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#ifndef lint
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static const char RCSid[] = "$Id: dircode.c,v 2.9 2019/05/14 17:21:50 greg Exp $";
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#endif
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/*
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* Compute a 4-byte direction code (externals defined in rtmath.h).
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*
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* Mean accuracy is 0.0022 degrees, with a maximum error of 0.0058 degrees.
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*/
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#include "rtmath.h"
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#define DCSCALE 11585.2 /* (1<<13)*sqrt(2) */
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#define FXNEG 01
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#define FYNEG 02
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#define FZNEG 04
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#define F1X 010
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#define F2Z 020
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#define F1SFT 5
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#define F2SFT 18
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#define FMASK 0x1fff
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int32
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encodedir(FVECT dv) /* encode a normalized direction vector */
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{
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int32 dc = 0;
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int cd[3], cm;
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int i;
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for (i = 0; i < 3; i++)
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if (dv[i] < 0.) {
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cd[i] = (int)(dv[i] * -DCSCALE);
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dc |= FXNEG<<i;
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} else
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cd[i] = (int)(dv[i] * DCSCALE);
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if (!(cd[0] | cd[1] | cd[2]))
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return(0); /* zero normal */
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if (cd[0] <= cd[1]) {
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dc |= F1X | cd[0] << F1SFT;
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cm = cd[1];
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} else {
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dc |= cd[1] << F1SFT;
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cm = cd[0];
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}
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if (cd[2] <= cm)
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dc |= F2Z | cd[2] << F2SFT;
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else
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dc |= cm << F2SFT;
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if (!dc) /* don't generate 0 code normally */
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dc = F1X;
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return(dc);
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}
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#if 0 /* original version for reference */
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void
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decodedir(FVECT dv, int32 dc) /* decode a normalized direction vector */
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{
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double d1, d2, der;
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if (!dc) { /* special code for zero normal */
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dv[0] = dv[1] = dv[2] = 0.;
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return;
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}
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d1 = ((dc>>F1SFT & FMASK)+.5)*(1./DCSCALE);
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d2 = ((dc>>F2SFT & FMASK)+.5)*(1./DCSCALE);
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der = sqrt(1. - d1*d1 - d2*d2);
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if (dc & F1X) {
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dv[0] = d1;
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if (dc & F2Z) { dv[1] = der; dv[2] = d2; }
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else { dv[1] = d2; dv[2] = der; }
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} else {
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dv[1] = d1;
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if (dc & F2Z) { dv[0] = der; dv[2] = d2; }
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else { dv[0] = d2; dv[2] = der; }
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}
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if (dc & FXNEG) dv[0] = -dv[0];
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if (dc & FYNEG) dv[1] = -dv[1];
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if (dc & FZNEG) dv[2] = -dv[2];
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}
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#else
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void
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decodedir(FVECT dv, int32 dc) /* decode a normalized direction vector */
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{
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static const short itab[4][3] = {
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{1,0,2},{0,1,2},{1,2,0},{0,2,1}
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};
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static const RREAL neg[2] = {1., -1.};
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const int ndx = ((dc & F2Z) != 0)<<1 | ((dc & F1X) != 0);
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double d1, d2, der;
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if (!dc) { /* special code for zero normal */
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dv[0] = dv[1] = dv[2] = 0.;
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return;
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}
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d1 = ((dc>>F1SFT & FMASK)+.5)*(1./DCSCALE);
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d2 = ((dc>>F2SFT & FMASK)+.5)*(1./DCSCALE);
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der = sqrt(1. - d1*d1 - d2*d2);
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dv[itab[ndx][0]] = d1;
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dv[itab[ndx][1]] = d2;
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dv[itab[ndx][2]] = der;
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dv[0] *= neg[(dc&FXNEG)!=0];
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dv[1] *= neg[(dc&FYNEG)!=0];
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dv[2] *= neg[(dc&FZNEG)!=0];
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}
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#endif
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double
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dir2diff(int32 dc1, int32 dc2) /* approx. radians^2 between directions */
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{
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FVECT v1, v2;
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if (dc1 == dc2)
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return 0.;
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decodedir(v1, dc1);
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decodedir(v2, dc2);
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return(2. - 2.*DOT(v1,v2));
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}
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double
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fdir2diff(int32 dc1, FVECT v2) /* approx. radians^2 between directions */
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{
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FVECT v1;
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decodedir(v1, dc1);
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return(2. - 2.*DOT(v1,v2));
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}
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