[Pixman] [PATCH v14 10/22] pixman-filter: Correct integration with impulse filters

Bill Spitzak spitzak at gmail.com
Mon Mar 21 16:29:51 UTC 2016

On Sun, Mar 20, 2016 at 11:36 PM, Søren Sandmann <soren.sandmann at gmail.com>

> On Sun, Mar 6, 2016 at 8:06 PM, <spitzak at gmail.com> wrote:
>> From: Bill Spitzak <spitzak at gmail.com>
>> The IMPULSE special-cases did not sample the center of the of the region.
>> This
>> caused it to sample the filters outside their range, and produce
>> assymetric
>> filters and other errors. Fixing this required changing the arguments to
>> integral() so the correct point could be determined.
> I don't understand what is wrong and why this patch fixes it. Which region
> precisely did not have its center sampled? When IMPULSE filters are
> involved the width of the integral is 0 so there isn't really any "region"
> to sample.
> Can you give a concrete example where the previous code produced
> asymmetric filters? Also, what "other errors" was produced? I think these
> examples should be added to the commit log.

It sampled the *other* filter (the one that is not impulse) at the left
edge of the region being passed, rather than at the location of the center
of the impulse filter. This was detected by putting asserts in the filter
functions to see if they were being called outside their width.

> Søren
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