Commit | Line | Data |
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af58ef32 SC |
1 | #include <stdio.h> |
2 | #include <math.h> | |
3 | #include <malloc.h> | |
4 | ||
5 | /* | |
6 | * adapted from Paul Heckbert's algorithm on p 657-659 of | |
7 | * Andrew S. Glassner's book, "Graphics Gems" | |
8 | * ISBN 0-12-286166-3 | |
9 | * | |
10 | */ | |
11 | ||
12 | #include "tickmarks.h" | |
13 | ||
14 | #define MAX(a, b) (((a) < (b)) ? (b) : (a)) | |
15 | ||
16 | static double nicenum(double x, int round) | |
17 | { | |
18 | int exp; /* exponent of x */ | |
19 | double f; /* fractional part of x */ | |
20 | ||
21 | exp = floor(log10(x)); | |
22 | f = x / pow(10.0, exp); | |
23 | if (round) { | |
24 | if (f < 1.5) | |
25 | return 1.0 * pow(10.0, exp); | |
26 | if (f < 3.0) | |
27 | return 2.0 * pow(10.0, exp); | |
28 | if (f < 7.0) | |
29 | return 5.0 * pow(10.0, exp); | |
30 | return 10.0 * pow(10.0, exp); | |
31 | } | |
32 | if (f <= 1.0) | |
33 | return 1.0 * pow(10.0, exp); | |
34 | if (f <= 2.0) | |
35 | return 2.0 * pow(10.0, exp); | |
36 | if (f <= 5.0) | |
37 | return 5.0 * pow(10.0, exp); | |
38 | return 10.0 * pow(10.0, exp); | |
39 | } | |
40 | ||
41 | int calc_tickmarks(double min, double max, int nticks, struct tickmark **tm) | |
42 | { | |
43 | char str[100]; | |
44 | int nfrac; | |
45 | double d; /* tick mark spacing */ | |
46 | double graphmin, graphmax; /* graph range min and max */ | |
47 | double range, x; | |
48 | int count, i; | |
49 | ||
50 | /* we expect min != max */ | |
51 | range = nicenum(max - min, 0); | |
52 | d = nicenum(range / (nticks - 1), 1); | |
53 | graphmin = floor(min / d) * d; | |
54 | graphmax = ceil(max / d) * d; | |
55 | nfrac = MAX(-floor(log10(d)), 0); | |
56 | snprintf(str, sizeof(str)-1, "%%.%df", nfrac); | |
57 | ||
58 | count = ((graphmax + 0.5 * d) - graphmin) / d + 1; | |
59 | *tm = malloc(sizeof(**tm) * count); | |
60 | ||
61 | i = 0; | |
62 | for (x = graphmin; x < graphmax + 0.5 * d; x += d) { | |
63 | (*tm)[i].value = x; | |
64 | sprintf((*tm)[i].string, str, x); | |
65 | i++; | |
66 | } | |
67 | return i; | |
68 | } | |
69 | ||
70 | #if 0 | |
71 | ||
72 | static void test_range(double x, double y) | |
73 | { | |
74 | int nticks, i; | |
75 | ||
76 | struct tickmark *tm = NULL; | |
77 | printf("Testing range %g - %g\n", x, y); | |
78 | nticks = calc_tickmarks(x, y, 10, &tm); | |
79 | ||
80 | for (i = 0; i < nticks; i++) { | |
81 | printf(" (%s) %g\n", tm[i].string, tm[i].value); | |
82 | } | |
83 | printf("\n\n"); | |
84 | free(tm); | |
85 | } | |
86 | ||
87 | int main(int argc, char *argv[]) | |
88 | { | |
89 | test_range(0.0005, 0.008); | |
90 | test_range(0.5, 0.8); | |
91 | test_range(5.5, 8.8); | |
92 | test_range(50.5, 80.8); | |
93 | test_range(-20, 20.8); | |
94 | test_range(-30, 700.8); | |
95 | } | |
96 | #endif |