[Pixman] [PATCH 12/15] pixman-filter: Turn off subsampling when not necessary

[Oded Gabbay]

On Tue, Dec 22, 2015 at 8:59 PM, Bill Spitzak <spitzak at gmail.com> wrote:
>
>
> On Tue, Dec 22, 2015 at 4:44 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>
>> >
>> > If sample is IMPULSE and reconstruct is BOX or IMPULSE the sub-pixel
>> > position of the sample is not relevant, so only one subsample is needed.
>> Why ?
>> I mean why it is not relevant ? and why only one subsample is needed ?
>
>
> Because all the filters for all the subsample positions are the same (a
> single 1).
>
> Actually though, the code is indicating this is happening by returning a
> width of zero. But I think that is not necessary: if the filter width is 1,
> and the filters are normalized so they sum to 1, then all the filters must
> be equal and be a single 1. So I think the filter_width function can return
> 1 and the caller treats all values <= 1 as an indication that subsampling is
> not needed.
hmm, so I guess you will send a modified version of this patch then ?

>
>> Oded
>> > ---
>> >  pixman/pixman-filter.c | 12 +++++++-----
>> >  1 file changed, 7 insertions(+), 5 deletions(-)
>> >
>> > diff --git a/pixman/pixman-filter.c b/pixman/pixman-filter.c
>> > index 64981cd..7e10108 100644
>> > --- a/pixman/pixman-filter.c
>> > +++ b/pixman/pixman-filter.c
>> > @@ -230,6 +230,8 @@ filter_width (pixman_kernel_t reconstruct,
>> >               pixman_kernel_t sample,
>> >               double scale)
>> >  {
>> > +    if (reconstruct == PIXMAN_KERNEL_BOX && sample ==
>> > PIXMAN_KERNEL_IMPULSE)
>> > +       return 0;
>> >      return ceil (scale * filters[sample].width +
>> > filters[reconstruct].width);
>> >  }
>> >
>> > @@ -323,13 +325,13 @@ pixman_filter_create_separable_convolution (int
>> > *n_values,
>> >      int subsample_x, subsample_y;
>> >      int width, height;
>> >
>> > -    subsample_x = (1 << subsample_bits_x);
>> > -    subsample_y = (1 << subsample_bits_y);
>> > -
>> >      width = filter_width (reconstruct_x, sample_x, sx);
>> > -    if (width < 1) width = 1;
>> > +    if (width < 1) { width = 1; subsample_bits_x = 0; }
>> >      height = filter_width (reconstruct_y, sample_y, sy);
>> > -    if (height < 1) height = 1;
>> > +    if (height < 1) { height = 1; subsample_bits_y = 0; }
>> > +
>> > +    subsample_x = (1 << subsample_bits_x);
>> > +    subsample_y = (1 << subsample_bits_y);
>> >
>> >      *n_values = 4 + width * subsample_x + height * subsample_y;
>> >
>> > --
>> > 1.9.1
>> >
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>
>