cairo-util.c

/*
 * Copyright © 2008 Kristian Høgsberg
 *
 * 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 <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <math.h>
#include <cairo.h>
#include "cairo-util.h"

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

void
blur_surface(cairo_surface_t *surface, int margin)
{
	int32_t width, height, stride, x, y, z, w;
	uint8_t *src, *dst;
	uint32_t *s, *d, a, p;
	int i, j, k, size, half;
	uint8_t kernel[35];
	double f;

	size = ARRAY_LENGTH(kernel);
	width = cairo_image_surface_get_width(surface);
	height = cairo_image_surface_get_height(surface);
	stride = cairo_image_surface_get_stride(surface);
	src = cairo_image_surface_get_data(surface);

	dst = malloc(height * stride);

	half = size / 2;
	a = 0;
	for (i = 0; i < size; i++) {
		f = (i - half);
		kernel[i] = exp(- f * f / 30.0) * 80;
		a += kernel[i];
	}

	for (i = 0; i < height; i++) {
		s = (uint32_t *) (src + i * stride);
		d = (uint32_t *) (dst + i * stride);
		for (j = 0; j < width; j++) {
			if (margin < j && j < width - margin) {
				d[j] = s[j];
				continue;
			}

			x = 0;
			y = 0;
			z = 0;
			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) * kernel[k];
				y += ((p >> 16) & 0xff) * kernel[k];
				z += ((p >> 8) & 0xff) * kernel[k];
				w += (p & 0xff) * kernel[k];
			}
			d[j] = (x / a << 24) | (y / a << 16) | (z / a << 8) | w / a;
		}
	}

	for (i = 0; i < height; i++) {
		s = (uint32_t *) (dst + i * stride);
		d = (uint32_t *) (src + i * stride);
		for (j = 0; j < width; j++) {
			if (margin <= i && i < height - margin) {
				d[j] = s[j];
				continue;
			}

			x = 0;
			y = 0;
			z = 0;
			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) * stride);
				p = s[j];

				x += (p >> 24) * kernel[k];
				y += ((p >> 16) & 0xff) * kernel[k];
				z += ((p >> 8) & 0xff) * kernel[k];
				w += (p & 0xff) * kernel[k];
			}
			d[j] = (x / a << 24) | (y / a << 16) | (z / a << 8) | w / a;
		}
	}

	free(dst);
}