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#ifndef lint |
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static const char RCSid[] = "$Id$"; |
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#endif |
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/* |
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* clip.c - routine to clip 3D line segments to a box. |
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*/ |
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|
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#include "copyright.h" |
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|
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#include "fvect.h" |
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|
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#include "plocate.h" |
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|
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#define MAXITER 6 /* maximum possible number of iterations */ |
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|
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|
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int |
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clip(ep1, ep2, min, max) /* clip a line segment to a box */ |
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FLOAT *ep1, *ep2; |
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FVECT min, max; |
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{ |
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int itlim = MAXITER; |
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int loc1, loc2; |
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int accept; |
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FLOAT *dp; |
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double d; |
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register int i, j; |
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|
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/* |
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* The Cohen-Sutherland algorithm is used to determine |
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* what part (if any) of the given line segment is contained |
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* in the box specified by the min and max vectors. |
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* The routine returns non-zero if any segment is left. |
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*/ |
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|
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loc1 = plocate(ep1, min, max); |
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loc2 = plocate(ep2, min, max); |
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|
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/* check for trivial accept and reject */ |
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/* trivial accept is both points inside */ |
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/* trivial reject is both points to one side */ |
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|
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while (!((accept = !(loc1 | loc2)) || (loc1 & loc2))) { |
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|
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if (itlim-- <= 0) /* past theoretical limit? */ |
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return(0); /* quit fooling around */ |
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|
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if (!loc1) { /* make sure first point is outside */ |
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dp = ep1; ep1 = ep2; ep2 = dp; |
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i = loc1; loc1 = loc2; loc2 = i; |
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} |
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|
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for (i = 0; i < 3; i++) { /* chop segment */ |
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|
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if (loc1 & position(i) & BELOW) { |
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d = (min[i] - ep1[i])/(ep2[i] - ep1[i]); |
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ep1[i] = min[i]; |
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} else if (loc1 & position(i) & ABOVE) { |
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d = (max[i] - ep1[i])/(ep2[i] - ep1[i]); |
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ep1[i] = max[i]; |
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} else |
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continue; |
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|
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for (j = 0; j < 3; j++) |
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if (j != i) |
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ep1[j] += (ep2[j] - ep1[j])*d; |
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break; |
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} |
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loc1 = plocate(ep1, min, max); |
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} |
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return(accept); |
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} |
