[cairo] [PATCH pixman 11/13] pixman-filter: Gaussian fixes

Bill Spitzak spitzak at gmail.com
Thu Sep 11 19:12:28 PDT 2014

Simplified the function.

Expanded size slightly (from ~4.25 to 5) to make the cutoff less noticable.
The filter is truncated at a value of .001 instead of .006, this new
value is less than 1/2 of 1/255, rather than greater than it.
---
pixman/pixman-filter.c |    7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/pixman/pixman-filter.c b/pixman/pixman-filter.c
index d763138..dcbed11 100644
--- a/pixman/pixman-filter.c
+++ b/pixman/pixman-filter.c
@@ -63,10 +63,7 @@ linear_kernel (double x)
static double
gaussian_kernel (double x)
{
-#define SQRT2 (1.4142135623730950488016887242096980785696718753769480)
-#define SIGMA (SQRT2 / 2.0)
-
-    return exp (- x * x / (2 * SIGMA * SIGMA)) / (SIGMA * sqrt (2.0 * M_PI));
+    return exp (- x * x) / sqrt (M_PI);
}

static double
@@ -141,7 +138,7 @@ static const filter_info_t filters[] =
{ PIXMAN_KERNEL_BOX,	        box_kernel,       1.0 },
{ PIXMAN_KERNEL_LINEAR,	        linear_kernel,    2.0 },
{ PIXMAN_KERNEL_CUBIC,		cubic_kernel,     4.0 },
-    { PIXMAN_KERNEL_GAUSSIAN,	        gaussian_kernel,  6 * SIGMA },
+    { PIXMAN_KERNEL_GAUSSIAN,	        gaussian_kernel,  5.0 },
{ PIXMAN_KERNEL_LANCZOS2,	        lanczos2_kernel,  4.0 },
{ PIXMAN_KERNEL_LANCZOS3,	        lanczos3_kernel,  6.0 },
{ PIXMAN_KERNEL_LANCZOS3_STRETCHED, nice_kernel,      8.0 },
--
1.7.9.5