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#ifndef lint |
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static const char RCSid[] = "$Id: o_face.c,v 2.3 2003/07/27 22:12:03 schorsch Exp $"; |
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#endif |
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/* |
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* o_face.c - routines for creating octrees for polygonal faces. |
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* |
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* 8/27/85 |
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*/ |
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|
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#include "standard.h" |
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|
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#include "octree.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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#include "plocate.h" |
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|
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/* |
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* The algorithm for determining a face's intersection |
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* with a cube is relatively straightforward: |
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* |
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* 1) Check to see if any vertices are inside the cube |
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* (intersection). |
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* |
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* 2) Check to see if all vertices are to one side of |
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* cube (no intersection). |
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* |
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* 3) Check to see if any portion of any edge is inside |
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* cube (intersection). |
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* |
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* 4) Check to see if the cube cuts the plane of the |
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* face and one of its edges passes through |
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* the face (intersection). |
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* |
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* 5) If test 4 fails, we have no intersection. |
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*/ |
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|
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/* XXX this is extern, but not declared in any header file yet */ |
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int |
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o_face( /* determine if face intersects cube */ |
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OBJREC *o, |
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CUBE *cu |
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) |
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{ |
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FVECT cumin, cumax; |
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FVECT v1, v2; |
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double d1, d2; |
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int vloc; |
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register FACE *f; |
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register int i, j; |
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/* get face arguments */ |
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f = getface(o); |
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if (f->area == 0.0) /* empty face */ |
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return(O_MISS); |
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/* compute cube boundaries */ |
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for (j = 0; j < 3; j++) |
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cumax[j] = (cumin[j] = cu->cuorg[j]-FTINY) |
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+ cu->cusize + 2.0*FTINY; |
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|
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vloc = ABOVE | BELOW; /* check vertices */ |
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for (i = 0; i < f->nv; i++) |
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if ( (j = plocate(VERTEX(f,i), cumin, cumax)) ) |
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vloc &= j; |
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else |
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return(O_HIT); /* vertex inside */ |
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|
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if (vloc) /* all to one side */ |
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return(O_MISS); |
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|
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for (i = 0; i < f->nv; i++) { /* check edges */ |
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if ((j = i + 1) >= f->nv) |
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j = 0; /* wrap around */ |
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VCOPY(v1, VERTEX(f,i)); /* clip modifies */ |
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VCOPY(v2, VERTEX(f,j)); /* the vertices! */ |
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if (clip(v1, v2, cumin, cumax)) |
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return(O_HIT); /* edge inside */ |
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} |
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/* see if cube cuts plane */ |
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for (j = 0; j < 3; j++) |
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if (f->norm[j] > 0.0) { |
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v1[j] = cumin[j]; |
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v2[j] = cumax[j]; |
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} else { |
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v1[j] = cumax[j]; |
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v2[j] = cumin[j]; |
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} |
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if ((d1 = DOT(v1, f->norm) - f->offset) > FTINY) |
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return(O_MISS); |
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if ((d2 = DOT(v2, f->norm) - f->offset) < -FTINY) |
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return(O_MISS); |
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/* intersect face */ |
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for (j = 0; j < 3; j++) |
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v1[j] = (v1[j]*d2 - v2[j]*d1)/(d2 - d1); |
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if (inface(v1, f)) |
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return(O_HIT); |
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|
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return(O_MISS); /* no intersection */ |
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} |
