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

[Oded Gabbay]

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
>> >
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>
>