/*
 *  libpipi       Proper image processing implementation library
 *  Copyright (c) 2004-2008 Sam Hocevar <sam@zoy.org>
 *                All Rights Reserved
 *
 *  $Id$
 *
 *  This library is free software. It comes without any warranty, to
 *  the extent permitted by applicable law. You can redistribute it
 *  and/or modify it under the terms of the Do What The Fuck You Want
 *  To Public License, Version 2, as published by Sam Hocevar. See
 *  http://sam.zoy.org/wtfpl/COPYING for more details.
 */

/*
 * blur.c: blur functions
 */

#include "config.h"
#include "common.h"

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

#include "pipi.h"
#include "pipi_internals.h"

pipi_image_t *pipi_gaussian_blur(pipi_image_t const *src, float radius)
{
    pipi_image_t *dst;
    double *kernel;
    double K, L, t = 0.;
    int x, y, i, j, w, h, kr, kw;

    w = src->width;
    h = src->height;

    kr = (int)(3. * radius + 0.99999);
    kw = 2 * kr + 1;
    K = 1. / (2. * M_PI * radius * radius);
    L = -1. / (2. * radius * radius);

    kernel = malloc(kw * kw * sizeof(double));
    for(j = -kr; j <= kr; j++)
        for(i = -kr; i <= kr; i++)
            t += kernel[(j + kr) * kw + (i + kr)]
                     = exp(L * (i * i + j * j)) * K;

    for(j = -kr; j <= kr; j++)
        for(i = -kr; i <= kr; i++)
            kernel[(j + kr) * kw + (i + kr)] /= t;

    dst = pipi_new(w, h);

    for(y = 0; y < h; y++)
    {
        for(x = 0; x < w; x++)
        {
            double R = 0., G = 0., B = 0.;

            for(j = -kr; j <= kr; j++)
                for(i = -kr; i <= kr; i++)
                {
                    double r, g, b, f = kernel[(j + kr) * kw + (i + kr)];

                    pipi_getpixel(src, x + i, y + j, &r, &g, &b);
                    R += f * r;
                    G += f * g;
                    B += f * b;
                }

            pipi_setpixel(dst, x, y, R, G, B);
        }
    }

    return dst;
}