/*
 * Copyright © 2008 Kristian Høgsberg
 * Copyright © 2009 Chris Wilson
 *
 * Permission to use, copy, modify, distribute, and sell this software and its
 * documentation for any purpose is hereby granted without fee, provided that
 * the above copyright notice appear in all copies and that both that copyright
 * notice and this permission notice appear in supporting documentation, and
 * that the name of the copyright holders not be used in advertising or
 * publicity pertaining to distribution of the software without specific,
 * written prior permission.  The copyright holders make no representations
 * about the suitability of this software for any purpose.  It is provided "as
 * is" without express or implied warranty.
 *
 * THE COPYRIGHT HOLDERS DISCLAIM ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
 * EVENT SHALL THE COPYRIGHT HOLDERS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE,
 * DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
 * TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
 * OF THIS SOFTWARE.
 */

#include <math.h>
#include <stdint.h>

#define ARRAY_LENGTH(a) (sizeof (a) / sizeof (a)[0])

/* Performs a simple 2D Gaussian blur of radius @radius on surface @surface. */
void
blur_image_surface (cairo_surface_t *surface, int radius)
{
    int x, y, z, w;
    uint8_t *src, *dst;
    uint32_t *s, *d, p;
    int i, j, k;
    uint8_t kernel[17];
    const int size = ARRAY_LENGTH (kernel);
    const int half = size / 2;

    if (cairo_surface_status (surface))
    return;

    int width = cairo_image_surface_get_width (surface);
    const int height = cairo_image_surface_get_height (surface);

    switch (cairo_image_surface_get_format (surface)) {
      case CAIRO_FORMAT_A1:
      default:
        /* Don't even think about it! */
        return;
      case CAIRO_FORMAT_A8:
        /* Handle a8 surfaces by effectively unrolling the loops by a
         * factor of 4 - this is safe since we know that stride has to be a
         * multiple of uint32_t. */
        width /= 4;
        break;
      case CAIRO_FORMAT_RGB24:
      case CAIRO_FORMAT_ARGB32:
        break;
    }

    cairo_surface_t *tmp = cairo_image_surface_create (CAIRO_FORMAT_ARGB32, width, height);
    if (cairo_surface_status (tmp))
    return;

    src = cairo_image_surface_get_data (surface);
    const int src_stride = cairo_image_surface_get_stride (surface);

    dst = cairo_image_surface_get_data (tmp);
    const int dst_stride = cairo_image_surface_get_stride (tmp);

    uint32_t a = 0;
    for (i = 0; i < size; i++) {
      const double f = i - half;
      a += kernel[i] = exp (- f * f / 30.0) * 80;
    }

    /* Horizontally blur from surface -> tmp */
    for (i = 0; i < height; i++) {
      s = (uint32_t *) (src + i * src_stride);
      d = (uint32_t *) (dst + i * dst_stride);
      for (j = 0; j < width; j++) {

        x = y = z = w = 0;
        for (k = 0; k < size; k++) {
          if (j - half + k < 0 || j - half + k >= width)
            continue;
          p = s[j - half + k];
          x += ((p >> 24) & 0xff) * kernel[k];
          y += ((p >> 16) & 0xff) * kernel[k];
          z += ((p >>  8) & 0xff) * kernel[k];
          w += ((p >>  0) & 0xff) * kernel[k];
        }
        d[j] = (x / a << 24) | (y / a << 16) | (z / a << 8) | w / a;
      }
    }

    /* Then vertically blur from tmp -> surface */
    for (i = 0; i < height; i++) {
      s = (uint32_t *) (dst + i * dst_stride);
      d = (uint32_t *) (src + i * src_stride);
      for (j = 0; j < width; j++) {

        x = y = z = w = 0;
        for (k = 0; k < size; k++) {
          if (i - half + k < 0 || i - half + k >= height)
            continue;
          s = (uint32_t *) (dst + (i - half + k) * dst_stride);
          p = s[j];
          x += ((p >> 24) & 0xff) * kernel[k];
          y += ((p >> 16) & 0xff) * kernel[k];
          z += ((p >>  8) & 0xff) * kernel[k];
          w += ((p >>  0) & 0xff) * kernel[k];
        }
        d[j] = (x / a << 24) | (y / a << 16) | (z / a << 8) | w / a;
      }
    }
    cairo_surface_destroy (tmp);
    cairo_surface_mark_dirty (surface);
}
