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blur.c
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/*
* 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 "blur.h"
/* Performs a simple 2D Gaussian blur of standard devation @sigma surface @surface. */
void
blur_image_surface (cairo_surface_t *surface, int sigma)
{
cairo_surface_t *tmp;
int width, height;
uint32_t *src, *dst;
if (cairo_surface_status (surface))
return;
width = cairo_image_surface_get_width (surface);
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;
}
tmp = cairo_image_surface_create (CAIRO_FORMAT_ARGB32, width, height);
if (cairo_surface_status (tmp))
return;
src = (uint32_t*)cairo_image_surface_get_data (surface);
dst = (uint32_t*)cairo_image_surface_get_data (tmp);
// according to a paper by Peter Kovesi [1], box filter of width w, equals to Gaussian blur of following sigma:
// σ_av = sqrt((w*w-1)/12)
// for our 7x7 filter we have σ_av = 2.0.
// applying the same Gaussian filter n times results in σ_n = sqrt(n*σ_av*σ_av) [2]
// after some trivial math, we arrive at n = ((σ_d)/(σ_av))^2
// since it's a box blur filter, n >= 3
//
// [1]: http://www.peterkovesi.com/papers/FastGaussianSmoothing.pdf
// [2]: https://en.wikipedia.org/wiki/Gaussian_blur#Mathematics
int n = lrintf((sigma*sigma)/(SIGMA_AV*SIGMA_AV));
if (n < 3) n = 3;
for (int i = 0; i < n; i++)
{
// horizontal pass includes image transposition:
// instead of writing pixel src[x] to dst[x],
// we write it to transposed location.
// (to be exact: dst[height * current_column + current_row])
#ifdef __SSE2__
blur_impl_horizontal_pass_sse2(src, dst, width, height);
blur_impl_horizontal_pass_sse2(dst, src, height, width);
#else
blur_impl_horizontal_pass_generic(src, dst, width, height);
blur_impl_horizontal_pass_generic(dst, src, height, width);
#endif
}
cairo_surface_destroy (tmp);
cairo_surface_flush (surface);
cairo_surface_mark_dirty (surface);
}
void blur_impl_horizontal_pass_generic(uint32_t *src, uint32_t *dst, int width, int height) {
uint32_t *o_src = src;
for (int row = 0; row < height; row++) {
for (int column = 0; column < width; column++, src++) {
uint32_t rgbaIn[KERNEL_SIZE + 1];
// handle borders
int leftBorder = column < HALF_KERNEL;
int rightBorder = column > width - HALF_KERNEL;
int i = 0;
if (leftBorder) {
// for kernel size 7x7 and column == 0, we have:
// x x x P0 P1 P2 P3
// first loop mirrors P{0..3} to fill x's,
// second one loads P{0..3}
for (; i < HALF_KERNEL - column; i++)
rgbaIn[i] = *(src + (HALF_KERNEL - i));
for (; i < KERNEL_SIZE; i++)
rgbaIn[i] = *(src - (HALF_KERNEL - i));
} else if (rightBorder) {
for (; i < width - column; i++)
rgbaIn[i] = *(src + i);
for (int k = 0; i < KERNEL_SIZE; i++, k++)
rgbaIn[i] = *(src - k);
} else {
for (; i < KERNEL_SIZE; i++) {
if ((uintptr_t) ((src + 4*i - HALF_KERNEL) + 1)
> (uintptr_t) (o_src + (height * width)))
break;
rgbaIn[i] = *(src + i - HALF_KERNEL);
}
}
uint32_t acc[4] = {0};
for (i = 0; i < KERNEL_SIZE; i++) {
acc[0] += (rgbaIn[i] & 0xFF000000) >> 24;
acc[1] += (rgbaIn[i] & 0x00FF0000) >> 16;
acc[2] += (rgbaIn[i] & 0x0000FF00) >> 8;
acc[3] += (rgbaIn[i] & 0x000000FF) >> 0;
}
for(i = 0; i < 4; i++)
acc[i] *= 1.0/KERNEL_SIZE;
*(dst + height * column + row) = (acc[0] << 24) |
(acc[1] << 16) |
(acc[2] << 8 ) |
(acc[3] << 0);
}
}
}