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cairoblur: Fix the blur again once more

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The differences between the mutter and GTK+ code are subtle, but it
turns out that _gtk_cairo_blur_compute_pixels actually returns the
shadow *spread*. Since we use a triple box blur, the constant was
multiplied by 1.5 to approximate three chained box blurs. Split this
out and use the correct value for the lobe width.
This commit is contained in:
Jasper St. Pierre 2014-10-27 10:18:37 -07:00
parent ac9ac55555
commit 5f40f58c36
1 changed files with 20 additions and 5 deletions
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25
gtk/gtkcairoblur.c
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@ -140,6 +140,23 @@ flip_buffer (guchar *dst_buffer,
#undef BLOCK_SIZE
}
/*
* Gets the size for a single box blur.
*
* Much of this, the 3 * sqrt(2 * pi) / 4, is the known value for
* approximating a Gaussian using box blurs. This yields quite a good
* approximation for a Gaussian. For more details, see:
* http://www.w3.org/TR/SVG11/filters.html#feGaussianBlurElement
* https://bugzilla.mozilla.org/show_bug.cgi?id=590039#c19
*/
#define GAUSSIAN_SCALE_FACTOR ((3.0 * sqrt(2 * G_PI) / 4))
static int
get_box_filter_size (double radius)
{
return GAUSSIAN_SCALE_FACTOR * radius;
}
static void
_boxblur (guchar *buffer,
int width,
@ -147,7 +164,7 @@ _boxblur (guchar *buffer,
int radius)
{
guchar *flipped_buffer;
int d = _gtk_cairo_blur_compute_pixels (radius);
int d = get_box_filter_size (radius);
flipped_buffer = g_malloc (width * height);
@ -210,7 +227,7 @@ _gtk_cairo_blur_surface (cairo_surface_t* surface,
*
* This is just the number of pixels added by the blur radius, shadow
* offset and spread are not included.
*
*
* Much of this, the 3 * sqrt(2 * pi) / 4, is the known value for
* approximating a Gaussian using box blurs. This yields quite a good
* approximation for a Gaussian. Then we multiply this by 1.5 since our
@ -219,10 +236,8 @@ _gtk_cairo_blur_surface (cairo_surface_t* surface,
* http://www.w3.org/TR/SVG11/filters.html#feGaussianBlurElement
* https://bugzilla.mozilla.org/show_bug.cgi?id=590039#c19
*/
#define GAUSSIAN_SCALE_FACTOR ((3.0 * sqrt(2 * G_PI) / 4) * 1.5)
int
_gtk_cairo_blur_compute_pixels (double radius)
{
return floor (radius * GAUSSIAN_SCALE_FACTOR + 0.5);
return floor (radius * GAUSSIAN_SCALE_FACTOR * 1.5 + 0.5);
}