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Diffstat (limited to 'generator/pamcrater.c')
| -rw-r--r-- | generator/pamcrater.c | 428 |
1 files changed, 428 insertions, 0 deletions
diff --git a/generator/pamcrater.c b/generator/pamcrater.c new file mode 100644 index 00000000..d61ce548 --- /dev/null +++ b/generator/pamcrater.c @@ -0,0 +1,428 @@ +/*============================================================================= + pamcrater +=============================================================================== + Fractal cratering + + This is derived from John Walker's 'pgmcrater' which not only creates + the terrain map as this program does, but then does a relief filter to + convert it to a shaded visual image. + + 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. + + The original program carried this attribution and license: + + 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 + + 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. + +=============================================================================*/ + +/* Modifications by Arjen Bax, 2001-06-21: Remove black vertical line at + right edge. Make craters wrap around the image (enables tiling of image). + */ + +#define _XOPEN_SOURCE /* get M_PI in math.h */ + +#include <assert.h> +#include <math.h> + +#include "pm_c_util.h" +#include "mallocvar.h" +#include "shhopt.h" +#include "nstring.h" +#include "pam.h" + + +struct CmdlineInfo { + /* All the information the user supplied in the command line, + in a form easy for the program to use. + */ + unsigned int number; + unsigned int height; + unsigned int width; + unsigned int randomseedSpec; + unsigned int randomseed; + unsigned int test; + unsigned int radius; +}; + + + +static void +parseCommandLine(int argc, const char ** const argv, + struct CmdlineInfo * const cmdlineP) { +/*---------------------------------------------------------------------------- + Note that the file spec array we return is stored in the storage that + was passed to us as the argv array. +-----------------------------------------------------------------------------*/ + optEntry * option_def; + /* Instructions to OptParseOptions3 on how to parse our options. + */ + optStruct3 opt; + unsigned int option_def_index; + + unsigned int numberSpec, heightSpec, widthSpec, radiusSpec; + + MALLOCARRAY_NOFAIL(option_def, 100); + + option_def_index = 0; /* incremented by OPTENT3 */ + OPTENT3(0, "number", OPT_UINT, &cmdlineP->number, + &numberSpec, 0); + OPTENT3(0, "height", OPT_UINT, &cmdlineP->height, + &heightSpec, 0); + OPTENT3(0, "width", OPT_UINT, &cmdlineP->width, + &widthSpec, 0); + OPTENT3(0, "randomseed", OPT_UINT, &cmdlineP->randomseed, + &cmdlineP->randomseedSpec, 0); + OPTENT3(0, "test", OPT_FLAG, NULL, + &cmdlineP->test, 0); + OPTENT3(0, "radius", OPT_UINT, &cmdlineP->radius, + &radiusSpec, 0); + + opt.opt_table = option_def; + opt.short_allowed = FALSE; /* We have no short (old-fashioned) options */ + opt.allowNegNum = FALSE; /* We may have parms that are negative numbers */ + + pm_optParseOptions3(&argc, (char **)argv, opt, sizeof(opt), 0); + /* Uses and sets argc, argv, and some of *cmdlineP and others. */ + + if (argc-1 > 0) + pm_error("There are no non-option arguments. You specified %u", + argc-1); + + if (!heightSpec) + cmdlineP->height = 256; + + if (cmdlineP->height == 0) + pm_error("-height must be positive"); + + if (!widthSpec) + cmdlineP->width = 256; + + if (cmdlineP->width == 0) + pm_error("-width must be positive"); + + if (cmdlineP->test) { + if (!radiusSpec) + pm_error("With -test, you must specify -radius"); + else { + if(MAX(cmdlineP->height, cmdlineP->width) * 2 < cmdlineP->radius) + pm_error("Radius (%u) too large", cmdlineP->radius); + + if (numberSpec) + pm_error("-number is meaningless with -test"); + + if (cmdlineP->randomseedSpec) + pm_error("-randomseed is meaningless with -test"); + } + } else { + if (radiusSpec) + pm_error("-radius is meaningful only with -test"); + + if (!numberSpec) + cmdlineP->number = 50000; + + if (cmdlineP->number == 0) + pm_error("-number must be positive"); + } + free(option_def); +} + + +/* Definitions for obtaining random numbers. */ + +/* Display parameters */ + +static double const arand = 32767.0; /* Random number parameters */ +static double const CdepthPower = 1.5; /* Crater depth power factor */ +static double const DepthBias2 = 0.5; /* Square of depth bias */ + + + +static double const +cast(double const high) { + + return high * ((rand() & 0x7FFF) / arand); +} + + + +static unsigned int +mod(int const t, + unsigned int const n) { + + /* This is used to transform coordinates beyond bounds into ones + within: craters "wrap around" the edges. This enables tiling + of the image. + + Produces strange effects when crater radius is very large compared + to image size. + */ + + int m; + + m = t % (int)n; + + if (m < 0) + m += n; + + return m; +} + + + +static sample * +terrainModP(struct pam * const pamP, + tuple ** const terrain, + int const x, + int const y) { + + return &terrain[mod(y, pamP->height)][mod(x, pamP->width)][0]; +} + + + + +static sample +terrainMod(struct pam * const pamP, + tuple ** const terrain, + int const x, + int const y) { + + return *terrainModP(pamP, terrain, x, y); +} + + + +static void +smallCrater(struct pam * const pamP, + tuple ** const terrain, + int const cx, + int const cy, + double const g) { +/*---------------------------------------------------------------------------- + Generate a crater with a special method for tiny craters. +-----------------------------------------------------------------------------*/ + int y; + unsigned int amptot; + unsigned int npatch; + + /* Set pixel to the average of its Moore neighborhood. */ + + for (y = cy - 1, amptot = 0, npatch = 0; y <= cy + 1; ++y) { + int x; + for (x = cx - 1; x <= cx + 1; ++x) { + amptot += terrainMod(pamP, terrain, x, y); + ++npatch; + } + } + { + unsigned int const axelev = amptot / npatch; + + /* Perturb the mean elevation by a small random factor. */ + + int const x = g >= 1 ? ((rand() >> 8) & 3) - 1 : 0; + *terrainModP(pamP, terrain, cx, cy) = axelev + x; + } +} + + + +static void +normalCrater(struct pam * const pamP, + tuple ** const terrain, + int const cx, + int const cy, + double const radius) { +/*---------------------------------------------------------------------------- + Generate a regular (not tiny) crater. + + Generate an impact feature of the correct size and shape. +-----------------------------------------------------------------------------*/ + int const impactRadius = (int) MAX(2, (radius / 3)); + int const craterRadius = (int) radius; + double const rollmin = 0.9; + + int y; + unsigned int amptot, axelev; + unsigned int npatch; + + /* Determine mean elevation around the impact area. + We assume the impact area is a fraction of the total crater size. */ + + for (y = cy - impactRadius, amptot = 0, npatch = 0; + y <= cy + impactRadius; + ++y) { + int x; + for (x = cx - impactRadius; x <= cx + impactRadius; ++x) { + amptot += terrainMod(pamP, terrain, x, y); + ++npatch; + } + } + assert(npatch > 0); + axelev = amptot / npatch; + + for (y = cy - craterRadius; y <= cy + craterRadius; ++y) { + int const dysq = (cy - y) * (cy - y); + + int x; + + for (x = cx - craterRadius; x <= cx + craterRadius; ++x) { + int const dxsq = (cx - x) * (cx - x); + double const cd = (dxsq + dysq) / + (double) (craterRadius * craterRadius); + double const cd2 = cd * 2.25; + double const tcz = sqrt(DepthBias2) - sqrt(fabs(1 - cd2)); + double cz; + double roll; + + cz = MAX((cd2 > 1) ? 0.0 : -10, tcz); /* Initial value */ + + cz *= pow(craterRadius, CdepthPower); + if (dysq == 0 && dxsq == 0 && ((int) cz) == 0) { + cz = cz < 0 ? -1 : 1; + } + + roll = (((1 / (1 - MIN(rollmin, cd))) / + (1 / (1 - rollmin))) - (1 - rollmin)) / rollmin; + + { + unsigned int av; + av = (axelev + cz) * (1 - roll) + + (terrainMod(pamP, terrain, x, y) + cz) * roll; + av = MAX(1000, MIN(64000, av)); + + *terrainModP(pamP, terrain, x, y) = av; + } + } + } +} + + + +/* We should also have largeCrater() */ + + + +static void +plopCrater(struct pam * const pamP, + tuple ** const terrain, + int const cx, + int const cy, + double const radius) { + + if (radius < 3) + smallCrater (pamP, terrain, cx, cy, radius); + else + normalCrater(pamP, terrain, cx, cy, radius); +} + + + +static void +genCraters(struct CmdlineInfo const cmdline) { +/*---------------------------------------------------------------------------- + Generate cratered terrain +-----------------------------------------------------------------------------*/ + tuple ** terrain; /* elevation array */ + unsigned int row; + struct pam pam; + + /* Allocate the elevation array and initialize it to mean surface + elevation. + */ + + pam.size = sizeof(pam); + pam.len = PAM_STRUCT_SIZE(tuple_type); + pam.file = stdout; + pam.format = PAM_FORMAT; + pam.height = cmdline.height; + pam.width = cmdline.width; + pam.depth = 1; + pam.maxval = 65535; + pam.bytes_per_sample = 2; + STRSCPY(pam.tuple_type, "elevation"); + + terrain = pnm_allocpamarray(&pam); + + for (row = 0; row < pam.height; ++row) { + unsigned int col; + for (col = 0; col < pam.width; ++col) + terrain[row][col][0] = pam.maxval / 2; + } + + if (cmdline.test) + plopCrater(&pam, terrain, + pam.width/2, pam.height/2, (double) cmdline.radius); + else { + unsigned int const ncraters = cmdline.number; /* num of craters */ + unsigned int l; + + for (l = 0; l < ncraters; ++l) { + int const cx = cast((double) pam.width - 1); + int const cy = cast((double) pam.height - 1); + + /* Thanks, Rudy, for this equation that maps the uniformly + distributed numbers from cast() into an area-law distribution + as observed on cratered bodies. + + Produces values within the interval: + 0.56419 <= radius <= 56.419 + */ + double const radius = sqrt(1 / (M_PI * (1 - cast(0.9999)))); + + plopCrater(&pam, terrain, cx, cy, radius); + + if (((l + 1) % 100000) == 0) + pm_message("%u craters generated of %u (%u%% done)", + l + 1, ncraters, ((l + 1) * 100) / ncraters); + } + } + + pnm_writepam(&pam, terrain); + + pnm_freepamarray(terrain, &pam); + + pm_close(stdout); +} + + + +int +main(int argc, const char ** argv) { + + struct CmdlineInfo cmdline; + + pm_proginit(&argc, argv); + + parseCommandLine(argc, argv, &cmdline); + + srand(cmdline.randomseedSpec ? cmdline.randomseed : pm_randseed()); + + genCraters(cmdline); + + return 0; +} + + + |