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#ifndef lint |
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static const char RCSid[] = "$Id: dircode.c,v 2.12 2020/03/06 19:05:19 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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|
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#include "rtmath.h" |
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|
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#define DCSCALE 11584.5 /* ((1<<13)-.5)*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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|
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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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|
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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 + .5); |
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dc |= FXNEG<<i; |
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} else |
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cd[i] = (int)(dv[i] * DCSCALE + .5); |
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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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|
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#if 0 /* original version for reference */ |
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|
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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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|
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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)*(1./DCSCALE); |
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d2 = (dc>>F2SFT & FMASK)*(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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|
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#else |
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|
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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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|
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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)*(1./DCSCALE); |
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d2 = (dc>>F2SFT & FMASK)*(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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|
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#endif |
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|
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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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|
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if (dc1 == dc2) |
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return 0.; |
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|
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decodedir(v1, dc1); |
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decodedir(v2, dc2); |
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|
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return(2. - 2.*DOT(v1,v2)); |
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} |
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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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|
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decodedir(v1, dc1); |
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|
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return(2. - 2.*DOT(v1,v2)); |
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} |
