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(char *str)
47 if (l > 9 && strcmp(&str[l - 9], "000000000") == 0) {
50 } else if (l > 9 && strcmp(&str[l - 6], "000000") == 0) {
53 } else if (l > 9 && strcmp(&str[l - 3], "000") == 0) {
59 int calc_tickmarks(double min, double max, int nticks, struct tickmark **tm)
63 double d; /* tick mark spacing */
64 double graphmin, graphmax; /* graph range min and max */
68 /* we expect min != max */
69 range = nicenum(max - min, 0);
70 d = nicenum(range / (nticks - 1), 1);
71 graphmin = floor(min / d) * d;
72 graphmax = ceil(max / d) * d;
73 nfrac = MAX(-floor(log10(d)), 0);
74 snprintf(str, sizeof(str)-1, "%%.%df", nfrac);
76 count = ((graphmax + 0.5 * d) - graphmin) / d + 1;
77 *tm = malloc(sizeof(**tm) * count);
80 for (x = graphmin; x < graphmax + 0.5 * d; x += d) {
82 sprintf((*tm)[i].string, str, x);
83 shorten((*tm)[i].string);
91 static void test_range(double x, double y)
95 struct tickmark *tm = NULL;
96 printf("Testing range %g - %g\n", x, y);
97 nticks = calc_tickmarks(x, y, 10, &tm);
99 for (i = 0; i < nticks; i++) {
100 printf(" (%s) %g\n", tm[i].string, tm[i].value);
106 int main(int argc, char *argv[])
108 test_range(0.0005, 0.008);
109 test_range(0.5, 0.8);
110 test_range(5.5, 8.8);
111 test_range(50.5, 80.8);
112 test_range(-20, 20.8);
113 test_range(-30, 700.8);