1 |
#ifndef lint |
2 |
static const char RCSid[] = "$Id: dircode.c,v 2.9 2019/05/14 17:21:50 greg Exp $"; |
3 |
#endif |
4 |
/* |
5 |
* Compute a 4-byte direction code (externals defined in rtmath.h). |
6 |
* |
7 |
* Mean accuracy is 0.0022 degrees, with a maximum error of 0.0058 degrees. |
8 |
*/ |
9 |
|
10 |
#include "rtmath.h" |
11 |
|
12 |
#define DCSCALE 11585.2 /* (1<<13)*sqrt(2) */ |
13 |
#define FXNEG 01 |
14 |
#define FYNEG 02 |
15 |
#define FZNEG 04 |
16 |
#define F1X 010 |
17 |
#define F2Z 020 |
18 |
#define F1SFT 5 |
19 |
#define F2SFT 18 |
20 |
#define FMASK 0x1fff |
21 |
|
22 |
int32 |
23 |
encodedir(FVECT dv) /* encode a normalized direction vector */ |
24 |
{ |
25 |
int32 dc = 0; |
26 |
int cd[3], cm; |
27 |
int i; |
28 |
|
29 |
for (i = 0; i < 3; i++) |
30 |
if (dv[i] < 0.) { |
31 |
cd[i] = (int)(dv[i] * -DCSCALE); |
32 |
dc |= FXNEG<<i; |
33 |
} else |
34 |
cd[i] = (int)(dv[i] * DCSCALE); |
35 |
if (!(cd[0] | cd[1] | cd[2])) |
36 |
return(0); /* zero normal */ |
37 |
if (cd[0] <= cd[1]) { |
38 |
dc |= F1X | cd[0] << F1SFT; |
39 |
cm = cd[1]; |
40 |
} else { |
41 |
dc |= cd[1] << F1SFT; |
42 |
cm = cd[0]; |
43 |
} |
44 |
if (cd[2] <= cm) |
45 |
dc |= F2Z | cd[2] << F2SFT; |
46 |
else |
47 |
dc |= cm << F2SFT; |
48 |
if (!dc) /* don't generate 0 code normally */ |
49 |
dc = F1X; |
50 |
return(dc); |
51 |
} |
52 |
|
53 |
#if 0 /* original version for reference */ |
54 |
|
55 |
void |
56 |
decodedir(FVECT dv, int32 dc) /* decode a normalized direction vector */ |
57 |
{ |
58 |
double d1, d2, der; |
59 |
|
60 |
if (!dc) { /* special code for zero normal */ |
61 |
dv[0] = dv[1] = dv[2] = 0.; |
62 |
return; |
63 |
} |
64 |
d1 = ((dc>>F1SFT & FMASK)+.5)*(1./DCSCALE); |
65 |
d2 = ((dc>>F2SFT & FMASK)+.5)*(1./DCSCALE); |
66 |
der = sqrt(1. - d1*d1 - d2*d2); |
67 |
if (dc & F1X) { |
68 |
dv[0] = d1; |
69 |
if (dc & F2Z) { dv[1] = der; dv[2] = d2; } |
70 |
else { dv[1] = d2; dv[2] = der; } |
71 |
} else { |
72 |
dv[1] = d1; |
73 |
if (dc & F2Z) { dv[0] = der; dv[2] = d2; } |
74 |
else { dv[0] = d2; dv[2] = der; } |
75 |
} |
76 |
if (dc & FXNEG) dv[0] = -dv[0]; |
77 |
if (dc & FYNEG) dv[1] = -dv[1]; |
78 |
if (dc & FZNEG) dv[2] = -dv[2]; |
79 |
} |
80 |
|
81 |
#else |
82 |
|
83 |
void |
84 |
decodedir(FVECT dv, int32 dc) /* decode a normalized direction vector */ |
85 |
{ |
86 |
static const short itab[4][3] = { |
87 |
{1,0,2},{0,1,2},{1,2,0},{0,2,1} |
88 |
}; |
89 |
static const RREAL neg[2] = {1., -1.}; |
90 |
const int ndx = ((dc & F2Z) != 0)<<1 | ((dc & F1X) != 0); |
91 |
double d1, d2, der; |
92 |
|
93 |
if (!dc) { /* special code for zero normal */ |
94 |
dv[0] = dv[1] = dv[2] = 0.; |
95 |
return; |
96 |
} |
97 |
d1 = ((dc>>F1SFT & FMASK)+.5)*(1./DCSCALE); |
98 |
d2 = ((dc>>F2SFT & FMASK)+.5)*(1./DCSCALE); |
99 |
der = sqrt(1. - d1*d1 - d2*d2); |
100 |
dv[itab[ndx][0]] = d1; |
101 |
dv[itab[ndx][1]] = d2; |
102 |
dv[itab[ndx][2]] = der; |
103 |
dv[0] *= neg[(dc&FXNEG)!=0]; |
104 |
dv[1] *= neg[(dc&FYNEG)!=0]; |
105 |
dv[2] *= neg[(dc&FZNEG)!=0]; |
106 |
} |
107 |
|
108 |
#endif |
109 |
|
110 |
double |
111 |
dir2diff(int32 dc1, int32 dc2) /* approx. radians^2 between directions */ |
112 |
{ |
113 |
FVECT v1, v2; |
114 |
|
115 |
if (dc1 == dc2) |
116 |
return 0.; |
117 |
|
118 |
decodedir(v1, dc1); |
119 |
decodedir(v2, dc2); |
120 |
|
121 |
return(2. - 2.*DOT(v1,v2)); |
122 |
} |
123 |
|
124 |
double |
125 |
fdir2diff(int32 dc1, FVECT v2) /* approx. radians^2 between directions */ |
126 |
{ |
127 |
FVECT v1; |
128 |
|
129 |
decodedir(v1, dc1); |
130 |
|
131 |
return(2. - 2.*DOT(v1,v2)); |
132 |
} |