/* creates an butterworth filter.
 *
 * 02/01/14
 * 	- from butterworth.c
 */

/*

	This file is part of VIPS.

	VIPS is free software; you can redistribute it and/or modify
	it under the terms of the GNU Lesser 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 Lesser General Public License for more details.

	You should have received a copy of the GNU Lesser 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

 */

/*

	These files are distributed with VIPS - http://www.vips.ecs.soton.ac.uk

 */

/*
#define VIPS_DEBUG
 */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif /*HAVE_CONFIG_H*/
#include <glib/gi18n-lib.h>

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>

#include <vips/vips.h>

#include "pcreate.h"
#include "point.h"
#include "pmask.h"

G_DEFINE_TYPE(VipsMaskButterworth, vips_mask_butterworth,
	VIPS_TYPE_MASK);

static double
vips_mask_butterworth_point(VipsMask *mask, double dx, double dy)
{
	VipsMaskButterworth *butterworth = (VipsMaskButterworth *) mask;
	double order = butterworth->order;
	double fc = butterworth->frequency_cutoff;
	double ac = butterworth->amplitude_cutoff;

	double cnst = (1.0 / ac) - 1.0;
	double fc2 = fc * fc;
	double d = dx * dx + dy * dy;

	if (d == 0)
		return 0;
	else
		return 1.0 / (1.0 + cnst * pow(fc2 / d, order));
}

static void
vips_mask_butterworth_class_init(VipsMaskButterworthClass *class)
{
	GObjectClass *gobject_class = G_OBJECT_CLASS(class);
	VipsObjectClass *vobject_class = VIPS_OBJECT_CLASS(class);
	VipsMaskClass *mask_class = VIPS_MASK_CLASS(class);

	gobject_class->set_property = vips_object_set_property;
	gobject_class->get_property = vips_object_get_property;

	vobject_class->nickname = "mask_butterworth";
	vobject_class->description = _("make a butterworth filter");

	mask_class->point = vips_mask_butterworth_point;

	VIPS_ARG_DOUBLE(class, "order", 6,
		_("Order"),
		_("Filter order"),
		VIPS_ARGUMENT_REQUIRED_INPUT,
		G_STRUCT_OFFSET(VipsMaskButterworth, order),
		1.0, 1000000.0, 1.0);

	VIPS_ARG_DOUBLE(class, "frequency_cutoff", 7,
		_("Frequency cutoff"),
		_("Frequency cutoff"),
		VIPS_ARGUMENT_REQUIRED_INPUT,
		G_STRUCT_OFFSET(VipsMaskButterworth, frequency_cutoff),
		0.0, 1000000.0, 0.5);

	VIPS_ARG_DOUBLE(class, "amplitude_cutoff", 8,
		_("Amplitude cutoff"),
		_("Amplitude cutoff"),
		VIPS_ARGUMENT_REQUIRED_INPUT,
		G_STRUCT_OFFSET(VipsMaskButterworth, amplitude_cutoff),
		0.0, 1.0, 0.5);
}

static void
vips_mask_butterworth_init(VipsMaskButterworth *butterworth)
{
	butterworth->order = 1.0;
	butterworth->frequency_cutoff = 0.5;
	butterworth->amplitude_cutoff = 0.5;
}

/**
 * vips_mask_butterworth:
 * @out: (out): output image
 * @width: image size
 * @height: image size
 * @order: filter order
 * @frequency_cutoff: frequency threshold
 * @amplitude_cutoff: amplitude threshold
 * @...: %NULL-terminated list of optional named arguments
 *
 * Optional arguments:
 *
 * * @nodc: don't set the DC pixel
 * * @reject: invert the filter sense
 * * @optical: coordinates in optical space
 * * @uchar: output a uchar image
 *
 * Make an butterworth high- or low-pass filter, that is, one with a variable,
 * smooth transition
 * positioned at @frequency_cutoff, where @frequency_cutoff is in
 * range 0 - 1. The shape of the curve is controlled by
 * @order --- higher values give a sharper transition. See Gonzalez and Wintz,
 * Digital Image Processing, 1987.
 *
 * See also: vips_mask_ideal().
 *
 * Returns: 0 on success, -1 on error
 */
int
vips_mask_butterworth(VipsImage **out, int width, int height,
	double order, double frequency_cutoff, double amplitude_cutoff, ...)
{
	va_list ap;
	int result;

	va_start(ap, amplitude_cutoff);
	result = vips_call_split("mask_butterworth", ap,
		out, width, height,
		order, frequency_cutoff, amplitude_cutoff);
	va_end(ap);

	return result;
}
