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/*
* $Id: synth.c 23460 2021-04-11 17:02:45Z yeti-dn $
* Copyright (C) 2021 David Necas (Yeti).
* E-mail: yeti@gwyddion.net.
*
* This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public
* License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any
* later version.
*
* This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
* warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
* details.
*
* You should have received a copy of the GNU General Public License along with this program; if not, write to the
* Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
#include "config.h"
#include <stdlib.h>
#include <libgwyddion/gwymacros.h>
#include <libprocess/datafield.h>
#include <libprocess/filters.h>
#include <libprocess/synth.h>
#include "libgwyddion/gwyomp.h"
/* Iterating through square in a spiral fashion from the origin to preserve the centre conrer if it's randomly
* generated. Field @k holds the current index in the two-dimensional array. */
typedef struct {
gint n;
gint i, j, k;
gint istep, jstep;
gint s, segmentend, ntotalstep;
} GrowingIter;
static inline void
growing_iter_init(GrowingIter *giter, guint n)
{
giter->n = n;
giter->j = giter->i = 0;
giter->istep = 0;
giter->jstep = -1;
giter->ntotalstep = n*n;
giter->segmentend = MIN(1, n*n);
giter->s = 0;
giter->k = (n/2 - giter->i)*n + (giter->j + n/2);
}
static inline gboolean
growing_iter_next(GrowingIter *giter)
{
giter->i += giter->istep;
giter->j += giter->jstep;
giter->k = (giter->n/2 - giter->i)*giter->n + (giter->j + giter->n/2);
giter->s++;
if (giter->s == giter->segmentend) {
if (giter->s == giter->ntotalstep)
return FALSE;
if (giter->i == giter->j + 1) {
giter->istep = 1;
giter->jstep = 0;
giter->segmentend = 1 - 2*giter->i;
}
else if (giter->i == giter->j) {
giter->istep = -1;
giter->jstep = 0;
giter->segmentend = 2*giter->i;
}
else if (giter->j > 0) {
giter->istep = 0;
giter->jstep = -1;
giter->segmentend = 2*giter->j + 1;
}
else {
giter->istep = 0;
giter->jstep = 1;
giter->segmentend = 2*giter->i;
}
giter->segmentend += giter->s;
giter->segmentend = MIN(giter->segmentend, giter->ntotalstep);
}
return TRUE;
}
/* Fill a data field with uncorrelated random numbers in a growing fashion to
* preserve the character of the noise even if the dimensions change */
static void
fill_displacement_map(GwyDataField *dfield, gdouble q, GRand *rng)
{
GrowingIter giter;
guint xres, yres;
gdouble *data;
xres = dfield->xres;
yres = dfield->yres;
data = dfield->data;
g_return_if_fail(xres == yres);
growing_iter_init(&giter, xres);
do {
data[giter.k] = q*(g_rand_double(rng) - 0.5);
} while (growing_iter_next(&giter));
}
/**
* gwy_data_field_synth_gaussian_displacement:
* @data_field: A data field.
* @sigma: Amplitude of displacement (in units of 1, usually meaning pixels).
* @tau: Lateral scale of displacement variation (in pixels).
* @rng: Random number generator.
*
* Fills a data field with correlated Gaussian noise, suitable as displacement field.
*
* The number of calls to @rng is unspecified; it will not be left in any defined state. However, the noise is filled
* from the data field centre. Meaning that changing @tau will zoom in or out the Gaussian noise, preserving the
* centr (whereas changing @sigma simply changes the amplitude).
*
* Since: 2.59
**/
void
gwy_data_field_synth_gaussian_displacement(GwyDataField *data_field,
gdouble sigma, gdouble tau,
GRand *rng)
{
GwyDataField *grid;
guint gn, n, xres, yres;
gdouble q, r;
g_return_if_fail(GWY_IS_DATA_FIELD(data_field));
g_return_if_fail(rng);
xres = data_field->xres;
yres = data_field->yres;
n = MAX(xres, yres);
q = 2.0*sigma*tau;
if (!q) {
gwy_data_field_clear(data_field);
return;
}
if (tau <= 1.0) {
if (xres == yres) {
fill_displacement_map(data_field, q, rng);
gwy_data_field_filter_gaussian(data_field, tau);
return;
}
grid = gwy_data_field_new(n, n, 1.0, 1.0, FALSE);
fill_displacement_map(grid, q, rng);
gwy_data_field_filter_gaussian(grid, tau);
gwy_data_field_area_copy(grid, data_field, (n - xres)/2, (n - yres)/2, xres, yres, 0, 0);
g_object_unref(grid);
return;
}
gn = GWY_ROUND(1.0/tau*n);
gn = MAX(gn, 2);
r = (gdouble)gn/n;
grid = gwy_data_field_new(gn, gn, 1.0, 1.0, FALSE);
fill_displacement_map(grid, q*r, rng);
gwy_data_field_filter_gaussian(grid, r*tau);
gwy_data_field_resample(grid, n, n, GWY_INTERPOLATION_KEY);
gwy_data_field_area_copy(grid, data_field, (n - xres)/2, (n - yres)/2, xres, yres, 0, 0);
g_object_unref(grid);
}
/************************** Documentation ****************************/
/**
* SECTION:synth
* @title: synth
* @short_description: Synthetic data generation
**/
/* vim: set cin columns=120 tw=118 et ts=4 sw=4 cino=>1s,e0,n0,f0,{0,}0,^0,\:1s,=0,g1s,h0,t0,+1s,c3,(0,u0 : */
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