[Pixman] [PATCH 10/15] pixman-filter: don't range-check impulse filter

[Oded Gabbay]

On Tue, Dec 22, 2015 at 9:25 PM, Bill Spitzak <spitzak at gmail.com> wrote:
>
>
> On Tue, Dec 22, 2015 at 2:32 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 don't range-check, so there is no need for this
>> > one to either. It is only called with x==0.
>>
>> Actually, I tried to stop at this function in gdb and didn't manage to
>> do it (using the scale demo). I then looked at the code and it seems
>> to me that the only way to reach this function is when both
>> reconstruction and sample kernels are IMPLUSE. That's because:
>>
>> 1. If both reconstruction and sample are *not* IMPLUSE, then of course
>> we won't reach it.
>> 2. If only one of them is IMPLUSE, than the code will immediately
>> return the value of the function of the other kernel, which is *not*
>> IMPLUSE.
>>
>> However, when I put both of them to IMPLUSE in the scale demo, the
>> picture simply disappears *and* the impluse_kernel is still not
>> reached. Actually, in that case, the integral() func is never reached
>> as well.
>>
>> What am I missing ?
>
>
> I believe at this point the calling code calculated a width of zero for the
> filter, and this caused all kinds of problems.
>
> I think you are correct that in most or all versions of this code, that
> impulse function is never called, and it could be a null pointer instead.

Well, I wouldn't go that far, but what I'm implying is maybe we can
defer this patch until a time when pixman's code will actually call
this function. Then, we can re-evaluate the patch based on the inputs
we will see.

       Oded

>>
>>
>>        Oded
>>
>> > ---
>> >  pixman/pixman-filter.c | 2 +-
>> >  1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/pixman/pixman-filter.c b/pixman/pixman-filter.c
>> > index fbc657d..00126cd 100644
>> > --- a/pixman/pixman-filter.c
>> > +++ b/pixman/pixman-filter.c
>> > @@ -45,7 +45,7 @@ typedef struct
>> >  static double
>> >  impulse_kernel (double x)
>> >  {
>> > -    return (x == 0.0)? 1.0 : 0.0;
>> > +    return 1;
>> >  }
>> >
>> >  static double
>> > --
>> > 1.9.1
>> >
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>
>