pixman-filter: Speed up BOX/BOX filter
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>
diff --git a/pixman/pixman-filter.c b/pixman/pixman-filter.c
index 878cf9d..11e7d0e 100644
--- a/pixman/pixman-filter.c
+++ b/pixman/pixman-filter.c
@@ -160,11 +160,15 @@
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) +
