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>
1 file changed
