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pixman-filter: Speed up BOX/BOX filter

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The convolution of two BOX filters is simply the length of the
interval where both are non-zero, so we can simply return width from
the integral() function because the integration region has already
been restricted to be such that both functions are non-zero on it.

This is both faster and more accurate than doing numerical integration.

This patch is based on one by Bill Spitzak

    https://lists.freedesktop.org/archives/pixman/2016-March/004446.html

with these changes:

- Rebased to not assume any changes in the arguments to integral().

- Dropped the multiplication by scale

- Added more details in the commit message.

Signed-off-by: Søren Sandmann <soren.sandmann@gmail.com>
Reviewed-by: Bill Spitzak <spitzak@gmail.com>
This commit is contained in:
Søren Sandmann Pedersen
2016-08-30 22:03:12 -07:00
parent 8855b3a2a2
commit 3b46fce6fe
1 changed files with 5 additions and 1 deletions
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6
pixman/pixman-filter.c
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@@ -160,11 +160,15 @@ integral (pixman_kernel_t kernel1, double x1,
pixman_kernel_t kernel2, double scale, double x2,
double width)
{
if (kernel1 == PIXMAN_KERNEL_BOX && kernel2 == PIXMAN_KERNEL_BOX)
{
return width;
}
/* The LINEAR filter is not differentiable at 0, so if the
* integration interval crosses zero, break it into two
* separate integrals.
*/
if (kernel1 == PIXMAN_KERNEL_LINEAR && x1 < 0 && x1 + width > 0)
else if (kernel1 == PIXMAN_KERNEL_LINEAR && x1 < 0 && x1 + width > 0)
{
return
integral (kernel1, x1, kernel2, scale, x2, - x1) +