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/*
Fractal cratering
Designed and implemented in November of 1989 by:
John Walker
Autodesk SA
Avenue des Champs-Montants 14b
CH-2074 MARIN
Switzerland
Usenet: kelvin@Autodesk.com
Fax: 038/33 88 15
Voice: 038/33 76 33
The algorithm used to determine crater size is as described on
pages 31 and 32 of:
Peitgen, H.-O., and Saupe, D. eds., The Science Of Fractal
Images, New York: Springer Verlag, 1988.
The mathematical technique used to calculate crater radii that
obey the proper area law distribution from a uniformly distributed
pseudorandom sequence was developed by Rudy Rucker.
Permission to use, copy, modify, and distribute this software and
its documentation for any purpose and without fee is hereby
granted, without any conditions or restrictions. This software is
provided "as is" without express or implied warranty.
PLUGWARE!
If you like this kind of stuff, you may also enjoy "James Gleick's
Chaos--The Software" for MS-DOS, available for $59.95 from your
local software store or directly from Autodesk, Inc., Attn: Science
Series, 2320 Marinship Way, Sausalito, CA 94965, USA. Telephone:
(800) 688-2344 toll-free or, outside the U.S. (415) 332-2344 Ext
4886. Fax: (415) 289-4718. "Chaos--The Software" includes a more
comprehensive fractal forgery generator which creates
three-dimensional landscapes as well as clouds and planets, plus
five more modules which explore other aspects of Chaos. The user
guide of more than 200 pages includes an introduction by James
Gleick and detailed explanations by Rudy Rucker of the mathematics
and algorithms used by each program.
*/
#include <math.h>
#include "pgm.h"
static void gencraters ARGS((void));
static void initseed ARGS((void));
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif
/* Definitions for obtaining random numbers. */
#define Cast(low, high) ((low)+((high)-(low)) * ((random() & 0x7FFF) / arand))
/* Data types */
typedef int Boolean;
#define FALSE 0
#define TRUE 1
#define V (void)
/* Display parameters */
#define SCRX screenxsize /* Screen width */
#define SCRY screenysize /* Screen height */
#define SCRGAMMA 1.0 /* Display gamma */
/* Local variables */
#define ImageGamma 0.5 /* Inherent gamma of mapped image */
static int screenxsize = 256; /* Screen X size */
static int screenysize = 256; /* Screen Y size */
static double dgamma = SCRGAMMA; /* Display gamma */
static double arand = 32767.0; /* Random number parameters */
static long ncraters = 50000L; /* Number of craters to generate */
static double CdepthPower = 1.5; /* Crater depth power factor */
static double DepthBias = 0.707107; /* Depth bias */
/* INITSEED -- Generate initial random seed, if needed. */
static void initseed()
{
int i;
i = time((long *) 0) * 0xF37C;
srandom(i);
for (i = 0; i < 7; i++) {
V random();
}
}
/* GENCRATERS -- Generate cratered terrain. */
static void gencraters()
{
int i, j, x, y;
long l;
unsigned short *aux;
int slopemin = -52, slopemax = 52;
#define RGBQuant 255
unsigned char *slopemap; /* Slope to pixel map */
gray *pixels; /* Pixel vector */
#define Auxadr(x, y) ((unsigned short *) (aux + ((((y)) * SCRX) + (x))))
/* Acquire the elevation array and initialise it to mean
surface elevation. */
aux = (unsigned short *) malloc(SCRX * SCRY * sizeof(short));
if (aux == (unsigned short *) 0) {
pm_error("out of memory allocating elevation array");
}
/* Acquire the elevation buffer and initialise to mean
initial elevation. */
for (i = 0; i < SCRY; i++) {
unsigned short *zax = aux + (((long) SCRX) * i);
for (j = 0; j < SCRX; j++) {
*zax++ = 32767;
}
}
/* Every time we go around this loop we plop another crater
on the surface. */
for (l = 0; l < ncraters; l++) {
double g;
int cx = Cast(0.0, ((double) SCRX - 1)),
cy = Cast(0.0, ((double) SCRY - 1)),
gx, gy, x, y;
unsigned long amptot = 0, axelev;
unsigned int npatch = 0;
/* Phase 1. Compute the mean elevation of the impact
area. We assume the impact area is a
fraction of the total crater size. */
/* Thanks, Rudy, for this equation that maps the uniformly
distributed numbers from Cast into an area-law
distribution as observed on cratered bodies. */
g = sqrt(1 / (M_PI * (1 - Cast(0, 0.9999))));
/* If the crater is tiny, handle it specially. */
if (g < 3) {
/* Set pixel to the average of its Moore neighbourhood. */
for (y = max(0, cy - 1); y <= min(SCRY - 1, cy + 1); y++) {
int sx = max(0, cx - 1);
unsigned short *a = Auxadr(sx, y);
for (x = sx; x <= min(SCRX - 1, cx + 1); x++) {
amptot += *a++;
npatch++;
}
}
axelev = amptot / npatch;
