7 * adapted from Paul Heckbert's algorithm on p 657-659 of
8 * Andrew S. Glassner's book, "Graphics Gems"
13 #include "tickmarks.h"
15 #define MAX(a, b) (((a) < (b)) ? (b) : (a))
17 static double nicenum(double x, int round)
19 int exp; /* exponent of x */
20 double f; /* fractional part of x */
22 exp = floor(log10(x));
23 f = x / pow(10.0, exp);
26 return 1.0 * pow(10.0, exp);
28 return 2.0 * pow(10.0, exp);
30 return 5.0 * pow(10.0, exp);
31 return 10.0 * pow(10.0, exp);
34 return 1.0 * pow(10.0, exp);
36 return 2.0 * pow(10.0, exp);
38 return 5.0 * pow(10.0, exp);
39 return 10.0 * pow(10.0, exp);
42 static void shorten(struct tickmark *tm, int nticks)
44 int i, l, minshorten, can_shorten_by;
46 char shorten_char = '?';
49 for (i = 0; i < nticks; i++) {
53 if (l > 9 && strcmp(&str[l - 9], "000000000") == 0) {
56 } else if (6 < minshorten && l > 6 &&
57 strcmp(&str[l - 6], "000000") == 0) {
60 } else if (l > 3 && strcmp(&str[l - 3], "000") == 0) {
67 if (can_shorten_by < minshorten)
68 minshorten = can_shorten_by;
74 for (i = 0; i < nticks; i++) {
77 str[l - minshorten] = shorten_char;
78 str[l - minshorten + 1] = '\0';
82 int calc_tickmarks(double min, double max, int nticks, struct tickmark **tm)
86 double d; /* tick mark spacing */
87 double graphmin, graphmax; /* graph range min and max */
91 /* we expect min != max */
92 range = nicenum(max - min, 0);
93 d = nicenum(range / (nticks - 1), 1);
94 graphmin = floor(min / d) * d;
95 graphmax = ceil(max / d) * d;
96 nfrac = MAX(-floor(log10(d)), 0);
97 snprintf(str, sizeof(str)-1, "%%.%df", nfrac);
99 count = ((graphmax + 0.5 * d) - graphmin) / d + 1;
100 *tm = malloc(sizeof(**tm) * count);
103 for (x = graphmin; x < graphmax + 0.5 * d; x += d) {
105 sprintf((*tm)[i].string, str, x);
114 static void test_range(double x, double y)
118 struct tickmark *tm = NULL;
119 printf("Testing range %g - %g\n", x, y);
120 nticks = calc_tickmarks(x, y, 10, &tm);
122 for (i = 0; i < nticks; i++) {
123 printf(" (%s) %g\n", tm[i].string, tm[i].value);
129 int main(int argc, char *argv[])
131 test_range(0.0005, 0.008);
132 test_range(0.5, 0.8);
133 test_range(5.5, 8.8);
134 test_range(50.5, 80.8);
135 test_range(-20, 20.8);
136 test_range(-30, 700.8);