[Pixman] [PATCH 11/15] pixman-filter: made IMPULSE.IMPULSE not produce a zero-wide filter

[Oded Gabbay]

On Tue, Dec 22, 2015 at 9:15 PM, Bill Spitzak <spitzak at gmail.com> wrote:
>
>
> On Tue, Dec 22, 2015 at 4:21 AM, Oded Gabbay <oded.gabbay at gmail.com> wrote:
>>
>> On Sat, Dec 12, 2015 at 8:06 PM,  <spitzak at gmail.com> wrote:
>> > From: Bill Spitzak <spitzak at gmail.com>
>> >
>> > With the other patch to put error on the center pixel, this produces
>> > the same result as BOX.IMPULSE filter.
>> > ---
>> >  pixman/pixman-filter.c | 2 ++
>> >  1 file changed, 2 insertions(+)
>> >
>> > diff --git a/pixman/pixman-filter.c b/pixman/pixman-filter.c
>> > index 00126cd..64981cd 100644
>> > --- a/pixman/pixman-filter.c
>> > +++ b/pixman/pixman-filter.c
>> > @@ -327,7 +327,9 @@ pixman_filter_create_separable_convolution (int
>> > *n_values,
>> >      subsample_y = (1 << subsample_bits_y);
>> >
>> >      width = filter_width (reconstruct_x, sample_x, sx);
>> > +    if (width < 1) width = 1;
>>
>> Please put the assignment in a new line
>
>
> Okay I will get these.
>>
>>
>> >      height = filter_width (reconstruct_y, sample_y, sy);
>> > +    if (height < 1) height = 1;
>>
>> Same comment
>>
>> >
>> >      *n_values = 4 + width * subsample_x + height * subsample_y;
>> >
>> > --
>> > 1.9.1
>> >
>> > _______________________________________________
>> > Pixman mailing list
>> > Pixman at lists.freedesktop.org
>> > http://lists.freedesktop.org/mailman/listinfo/pixman
>>
>> I have the same request as with the other patch (center pixel). I can
>> see the visual difference - the picture in scale demo doesn't
>> disappear when reconstruct & sample are IMPLUSE - but I would like
>> some additional explanation to better understand.
>>
>> In which cases width/height are smaller than 1 ? How does that happen
>> ? How this patch solves it ?
>
>
> The impulse filters have a width of zero (if you could actually plot them
> they are an infinitely thin and infinitely tall line with an area of 1.0).
> Once convolved with any other filter you will get a filter of width 1, with
> a value equal to the other filter at the center of the impulse filter. The
> convolving code detects the impulse filters and calculates this directly (it
> is possible the impulse filter calculating function, which returns 1.0, is
> not necessary as it is never called?).
>
> The proper result of impulse+impulse is 1.0 when the subsample is in the
> pixel center and 0.0 otherwise. But I don't think the result is useful (it
> means there are dots where the pixel centers line up). Also it would require
> the code to handle un-normalized filters which would complicate it a good
> deal. So I just made it produce the same as BOX.IMPULSE (ie nearest pixel).
>
OK, so assuming you fix the above and put this into the commit msg
than this patch is:

Acked-by: Oded Gabbay <oded.gabbay at gmail.com>

>>
>>
>>        Oded
>
>