/* Perturb the mean elevation by a small random factor. */
x = (g >= 1) ? ((random() >> 8) & 3) - 1 : 0;
*Auxadr(cx, cy) = axelev + x;
/* Jam repaint sizes to correct patch. */
gx = 1;
gy = 0;
} else {
/* Regular crater. Generate an impact feature of the
correct size and shape. */
/* Determine mean elevation around the impact area. */
gx = max(2, (g / 3));
gy = max(2, g / 3);
for (y = max(0, cy - gy); y <= min(SCRY - 1, cy + gy); y++) {
int sx = max(0, cx - gx);
unsigned short *a = Auxadr(sx, y);
for (x = sx; x <= min(SCRX - 1, cx + gx); x++) {
amptot += *a++;
npatch++;
}
}
axelev = amptot / npatch;
gy = max(2, g);
g = gy;
gx = max(2, g);
for (y = max(0, cy - gy); y <= min(SCRY - 1, cy + gy); y++) {
int sx = max(0, cx - gx);
unsigned short *ax = Auxadr(sx, y);
double dy = (cy - y) / (double) gy,
dysq = dy * dy;
for (x = sx; x <= min(SCRX - 1, cx + gx); x++) {
double dx = ((cx - x) / (double) gx),
cd = (dx * dx) + dysq,
cd2 = cd * 2.25,
tcz = DepthBias - sqrt(fabs(1 - cd2)),
cz = max((cd2 > 1) ? 0.0 : -10, tcz),
roll, iroll;
unsigned short av;
cz *= pow(g, CdepthPower);
if (dy == 0 && dx == 0 && ((int) cz) == 0) {
cz = cz < 0 ? -1 : 1;
}
#define rollmin 0.9
roll = (((1 / (1 - min(rollmin, cd))) /
(1 / (1 - rollmin))) - (1 - rollmin)) / rollmin;
iroll = 1 - roll;
av = (axelev + cz) * iroll + (*ax + cz) * roll;
av = max(1000, min(64000, av));
*ax++ = av;
}
}
}
if ((l % 5000) == 4999) {
pm_message( "%ld craters generated of %ld (%ld%% done)",
l + 1, ncraters, ((l + 1) * 100) / ncraters);
}
}
i = max((slopemax - slopemin) + 1, 1);
slopemap = (unsigned char *) malloc(i * sizeof(unsigned char));
if (slopemap == (unsigned char *) 0) {
pm_error("out of memory allocating slope map");
}
for (i = slopemin; i <= slopemax; i++) {
/* Confused? OK, we're using the left-to-right slope to
calculate a shade based on the sine of the angle with
respect to the vertical (light incident from the left).
Then, with one exponentiation, we account for both the
inherent gamma of the image (ad-hoc), and the
user-specified display gamma, using the identity:
(x^y)^z = (x^(y*z)) */
slopemap[i - slopemin] = i > 0 ?
(128 + 127.0 *
pow(sin((M_PI / 2) * i / slopemax),
dgamma * ImageGamma)) :
(128 - 127.0 *
pow(sin((M_PI / 2) * i / slopemin),
dgamma * ImageGamma));
}
/* Generate the screen image. */
pgm_writepgminit(stdout, SCRX, SCRY, RGBQuant, FALSE);
pixels = pgm_allocrow(SCRX);
for (y = 0; y < SCRY; y++) {
unsigned short *ax = Auxadr(0, y);
gray *pix = pixels;
for (x = 0; x < SCRX - 1; x++) {
int j = ax[1] - ax[0];
j = min(max(slopemin, j), slopemax);
*pix++ = slopemap[j - slopemin];
ax++;
}
pgm_writepgmrow(stdout, pixels, SCRX, RGBQuant, FALSE);
}
pm_close(stdout);
pgm_freerow(pixels);
#undef Auxadr
#undef Scradr
free((char *) slopemap);
free((char *) aux);
}
/* MAIN -- Main program. */
int main(argc, argv)
int argc;
char *argv[];
{
int i;
Boolean gammaspec = FALSE, numspec = FALSE,
widspec = FALSE, hgtspec = FALSE;
char *usage = "[-number <n>] [-width|-xsize <w>]\n\
[-height|-ysize <h>] [-gamma <f>]";
DepthBias = sqrt(0.5); /* Get exact value for depth bias */
pgm_init(&argc, argv);
i = 1;
while ((i < argc) && (argv[i][0] == '-') && (argv[i][1] != '\0')) {
if (pm_keymatch(argv[i], "-gamma", 2)) {
if (gammaspec) {
pm_error("already specified gamma correction");
}
i++;
if ((i == argc) || (sscanf(argv[i], "%lf", &dgamma) != 1))
pm_usage(usage);
if (dgamma <= 0.0) {
pm_error("gamma correction must be greater than 0");
}
gammaspec = TRUE;
} else if (pm_keymatch(argv[i], "-number", 2)) {
if (numspec) {
pm_error("already specified number of craters");
}
i++;
if ((i == argc) || (sscanf(argv[i], "%ld", &ncraters) != 1))
pm_usage(usage);
if (ncraters <= 0) {
pm_error("number of craters must be greater than 0!");
}
numspec = TRUE;
} else if (pm_keymatch(argv[i], "-xsize", 2) ||
pm_keymatch(argv[i], "-width", 2)) {
if (widspec) {
pm_error("already specified a width/xsize");
}
i++;
if ((i == argc) || (sscanf(argv[i], "%d", &screenxsize) != 1))
pm_usage(usage);
if (screenxsize <= 0) {
pm_error("screen width must be greater than 0");
}
widspec = TRUE;
} else if (pm_keymatch(argv[i], "-ysize", 2) ||
pm_keymatch(argv[i], "-height", 2)) {
if (hgtspec) {
pm_error("already specified a height/ysize");
}
i++;
if ((i == argc) || (sscanf(argv[i], "%d", &screenysize) != 1))
pm_usage(usage);
if (screenxsize <= 0) {
pm_error("screen height must be greater than 0");
}
hgtspec = TRUE;
} else {
pm_usage(usage);
}
i++;
}
initseed();
gencraters();
exit(0);
}
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