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

[Bill Spitzak]

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> wrote:

> On Tue, Dec 22, 2015 at 9:01 PM, Bill Spitzak <spitzak at gmail.com> wrote:
> >
> >
> > On Tue, Dec 22, 2015 at 4:38 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>
> >> >
> >> > 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
> >> > http://lists.freedesktop.org/mailman/listinfo/pixman
> >
> >
>
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