10 greg Exp $"; |
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#endif |
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/* |
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* face.c - routines dealing with polygonal faces. |
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*/ |
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|
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#include "copyright.h" |
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|
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#include "standard.h" |
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|
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#include "object.h" |
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|
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#include "face.h" |
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|
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/* |
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* A face is given as a list of 3D vertices. The normal |
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* direction and therefore the surface orientation is determined |
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* by the ordering of the vertices. Looking in the direction opposite |
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* the normal (at the front of the face), the vertices will be |
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* listed in counter-clockwise order. |
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* There is no checking done to insure that the edges do not cross |
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* one another. This was considered too expensive and should be unnecessary. |
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* The last vertex is automatically connected to the first. |
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*/ |
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|
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#ifdef SMLFLT |
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#define VERTEPS 1e-3 /* allowed vertex error */ |
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#else |
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#define VERTEPS 1e-5 /* allowed vertex error */ |
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#endif |
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|
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|
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FACE * |
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getface( /* get arguments for a face */ |
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OBJREC *o |
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) |
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{ |
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double d1; |
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int smalloff, badvert; |
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FVECT v1, v2, v3; |
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FACE *f; |
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int i; |
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|
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if ((f = (FACE *)o->os) != NULL) |
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return(f); /* already done */ |
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|
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f = (FACE *)malloc(sizeof(FACE)); |
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if (f == NULL) |
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error(SYSTEM, "out of memory in makeface"); |
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|
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if (o->oargs.nfargs < 9 || o->oargs.nfargs % 3) |
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objerror(o, USER, "bad # arguments"); |
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|
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o->os = (char *)f; /* save face */ |
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|
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f->va = o->oargs.farg; |
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f->nv = o->oargs.nfargs / 3; |
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/* check for last==first */ |
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if (f->nv > 3 && dist2(VERTEX(f,0),VERTEX(f,f->nv-1)) <= FTINY*FTINY) |
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f->nv--; |
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/* compute area and normal */ |
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f->norm[0] = f->norm[1] = f->norm[2] = 0.0; |
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v1[0] = VERTEX(f,1)[0] - VERTEX(f,0)[0]; |
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v1[1] = VERTEX(f,1)[1] - VERTEX(f,0)[1]; |
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v1[2] = VERTEX(f,1)[2] - VERTEX(f,0)[2]; |
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for (i = 2; i < f->nv; i++) { |
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v2[0] = VERTEX(f,i)[0] - VERTEX(f,0)[0]; |
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v2[1] = VERTEX(f,i)[1] - VERTEX(f,0)[1]; |
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v2[2] = VERTEX(f,i)[2] - VERTEX(f,0)[2]; |
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fcross(v3, v1, v2); |
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f->norm[0] += v3[0]; |
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f->norm[1] += v3[1]; |
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f->norm[2] += v3[2]; |
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VCOPY(v1, v2); |
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} |
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f->area = normalize(f->norm); |
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if (f->area == 0.0) { |
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objerror(o, WARNING, "zero area"); /* used to be fatal */ |
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f->offset = 0.0; |
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f->ax = 0; |
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return(f); |
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} |
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f->area *= 0.5; |
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/* compute offset */ |
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badvert = 0; |
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f->offset = DOT(f->norm, VERTEX(f,0)); |
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smalloff = fabs(f->offset) <= VERTEPS; |
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for (i = 1; i < f->nv; i++) { |
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d1 = DOT(f->norm, VERTEX(f,i)); |
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if (smalloff) |
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badvert += fabs(d1 - f->offset/i) > VERTEPS; |
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else |
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badvert += fabs(1.0 - d1*i/f->offset) > VERTEPS; |
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f->offset += d1; |
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} |
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f->offset /= (double)f->nv; |
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if (f->nv > 3 && badvert) |
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objerror(o, WARNING, "non-planar vertex"); |
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/* find axis */ |
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f->ax = (fabs(f->norm[1]) > fabs(f->norm[0])); |
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if (fabs(f->norm[2]) > fabs(f->norm[f->ax])) |
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f->ax = 2; |
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|
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return(f); |
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} |
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|
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|
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void |
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freeface( /* free memory associated with face */ |
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OBJREC *o |
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) |
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{ |
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if (o->os == NULL) |
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return; |
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free(o->os); |
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o->os = NULL; |
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} |
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|
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int |
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inface( /* determine if point is in face */ |
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FVECT p, |
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FACE *f |
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) |
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{ |
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int ncross, n; |
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double x, y; |
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int tst; |
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int xi, yi; |
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RREAL *p0, *p1; |
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|
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if ((xi = f->ax + 1) >= 3) xi -= 3; |
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if ((yi = xi + 1) >= 3) yi -= 3; |
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x = p[xi]; |
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y = p[yi]; |
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n = f->nv; |
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p0 = f->va + 3*(n-1); /* connect last to first */ |
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p1 = f->va; |
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ncross = 0; |
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/* positive x axis cross test */ |
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while (n--) { |
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if (FABSEQ(p0[yi], y) && FABSEQ(p1[yi], y) && |
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(p0[xi] > x) ^ (p1[xi] > x)) |
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return(1); /* edge case #1 */ |
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if ((p0[yi] > y) ^ (p1[yi] > y)) { |
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tst = (p0[xi] > x) + (p1[xi] > x); |
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if (tst == 2) |
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ncross++; |
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else if (tst) { |
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double prodA = (p0[yi]-y)*(p1[xi]-x); |
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double prodB = (p0[xi]-x)*(p1[yi]-y); |
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if (FABSEQ(prodA, prodB)) |
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return(1); /* edge case #2 */ |
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ncross += (p1[yi] > p0[yi]) ^ (prodA > prodB); |
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} else if (FABSEQ(p0[xi], x) && FABSEQ(p1[xi], x)) |
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return(1); /* edge case #3 */ |
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} |
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p0 = p1; |
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p1 += 3; |
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} |
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return(ncross & 01); |
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} |
