[Pixman] [PATCH 13/15] pixman-filter: refactor cubic polynominal and don't range check

[Bill Spitzak]

Indeed, further tests reveal there was a bug if one of the filters is 
IMPULSE. It was not sampling at the center of the filter, but instead 
offset by the width. I have a patch to fix this that will be in the next 
set.

On 12/26/2015 08:05 PM, Bill Spitzak wrote:
> Sounds like I better look at this more carefully, it is quite possible
> it is producing bad filters but with small enough error that the images
> look OK.
>
> On Dec 23, 2015 5:25 AM, "Oded Gabbay" <oded.gabbay at gmail.com
> <mailto:oded.gabbay at gmail.com>> wrote:
>
>     On Tue, Dec 22, 2015 at 9:01 PM, Bill Spitzak <spitzak at gmail.com
>     <mailto:spitzak at gmail.com>> wrote:
>      >
>      >
>      > On Tue, Dec 22, 2015 at 4:38 AM, Oded Gabbay
>     <oded.gabbay at gmail.com <mailto:oded.gabbay at gmail.com>> wrote:
>      >>
>      >> On Sat, Dec 12, 2015 at 8:06 PM,  <spitzak at gmail.com
>     <mailto:spitzak at gmail.com>> wrote:
>      >> > From: Bill Spitzak <spitzak at gmail.com <mailto:spitzak at gmail.com>>
>      >> >
>      >> > The other filters do not check for x being in range, so there is
>      >> > no reason for cubic to do so.
>      >>
>      >> This argument is a bit problematic.
>      >> We could also argue that this filter was actually implemented
>      >> correctly/more robust and we should add checks for x to the other
>      >> filters.
>      >>
>      >> I fail to see how this saves us much except from removing a
>     condition
>      >> in a very specific path.
>      >>
>      >> Do you argue that ax will never ever be >=2 ?
>      >
>      >
>      > Yes, because if that could happen, then out-of-range x could also
>     be sent to
>      > the other filter functions that are not doing the range check.
>      >
>     I run the scale demo, and added a printf everytime ax is >=2.
>     I got a LOT of prints...
>     So I don't think your argument is correct.
>
>      > Adding range checks to all the other filters (especially the ones
>     that
>      > return constants) would add a bunch of conditions that are never
>     used.
>
>     Maybe, but it might be necessary to produce more accurate results ?
>
>     Oded
>
>
>      >
>      >>
>      >>
>      >>    Oded
>      >>
>      >> > ---
>      >> >  pixman/pixman-filter.c | 16 +++++++---------
>      >> >  1 file changed, 7 insertions(+), 9 deletions(-)
>      >> >
>      >> > diff --git a/pixman/pixman-filter.c b/pixman/pixman-filter.c
>      >> > index 7e10108..bf9dce3 100644
>      >> > --- a/pixman/pixman-filter.c
>      >> > +++ b/pixman/pixman-filter.c
>      >> > @@ -109,18 +109,16 @@ general_cubic (double x, double B, double C)
>      >> >
>      >> >      if (ax < 1)
>      >> >      {
>      >> > -       return ((12 - 9 * B - 6 * C) * ax * ax * ax +
>      >> > -               (-18 + 12 * B + 6 * C) * ax * ax + (6 - 2 *
>     B)) / 6;
>      >> > -    }
>      >> > -    else if (ax >= 1 && ax < 2)
>      >> > -    {
>      >> > -       return ((-B - 6 * C) * ax * ax * ax +
>      >> > -               (6 * B + 30 * C) * ax * ax + (-12 * B - 48 * C) *
>      >> > -               ax + (8 * B + 24 * C)) / 6;
>      >> > +       return (((12 - 9 * B - 6 * C) * ax +
>      >> > +                (-18 + 12 * B + 6 * C)) * ax * ax +
>      >> > +               (6 - 2 * B)) / 6;
>      >> >      }
>      >> >      else
>      >> >      {
>      >> > -       return 0;
>      >> > +       return ((((-B - 6 * C) * ax +
>      >> > +                (6 * B + 30 * C)) * ax +
>      >> > +               (-12 * B - 48 * C)) * ax +
>      >> > +               (8 * B + 24 * C)) / 6;
>      >> >      }
>      >> >  }
>      >> >
>      >> > --
>      >> > 1.9.1
>      >> >
>      >> > _______________________________________________
>      >> > Pixman mailing list
>      >> > Pixman at lists.freedesktop.org <mailto:Pixman at lists.freedesktop.org>
>      >> > http://lists.freedesktop.org/mailman/listinfo/pixman
>      >
>      >
>