| 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 |